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Cathers, Ian Electrical Engineering & Telecommunications Faculty of Engineering UNSW. "Stretch signal and muscle state dependence of the tonic stretch reflex." Awarded by:University of New South Wales. School of Electrical Engineering and Telecommunications, 2000. http://handle.unsw.edu.au/1959.4/17807.
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When active skeletal muscle is stretched, it generally responds with a contraction which resists the stretch. This response is termed the muscle stretch reflex. The size (gain) and timing (phase) of the response has been found to depend on many factors including the characteristics of the applied stretch, the muscle contraction level and the subject's intention. Investigations of this stretch reflex have often involved stretches to muscle which contained frequencies either beyond the range of voluntary movement or else which could be consciously tracked. This study sought to characterise the frequency response of the stretch reflex, in terms of its gain and phase, under a variety of conditions while using stretches to the muscle which were relevant to voluntary movement, yet which were too irregular to be tracked. The types of stretch which satisfied these criteria had first to be determined by an investigation of tracking performance under different conditions of peripheral feedback. Having established the types of stretch which could be used to guarantee reflex rather than voluntary responses, the stretch reflex was investigated using stretches of different amplitude and bandwidth and spanning the full range of contraction level. Research was also undertaken to determine whether the gain and phase of the reflex response could be decoupled from the background contraction level of the muscle and to examine any associated effects on the mechanical properties of the limb. Explanatory models for some of these reflex responses were developed. An interaction between normal physiological tremor and the stretch reflex response was also investigated.
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Cernokus, Evan A. "THE EFFECT OF STRETCH WRAP PRE-STRETCH ON UNITIZED LOAD CONTAINMENT." DigitalCommons@CalPoly, 2012. https://digitalcommons.calpoly.edu/theses/857.
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There are three main factors affecting the stability of a palletized load that is unitized by a stretch wrapping mechanism. These factors include the type of unitized load, wrapping configuration and shipping method. The wrapping configuration is determined on the basis of the type of unitized load and shipping method. For this study, the aforementioned components were referred to as the package, the product, and the distribution environment. These components come together to make up a stretch wrapping system. The package corresponds to the stretch wrap film that is packaging the unitized load and pallet. The product corresponds to the goods placed on the pallet to be packaged by the stretch wrapper. The distribution environment corresponds to the hazards that the packaged product will encounter in transit. This study was designed to observe and understand the interactions between each of the components of the stretch wrap system. Prior to stretch wrapping a pallet of product, the film is elongated or pre-stretched. The elastic nature of the stretch wrap forces the film to conform around the palletized load. It is hypothesized that the film force that the stretch wrap applies to the palletized load contributes to improved load containment. Hence, the objective of this study was to determine the existence of a correlation between percentage pre-stretch to change in film force and load containment. For the study, a range of pre-stretched unitized loads were subjected to ISTA 3E distribution testing. Simultaneously the film force was monitored during the period of distribution testing. Subsequent to distribution testing, the load dispersion was quantified. The data obtained from this test suggested that there is no correlation between percentage pre-stretch and change in film force or load containment. The study also compared three methods of calculating pre-stretch: the marking wheel procedure, tapeless measure, and film cut and weigh. It was found that the most consistent method was the marking wheel procedure, followed by the cut and weigh procedure, and the tapeless measure procedure.
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Poliakov, Andrew Victor. "Stretch reflexes in human masseter /." Title page, table of contents and abstract only, 1994. http://web4.library.adelaide.edu.au/theses/09PH/09php766.pdf.
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McKnight, Rebecca Linda. "Low-stretch trees for network visualization." Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/54490.
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Low-stretch trees are spanning trees which provide approximate distance preservation for edges in the original graph by minimizing stretch. We explore the application of these trees to network visualization. In particular, we present a novel edge bundling technique, LSTB, that computes edge bundles explicitly and efficiently and does not rely on fixed vertex positions. This approach is in contrast to previous methods, which require the user to provide a layout of the input graph. We introduce an abstract framework for edge bundling methods, which provides a unifying formalization of bundling terminology and techniques, as well as a classification of such methods. Based on this framework, LSTB provides algorithmic support for sophisticated visual encodings, including dynamic layout adjustment and interactive bundle querying.
In addition, we explore the use of the multiplicative weights update method to compute a distribution over low-stretch trees in order to achieve low stretch for all edges in expectation, rather than on average. We present the results of using this distribution in place of a single low-stretch tree as a routing graph for LSTB. While the distribution provides better stretch guarantees, we find that from a visual perspective a single low-stretch tree provides a better routing graph for the LSTB edge bundling application.<br>Science, Faculty of<br>Computer Science, Department of<br>Graduate
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Apostolopoulos, Nikos. "Stretch intensity and the inflammatory response." Thesis, University of Wolverhampton, 2015. http://hdl.handle.net/2436/619238.
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Background: Stretching may be viewed as an external/internal force influencing the range of motion of the connective tissue (muscles, tendons and the myotendon unit (MTU)) The magnitude and rate of stretching may potentially induce mechanical responses of the musculoskeletal system, such as increased range of motion (ROM). The degree of the intensity of stretch (low, medium, or high) may be used to optimize recovery from muscle damage via ameliorating inflammation; this is however, a plausible hypothesis that needs to be appropriately investigated. Aims: The present project aimed to investigate: 1) whether intense stretching (IS) causes an acute inflammatory response (study 1), 2) the effects of stretching intensity (low, medium, or high) in the onset of inflammation (study 2), and 3) investigate whether stretching intensity is responsible for aiding in the recovery of the muscle, post muscle damage (study 3). Methods: Studies one and two were randomized crossover trials consisting of 12 and 11 recreational male athletes, respectively. The former investigated whether high intensity stretching can cause an acute inflammatory response, with study two examining the effects of different stretching intensities (30%, 60% and 90%) based on a participant’s perceived maximum range of motion (mROM). Blood for both studies was collected at pre-, post, and 24h post intervention, and analyzed for high sensitivity C-reactive protein (hsCRP) (study 1 and 2), and for interleukin (IL)-1β, IL-6, and tumour necrosis factor (TNF)-α (study 1). In study three, a randomized controlled trial investigated whether stretching intensity (low or high), can influence the recovery from muscle damage. Thirty participants were randomized into three groups, a) low intensity stretching (LiS) (30-40% ROM), b) high intensity stretching (HiS) (70-80% ROM) and c) Control group. All participants performed both eccentric (EPT) and isometric peak torque (IPT) tests prior to a muscle damage protocol (MDP) (baseline). Participants were then assessed for EPT and IPT for three consecutive days post MDP. Soreness levels were recorded immediately post muscle damage and at 24, 48, and 72h, with blood samples collected at pre, 24, 48, and 72h post muscle damage and analyzed for Creatine Kinase (CK) and hsCRP. Results: Study one revealed a significant increase in hsCRP (P = 0.006) when comparing IS to Control condition, also confirmed by the effect size analyses. In study two, low (30% of mROM), and medium (60% of mROM) intensity stretching did not elicit an inflammatory response while a pronounced inflammatory response was observed when comparing 30 to 90 and 60 to 90% mROM. In study three, LiS showed a significant increase in EPT compared to both HiS and Control, and these findings were confirmed by magnitude based inferences analyses (i.e. LiS was associated with a positive effect for both IPT and soreness levels compared to Control and HiS). Blood biomarkers were associated with inconsistent effects compared to Control and HiS for all three-time periods. Conclusions: This thesis provides preliminary results suggesting that increased stretching intensity may be responsible for causing an acute inflammatory response. In addition, it was observed that LiS might be associated with faster recovery from muscle damage with respect to muscle function (EPT and IPT) and soreness levels. More research is needed to investigate these findings further.
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Mohamed, Raja Roslan Raja. "Structure-property relationships in biaxially stretched amorphous PET applicable to thermoforming and stretch blow moulding." Thesis, Queen's University Belfast, 2017. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.728400.
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In thermoforming and Injection stretch blow moulding, amorphous Polyethylene terephthalate (aPET) is stretched to form products. While stretching, the microstructures change and have influence on final product properties. Therefore, the main aim of this work was to provide a fundamental understanding of microstructures evolvement during biaxial stretching of aPET in conditions applicable to thermoforming and injection stretch blow moulding as well as their effect on thermal and mechanical properties. Specimens were cut out from a commercial grade extruded aPET sheets which has a similar intrinsic viscosity to injection stretch blow moulding (ISBM) aPET and stretched using Queen's Biaxial Stretching machine under various sets of parameters namely temperature, strain rate, stretch ratio and mode of stretching, whilst mimicking the industrial processing conditions. The stress-strain behaviour during stretching was then analysed. The stretched specimens were then characterised employing a Fourier Transform Infrared with Attenuated Total Reflectance (FTIR-ATR) for gauche and trans conformers, a Differential Scanning Calorimeter for heat-crystallisable content, crystallinity and thermal properties, FTIR-ATR with polariser for orientation parameters, and a tensometer for mechanical properties. Statistical tools were also employed to determine the significance of changes and correlate the structural changes as well as the thermal and mechanical properties. The onset of strain hardening that impedes viscous flow during stretching can be attributed to the intermolecular attractions between the aligning and orientating chain. This is a new perspective on what may cause strain hardening. The structural changes may have good linear correlation between each other, depending on the stretching parameters employed. The heat-crystallisable region was found to be the determining factor in strain induced crystallisation as well as the stretching parameters. The relationship between the properties, thermal and mechanical, is determined by complex interactions between the measured structural characteristics.
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Nikitina, Tatiana. "An asymmetric bilateral model of stretch reflexes." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0002/MQ44031.pdf.
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Nikitina, Tatiana. "An asymmetric bilateral model of stretch reflexes /." Thesis, McGill University, 1997. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=20512.
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A bilateral stretch reflex model was built based on asymmetric agonist---antagonist reflex connections at the ankle. The overall dynamics were analyzed using Mason's rule algebra. The model predicts the characteristic agonist and antagonist responses to stretch. Simulations with pulse displacements and random perturbations are in qualitative agreement with experimental data and suggest a mechanism whereby the mean absolute velocity of the perturbations could depress the stretch reflex at the spinal level. This implies that spinal neural circuits can calculate and carry out their own integrative functions and, in particular, modulate the stretch reflex gain.
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Boltyanskiy, Rostislav. "Mechanical Response of Single Cells to Stretch." Thesis, Yale University, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10160860.
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<p> A living cell is a complex soft matter system far from equilibrium. While its components have definite mechanical properties such as stiffness and viscosity, cells consume energy to generate force and exhibit adaptation by modulating their mechanical properties through regulatory pathways. In this dissertation, we explore cell mechanics by stretching single fibroblast cells and simultaneously measuring their traction stresses. Upon stretch, there is a sudden, drastic increase in traction stresses, often followed by a relaxation over a time scale of about 1 minute. Upon release of stretch, traction stresses initially drop and often recover on a similar time scale of about 1 minute. We show that a minimal active linear viscoelastic model captures essential features of cell response to stretch. This model is most successful in describing the response of cells within the first 30 seconds of stretch. While perturbations of myosin and vinculin change quiescent traction stresses, they surprisingly have no significant impact on the stiffness or viscoelastic timescale of the cells. On longer time scales, cells may show an adaptive response to stretch that contradicts the minimal mechanical model. The probability of an adaptive response is significantly reduced by myosin de-activation and vinculin knockout. Therefore, we find that while vinculin and myosin are not important in determining passive mechanical properties of cells, such as stiffness and viscosity, they play a significant role in the adaptive mechanisms of cell response to stretch. To perform this work, we have built a novel micro stretching device compatible with live cell microscopy and developed a computational tool to analyze data from large traction stresses. Therefore, this dissertation's contribution is two-fold: (1) a novel experimental approach to explore the mechanics of living cells, and (2) a new model and framework for understanding the mechanical response of cells to stretch.</p>
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Thomas, Rebecca Ann. "Effect of stretch on the bronchial epithelium." Thesis, University of Leicester, 2004. http://hdl.handle.net/2381/29487.
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This thesis describes the use of a model of cell deformation to measure the effect of stretch on mediator release or expression by airway epithelial cells, and to assess the method of mechanotransduction in these cells. Cells were cyclically stretched using the Flexercell system delivering biaxial stretch. IL-8 release by BEAS 2B cells was increased by cytokine stimulation and stretch, in a dose, time and rate dependent manner, whereas RANTES levels in the cell supernatant and cell surface ICAM-1 expression decreased after stretch. 30% elongation at 20 cycles/minute for 24 hours increased IL-8 levels by over 100% (p<0.01). Changes in IL-8 and RANTES RNA correlated with the effect on protein levels. Stretch did not adversely effect cell viability. The novel use of primary bronchial epithelial cells in stretch experiments is reported, with, in contrast to the BEAS 2B cell line, no effect of stretch on IL-8 release by these cells.;To interpret how the cells were sensing the stretch stimulus, signalling via integrins was blocked using an inhibitor of Rho (R&barbelow;as Homologous) associated kinases, which inhibited the effect of stretch on IL-8 release by the BEAS 2B cells, but not the effect on RANTES release or ICAM-1 expression. Blocking individual integrins did not affect the stretch response. Paxillin was visualised by indirect immunofluorescence to study the effect of stretch on the distribution of focal contacts and the organisation of the actin cytoskeleton. This demonstrated that stretch caused dramatic disassembly of focal adhesions and resulted in the redistribution of paxillin to the peri-nuclear region.
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Carter, Nicholas James. "Stretch activation in insect fibrillar flight muscle." Thesis, University of York, 1995. http://etheses.whiterose.ac.uk/14010/.
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Vedula, Siddharth. "Ankle stretch reflexes during anticipatory postural adjustments." Thesis, McGill University, 2009. http://digitool.Library.McGill.CA:8881/R/?func=dbin-jump-full&object_id=32517.
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Miller, John Edward. "Bend-stretch forming of rectangular aluminum extrusions /." Full text (PDF) from UMI/Dissertation Abstracts International, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3008394.
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Trajano, Gabriel Siqueira. "Neuromuscular factors affecting stretch-induced torque loss." Thesis, Edith Cowan University, Research Online, Perth, Western Australia, 2014. https://ro.ecu.edu.au/theses/1284.
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The mechanisms underpinning the immediate torque loss induced by acute, static muscle stretching are still not clear. The current research was designed to examine the neuromuscular factors influencing this torque loss. In Study 1, the contributions of central versus peripheral factors to the stretch-induced torque loss were investigated. Measures of central drive, including the EMG amplitude normalised to the muscle compound action potential amplitude (EMG:M), percent voluntary activation (%VA) and first volitional wave amplitude (V:M), and measures of peripheral function, including the twitch peak torque and 20:80 Hz tetanic torque ratio were made before, and immediately and 15 min after a 5-min continuous plantar flexor stretch. There was a 15.7% (p
Alternatively, intermittent (i.e. repeated) stretching commonly performed by athlete and clinical populations causes cycles of ischaemia-reperfusion, increasing the likelihood of contractile failure. Therefore, Study 2 was designed to determine whether intermittent stretch might cause greater torque loss when compared to continuous stretch, and to quantify the potentially greater peripheral effect. The main findings were that intermittent stretch induced a greater torque loss (-23.8%; p
Central drive failure can clearly be of spinal origin, and it is reasonable to speculate that muscle stretch might affect the afferent-mediated motor neurone facilitatory system. Thus, in Study 3 a vibration-stimulation protocol (vib+stim) was used to elicit reflexmediated muscular contractions during two experiments. In Experiment 1, vib+stim was imposed with the ankle joint plantar flexed (+10°), neutral (0°) and dorsiflexed (-10°). Torque and EMG amplitudes during vibration and during the self-sustained torque period after vib+stim were greater in dorsiflexion, providing method validation. In Experiment 2, vib+stim was imposed twice before (Control) and immediately, 5, 10 and 15 min after a 5-min intermittent stretch protocol. Torque and EMG amplitude were depressed immediately after stretching during both vibration (-60% and –41%, respectively; p
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Soutoudeh, Mohammad. "Use of a newly designed equi-biaxial stretch device to study stretch-induced apoptosis of vascular smooth muscle cells /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1998. http://wwwlib.umi.com/cr/ucsd/fullcit?p9913164.
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Law, Roberta. "Effects of a three-week hamstrings stretch program on muscle extensibility and stretch tolerance in patients with chronic musculoskeletal pain." Connect to full text, 2009. http://hdl.handle.net/2123/5420.
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Thesis (M. Phil.)--University of Sydney, 2009.<br>Title from title screen (viewed September 25, 2009) Submitted in fulfilment of the requirements for the degree of Master of Philosophy to the Faculty of Medicine. Includes bibliographical references. Also available in print form.
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Law, Roberta Yu Wai. "Effects of a three-week hamstrings stretch program on muscle extensibility and stretch tolerance in patients with chronic musculoskeletal pain." Thesis, The University of Sydney, 2009. http://hdl.handle.net/2123/5420.
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Background: Physical deconditioning is often associated with chronic pain and is believed to be a result of gradual movement inhibition and reduction of physical activities. It is common for chronic pain sufferers to present with limited muscle extensibility and poor tolerance to physical movement. Exercises are therefore prescribed to assist in regaining muscle extensibility, strength, fitness and endurance. Of particular interest is stretch, a type of exercise aimed at increasing muscle extensibility. Stretch is commonly prescribed as part of physical rehabilitation in pain management programs, yet little is known of its effectiveness in the chronic pain population. Aim: The aim of this randomised controlled trial was to investigate the effects of a three-week stretch program on muscle extensibility and stretch tolerance in patients with chronic musculoskeletal pain. Methods: Thirty adults with pain persisting for at least three months and limited hamstring muscle extensibility were recruited from patients enrolled in a multidisciplinary pain management program at a Sydney Hospital. A within-subject design was used, with one leg of each participant randomly allocated to an experimental (stretch) condition and the other to a control (no stretch) condition. The hamstring muscles of the experimental leg were stretched for one minute a day over a three-week period, whilst the hamstring muscles of the control leg were not stretched during this time. This intervention was embedded within a pain management program and supervised by physiotherapists. Primary outcome measures were muscle extensibility and stretch tolerance, reflected by passive hip flexion angles produced with standardised and non-standardised torques, respectively. Initial measures were taken prior to the first stretch on day one and final measures were taken one to two days after the last stretch. A blinded assessor was used for all testing. Results: After three weeks of intervention, stretch did not increase muscle extensibility (mean between-group difference in hip flexion was 1 degree; 95% CI -2 to 4 degrees) but did improve stretch tolerance (mean between-group difference in hip flexion was 8 degrees; 95% CI 5 to 10 degrees). Conclusion: Three weeks of stretch increases tolerance to the discomfort associated with stretch but does not change muscle extensibility in patients with chronic musculoskeletal pain. This study provides support for the ongoing incorporation of stretch in pain management programs, where stretch may be conceptualised as a graded exposure to movement and assisting in the restoration of normal activity and function.
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Law, Roberta Yu Wai. "Effects of a three-week hamstrings stretch program on muscle extensibility and stretch tolerance in patients with chronic musculoskeletal pain." University of Sydney, 2009. http://hdl.handle.net/2123/5420.
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Master of Philosophy (MPhil)<br>Background: Physical deconditioning is often associated with chronic pain and is believed to be a result of gradual movement inhibition and reduction of physical activities. It is common for chronic pain sufferers to present with limited muscle extensibility and poor tolerance to physical movement. Exercises are therefore prescribed to assist in regaining muscle extensibility, strength, fitness and endurance. Of particular interest is stretch, a type of exercise aimed at increasing muscle extensibility. Stretch is commonly prescribed as part of physical rehabilitation in pain management programs, yet little is known of its effectiveness in the chronic pain population. Aim: The aim of this randomised controlled trial was to investigate the effects of a three-week stretch program on muscle extensibility and stretch tolerance in patients with chronic musculoskeletal pain. Methods: Thirty adults with pain persisting for at least three months and limited hamstring muscle extensibility were recruited from patients enrolled in a multidisciplinary pain management program at a Sydney Hospital. A within-subject design was used, with one leg of each participant randomly allocated to an experimental (stretch) condition and the other to a control (no stretch) condition. The hamstring muscles of the experimental leg were stretched for one minute a day over a three-week period, whilst the hamstring muscles of the control leg were not stretched during this time. This intervention was embedded within a pain management program and supervised by physiotherapists. Primary outcome measures were muscle extensibility and stretch tolerance, reflected by passive hip flexion angles produced with standardised and non-standardised torques, respectively. Initial measures were taken prior to the first stretch on day one and final measures were taken one to two days after the last stretch. A blinded assessor was used for all testing. Results: After three weeks of intervention, stretch did not increase muscle extensibility (mean between-group difference in hip flexion was 1 degree; 95% CI -2 to 4 degrees) but did improve stretch tolerance (mean between-group difference in hip flexion was 8 degrees; 95% CI 5 to 10 degrees). Conclusion: Three weeks of stretch increases tolerance to the discomfort associated with stretch but does not change muscle extensibility in patients with chronic musculoskeletal pain. This study provides support for the ongoing incorporation of stretch in pain management programs, where stretch may be conceptualised as a graded exposure to movement and assisting in the restoration of normal activity and function.
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Balachandran, Kartik. "Aortic valve mechanobiology - the effect of cyclic stretch." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/39486.
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Aortic valve disease is among the third most common cardiovascular disease worldwide, and is also a strong predictor for other cardiac related deaths. Altered mechanical forces are believed to cause changes in aortic valve biosynthetic activity, eventually leading to valve disease, however little is known about the cellular and molecular events involved in these processes. To gain a fundamental understanding into aortic valve disease mechanobiology, an ex vivo experimental model was used to study the effects of normal and elevated cyclic stretch on aortic valve remodeling and degenerative disease. The hypothesis of this proposal was that elevated cyclic stretch will result in increased expression of markers related to degenerative valve disease. Three aspects of aortic valve disease were studied: (i) Altered extracellular matrix remodeling; (ii) Aortic Valve Calcification; and (iii) Serotonin-induced valvulopathy. Results showed that elevated stretch resulted in increased matrix remodeling and calcification via a bone morphogenic protein-dependent pathway. In addition, elevated stretch and serotonin resulted in increased collagen biosynthesis and tissue stiffness via a serotonin-2A receptor-mediated pathway. This work adds to current knowledge on aortic valve disease mechanisms, and could pave the way for the development of novel treatments for valve disease and for the design of tissue engineered valve constructs.
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Pasquero, Jérôme. "Stress : a tactile display using lateral skin stretch." Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=80132.
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This thesis describes a new tactile display device (Stimulator of Tactile Receptors by Skin Stretch or STReSS) exploiting lateral skin stretch of the fingertip to create tactile sensations. The device consists of an array of one hundred piezoelectric bending actuators applying local strain patterns on the user's fingertip. It was found that manufacturing the piezoelectric material in a comb shape facilitates the device's fabrication process, allows for a spatial resolution of one actuator per mm2, and guarantees high structural strength for the display. Simple but creative electronics drive the system at a 700 Hz refresh rate and keep the device compact and portable. The tactile display's manufacturing process and the controlling electronics are described. Finally, some tactile sensations experienced with the display are reported informally.
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Cooper, Patricia J. "Stretch effects on cardiac electrophysiology : chronotropy and arrhythmogenesis." Thesis, University of Oxford, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.442383.
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Edin, Benoni B. "Classification of muscle stretch receptor afferents in humans." Doctoral thesis, Umeå universitet, Fysiologi, 1988. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-101350.
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The response patterns of human stretch receptors in the finger extensor muscles of the forearm were studied using the microneurography technique. Single-unit recordings were obtained from one-hundred and twenty-four afferents. A procedure was developed to classify the units in muscle spindle primary afferents, secondary afferents, and Golgi tendong organ afferents. The procedure allows an objective and reproducible classification on the basis of the afferents’ responses to a series of tests which individually are non-conclusive. It was demonstrated that maximal twitch contractions can be elicited in the finger extensor muscles of the forearm, without causing undue discomfort to the subjects, or hazarding the single-unit recording. The response of the units to this test allowed, in most cases but not always, a separation in muscle spindle and tendon organ afferents. Thus the test was not adequate for an unequivocal classification. Three discrete response parameters were extracted from ramp-and-hold stretches, viz. the presence or absence of an initial burst and a deceleration response, and prompt silencing at slow muscle shortening. The distributions of the parameters were significantly different among the three unit types. These parameters which were pair-wise independent constituted a set of considerable discriminative power. It was shown that human muscle spindles have about the same static position sensitivity to fractional muscle stretch as previously found in animals. Stretch sensitization was demonstrated by rapid, repeated stretches of the muscle which enhanced the réponse to subsequent slow stretches of muscle spindles. Sensitization was different with primary and secondary muscle spindle afferents whereas Golgi tendon organ afferents never displayed stretch sensitization. One-to-one driving with small-amplitude sinusoidal stretches superimposed on ramp-and- hold stretches was almost exclusively seen with primary muscle spindle afferents, whereas secondaries seldom and tendon organ afferents never displayed driving. The afferent responses during slowly increasing isometric contractions and rapid relaxations were analysed. An increased discharge rate on relaxation was common among spindle afferents whereas it was never seen in tendon organs afferents. Two separate groups of spindles afferents were found with regard to fusimotor recruitment. The largest group was recruited at rather low and variable contractile forces whereas the smaller group was not recruited at all. The proportions of the three unit types, spindle primary, spindle secondary, and Golgi tendon organ afferents were estimated from a preliminary classification and the distribution of the eight response features were analyzed for each class of afferents. On the basis of these estimates and the response pattern of the individual unit Bayes’ theorem was used to calculate the probabilities that the unit was a spindle primary, a spindle secondary, or a tendon organ afferent. Estimates indicate that about 19 out of 20 muscle afferents are correctly classified when all eight features are analyzed.<br><p>Diss. (sammanfattning) Umeå : Umeå universitet, 1988, härtill 6 uppsatser.</p><br>digitalisering@umu
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De, Nicola Gian Felice. "Stretch activation in muscle : a Ca²+ independent mechanism?" Thesis, Open University, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.446294.
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Parris, Andrew Nicholas. "Precision stretch forming of metal for precision assembly." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/10916.
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Quiroga, Álvarez Xarxa. "Plasma membrane mechanosensing upon stretch-induced topography remodelling." Doctoral thesis, Universitat de Barcelona, 2021. http://hdl.handle.net/10803/672367.
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Five years ago, I started walking this path that now seems like an entire life. Although everyone around tried to explain how this would feel, none of their explanations could have match what it has been in the end. And this is exactly how living systems are, at all levels. The harder the scientists try to feed our curiosity taking closer looks to them, inspecting the question from a different angle, and despite all the previous knowledge that we could gather; the more they surprise us and reveal new ways of sensing, reacting and adapting to the environment. And I think this is exactly what drove me here. I wanted to understand how this is done. I wanted to “see” it. How is it possible that a cell “understands” what is going on around? Which are the parameters that they sense? Biochemistry alone does not answer the question.
In a crowded environment, such as it is our body, cells are exposed to thousands of mechanical stimuli too. And those can be also harnessed and transformed into chemical responses as a way of signalling. While the classical biochemical inputs have long been studied, loads of questions remain open about how cells interpret those physical stimuli around them, and microscopy comes as a powerful technique to try to answer these queries.
In that sense, this thesis represents a small approach in trying to unravel how the plasma membrane, the first boundary between the cell and the extracellular media, can receive mechanical stimuli and convert them into biochemical signals amenable for the cell. To try to answer this question, this work starts with an introduction to the structure and physicochemical characteristics of the plasma membrane. An overview of the cortical component of the cytoskeleton, intrinsically interconnected to this structure, is also provided. Next, a summary of the literature available on how the plasma membrane can perceive mechanical
stimuli and which are the associated biochemical responses triggered by them is included as well. This part is based on a review article published by my colleague and co-supervisor Dr. Le Roux and myself at Philosophical Transactions B as part of the 2019 issue “Forces in cancer” [1].
After the introduction, chapter 2 describes the objectives of this study, which can be summarised as trying to unravel the way in which cells couple mechanical signals at their plasma membrane to biochemical cascades that mediate a response to those. Following, chapters 3 and 4 compose the main body of this thesis, including the methods and the experimental results coming from this research work. Both sections constitute a scientific article that has been recently submitted for publication. In chapter 3 the simplified model chosen to study the question of how cells sense and integrate mechanical stimuli at their plasma membrane is described. This consisted in submitting fibroblast to a controlled stretch-release cycle, forcing them to quickly adapt their shape, mimmicking a highly-relevant scenario in physiology. Chapter 4 recapitulates the way in which plasma membrane reacted to this mechanical perturbation. In the first place, the structure reacted by passively forming evaginations on the nanometric scale of homogeneous size and shape. These evaginations are next recognised by the I- BAR protein IRSp53, which subsequently organizes a node of actin polymerisation dependent on Rac1 and Arp2/3 that mediates the flattening of the structures. Absence of IRSp53 results, thus, in an impaired recovery of homeostasis after stretch. To reinforce the obtained experimental results, theoretical framework to model the mechanics of the system was generated in collaboration with the group of Dr. Arroyo at the Centre Internacional de Mètodes Numèrics en Enginyeria (CIMNE). The aim of this model was to describe how a network generated by the Arp2/3 complex, until now described to push, is able to generate in-plane forces that mediate the ironing of the evagination. Chapter 5 includes a discussion about the limitations of the technique, the novelty of the presented findings, the possible physiological scenarios where the described mechanochemical pathway can be of relevance and, finally, some exciting and unexplored questions that remained open after this work.
Additionally, other scientific production obtained during this thesis consisting in unexplored results or work belonging to other publications, has been added at the end of this manuscript in four appendixes. On the first one, I describe all the efforts made during the first 1 year and a half of the PhD to improve immunostaining technique for plasma membrane bound proteins in order to try
to stain endogenous BAR proteins. The second appendix gathers the findings obtained from the silencing assay of BAR candidates likely to recognise the curved shape of the stretch-release generated evaginations. The third appendix contains experimental results part of a different publication from Le Roux et al. now under review in Nature Communications [2]. Here, I studied the response of the N-BAR protein Amphiphysin after mechanical stimulation in cells. A fourth appendix including scanning electron microscopy representative images of stretch-release generated evaginations in other cell lines is also added. Finally, I included two more appendix containing the sequencing of all the IRSp53 plasmids used for the body of the work of this thesis and the MATLAB code used for analysis of evaginations flattening dynamics after stretch.
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Suslak, Thomas James. "There and back again : a stretch receptor's tale." Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/10474.
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Mechanotransduction is fundamental to many sensory processes, including balance, hearing and motor co-ordination. However, for such an essential feature, the mechanism(s) that underlie it are poorly understood. The mechanotransducing stretch receptors that relay information on the tonicity and length of skeletal muscles have been well-defined, particularly at the gross anatomical level, in a wide variety of species, encompassing both vertebrates and invertebrates. To date, there exists a wealth of data describing them, anatomically, as well as good electrophysiological data from stretch receptors of some larger organisms. However, comparatively few studies have succeeded in identifying putative mechanotransducing molecules in such systems. Nonetheless, this class of sensory mechanotransducers perhaps offer the best means of identifying molecules that permit the stretch-sensitivity of such endings, revealing new information about the underlying mechanisms of stretch receptors, and mechanoreceptors more generally. However, a different approach is clearly needed; a theoretical approach, utilising mathematical modelling, offers a powerful means of pooling the current wealth of knowledge on the reported electrophysiological behaviour of muscle stretch receptors. This study, therefore, develops an extended theoretical model of a stretch receptor system in order to reproduce, in silico, the reported behaviour of both vertebrate and invertebrate stretch receptors, within the same modelling environment, thus enabling the first quantitative framework for comparing these data, and moreover, making predictions of the likely roles of specific molecular entities within a stretch receptor system. Subsequently, this study utilises a model in vivo system to test these theoretical predictions. The genetic toolbox of D. melanogaster offers a wide range of tools that are extremely suitable for identifying mechanotransducing molecules in stretch receptors. However, very little is currently known about such endings in this organism. This study, therefore, firstly characterises a putative stretch receptor organ in larval Drosophila, the dbd neuron, via a novel experimental approach. It is shown that this neuron exhibits known properties of stretch receptors, as previously observed in other, similar organs. Furthermore, these observations bear out the predictions of the mathematical model. Having defined the dbd neuron as a muscle stretch receptor, pharmacological and genetic assays in this system, combined with predictions from the mathematical model, identify a key role for the recently-discovered DmPiezo protein as an amiloride-sensitive, mechanically-gated sodium channel (MNaC) in dbd neurons, with TRPA1 also acting in this system in a supporting role. These data confirm the essential role of an MNaC in mechanosensory systems, but also supply important evidence that, whilst the electrophysiological mechanisms in stretch receptors are remarkably similar across taxa, different species likely employ various molecular mechanisms to achieve this.
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Taylor, Simon Crispin. "Burning velocity and the influence of flame stretch." Thesis, University of Leeds, 1991. http://etheses.whiterose.ac.uk/2099/.
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A new technique is presented for determining burning velocities and stretch effects in laminar flames, and applied to a range of fuel/air mixtures. The speeds of expanding spherical flames, measured by high-speed schlieren cine-photography, are shown to vary with flame radius. A simple phenomenological model has been developed to analyse the data and obtain the one-dimensional flame speed by extrapolation to infinite radius. The validity of the simple model has been tested by using it to analyse the results of detailed simulations of expanding spherical flames. The true one-dimensional flame speeds in this case are known from planar flame modelling using the same kinetic scheme. The simple model predicted flame speeds within 2% of the true values for hydrogen/air mixtures over most of the stoichiometric range. This demonstrates that the extrapolation procedure is sound and will produce reliable results when applied to experimental data. Since the flame speeds derived from experiments are one-dimensional values, multiplying them by the density ratio gives one-dimensional burning velocities (s,'). Maximum burning velocities of hydrogen, methane, ethane, propane and ethylene mixtures with air were 2.85 ms-', 0.37 ms-', 0.41 ms-', 0.39 ms-' and 0.66 ms-' respectively. These are considerably smaller than most burner-derived values. The discrepancies can be explained by flow divergence and stretch effects perturbing burner measurements. The rate at which the measured flame speed approaches its limiting value depends on flame thickness and flame stretch. By subtracting the flame thickness term, the influence of flame stretch, expressed as the Markstein length, can be derived. Again values are given across the whole stoichiometric range of all fuels listed above, and form the most complete set of Markstein lengths reported to date. The Markstein lengths are negative in lean hydrogen and methane and in rich ethane and propane mixtures: this means that stretch increases the burning rate. They are positive in all other mixtures, showing that stretch decreases the burning rate. The results are in line with predictions based on Lewis number considerations. An alternative method of deriving one-dimensional burning velocities and Markstein lengths has been investigated. Burning velocities were measured at different stretch rates in flames in stagnation-point flow. Particle tracking was used to derive burning velocities referred to the hot side of the flame from the upstream values. The two burning velocities extrapolated to different one-dimensional values, both of which differed slightly from the expanding flame results. The suggested reason is that the upstream velocity gradient is not an accurate measure of the stretch experienced by the flame. Markstein lengths were consistent with those from the expanding flame method but the uncertainties were much larger. The method in its present form is therefore useful qualitatively but not quantitatively.
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Guo, Hong. "Effects of biaxial stretch on arteriolar function in vitro." Thesis, [College Station, Tex. : Texas A&M University, 2006. http://hdl.handle.net/1969.1/ETD-TAMU-1739.
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Small, Daniel Leroy. "Biophysical and pharmacological characterization of stretch-activated K(+) channels." Thesis, University of Ottawa (Canada), 1995. http://hdl.handle.net/10393/9869.
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Mechanosensitive ion channels were studied in various preparations (Lymnaea stagnalis cultured neurons, and ventricular heart cells, Aplysia californica mechanosensitive neurons, and Xenopus oocytes) using cell-attached and excised inside-out patch-clamp techniques to characterize their biophysical and pharmacological properties. It has been demonstrated that a well studied K-selective channel which plays an important role in "cellular learning" in Aplysia mechanosensory neurons, is stretch-activated. Using multi-channel patch analysis I have provided further evidence that this channel is indeed a stretch-activated (SA) K$\sp+$ channel similar to those found in virtually all molluscan neurons. I demonstrated that the number of SAK$\sp+$ channels in a patch is finite and the response saturable. Kinetic stationarity was tested. In patches which passed the stationarity tests and in which channels were found to be independent and identical, the kinetics were determined. The kinetic analysis yielded results consistent with the hypothesis that S-channels (those which responded to FMRF-amide and to 5-HT) were identical to SA K$\sp+$ channels (those which were stretch-activatable). I then tested the hypothesis that all molluscan SA K$\sp+$ channels were S-like in that they were modulated by neurotransmitters via second messengers. I found that the inherent variability of normal channel activity prohibited adequate testing of this hypothesis even when a homogeneous population of cells containing similar SA K$\sp+$ channels was examined. Dynamics. When care was taken to obtain gigaseals in a gentle fashion (10 mmHG suction) and disruption to the patch integrity was minimized, SA K$\sp+$ channels in Lymnaca neurons exhibited dynamic characteristics. These characteristics included a delayed response to rapid suction steps. The delay lessened with suction steps of increasing magnitude. The delay phenomenon was fragile in nature in that the delay was lost with repeated suction stimuli of the same magnitude of by non-gentle seal formation. The delay was voltage independent. Cells left in culture longer (4, 5, and 6 days as opposed to 1 and 2 days), responded to similar stimuli with longer delays. I found SA K$\sp+$ channels to be blocked by extracellular TEA (IC$\sb{50} = {\sim}50$mM), but not by intracellular TEA, extracellular diltiazem or Gd$\sp{3+}$. Extracellular amiloride and quinidine blocked SA K$\sp+$ channels with IC$\sb{50}$s of $\sim$2.15 mM and $\sim$0.75 mM respectively. Ethanol (3%) had no apparent effect on SA K$\sp+$ channels yet reduced the efficacy of quinidine block. Permeation. Given that Lymnaea SA K$\sp+$ channels seem to be K-selective channels which are specialized to avoid sensing membrane tension under normal conditions, I characterized the pore properties with the intent to make comparisons to other SA channels and K$\sp+$ channels whose structure/function relations are fairly well understood. I found that the pore of SA K$\sp+$ channels has an affinity for inward and outward moving K$\sp+$ currents of 28.1 $\pm$ 5.0 mM and 91.9 $\pm$ 6.7 mM. SA K$\sp+$ channels exhibited an anomalous mole fraction effect with mixtures of Rb$\sp+$ indicative of a multi-ion pore. (Abstract shortened by UMI.)
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Bock, Przemek John. "Modulation of stretch reflex excitability in quiet human standing." Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=82471.
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Stretch reflex excitability was measured during quiet standing by using a bilateral electro-hydraulic actuator to apply perturbations of angular position to the ankle. Subjects were instructed to stand quietly while pulse displacements were applied at random times. Position, torque, gastrocnemius-soleus EMG, tibialis anterior EMG, heel position, tibia angle, femur angle, and sacrum angle were measured. Background torque and reflex excitability varied substantially from trial to trial---reflex torque decreased as the background torque level increased; while reflex EMG increased when background torque increased. This behavior is consistent with previous findings in prone subjects. Reflex torque for a given activation level was found to vary with the initial torque derivative---reflex excitation was greater for negative torque derivatives than their positive counterparts. These findings suggest that reflex excitability in quiet human standing is modulated to optimize balance.
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Shin, Hyunshik. "Algebraic degrees of stretch factors in mapping class groups." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51910.
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Given a closed surface Sg of genus g, a mapping class f in \MCG(Sg) is said to be pseudo-Anosov if it preserves a pair of transverse measured foliations such that one is expanding and the other one is contracting by a number \lambda(f). The number \lambda(f) is called a stretch factor (or dilatation) of f. Thurston showed that a stretch factor is an algebraic integer with degree bounded above by 6g-6. However, little is known about which degrees occur.
Using train tracks on surfaces, we explicitly construct pseudo-Anosov maps on Sg with orientable foliations whose stretch factor \lambda has algebraic degree 2g. Moreover, the stretch factor \lambda is a special algebraic number, called Salem number. Using this result, we show that there is a pseudo-Anosov map whose stretch factor has algebraic degree d, for each positive even integer d such that d≤g. Our examples also give a new approach to a conjecture of Penner.
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Watkins, Penelope A. "Design for movement : block pattern design for stretch performancewear." Thesis, De Montfort University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.685304.
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Berg, Krystina Michelle. "Stretch-Dependant Tonic Force Maintenance in Rabbit Epigastric Artery." VCU Scholars Compass, 2006. http://scholarscompass.vcu.edu/etd/1435.
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The contractile state of vascular smooth muscle (VSM) plays a key role in blood pressure regulation. Abnormal VSM contractility characterizes hypertension and understanding the regulatory mechanisms of VSM may provide some insights to specific treatment of hypertension. Upon muscle stimulation, Ca2+, myosin light chain (MLC) phosphorylation, crossbridge cycling rates and force increase to high levels, but with time, force is maintained while all other parameters of muscle activation fall to low levels. Thus, contraction is divided temporally into early (phasic) and late (tonic) phases, as determined by the underlying regulatory mechanism. Muscles with more phasic characteristics have a higher peak phase while tonic muscles have both high peak and tonic. However, these muscles have similar contractile increases in Ca2+ despite their substantial differences in force production during the tonic phase of contraction. Myosin light chain phosphatase (MLCP) inhibition by RhoA Kinase (ROK) has been shown to contribute to this increased force production without simultaneous increases in calcium in a process known as Ca2+ sensitization.Epigastric artery (EA) has a unique regulatory mechanism controlled by the degree of stretch applied on the artery which produces an increase in tonic force maintenance. Tonic force in EA is blocked equally at all lengths by the ROK inhibitor Y-27632, suggesting ROK is the main mechanism of signal transduction activated.MLC-p is increased during basal compared to unstretched conditions for epigastric but not femoral artery (FA). Pharmacological MT depolymerization due to Colchicine incubation has been shown to release RhoGEF, a RhoA activator, and resulted in increased tonic force and MLC-p which were both inhibited by a ROK inhibitor.Additionally, KC1-stimulation appeared to activate MAPK and ROK pathways, while stretch alone activated a yet undetermined pathway, possibly ILK. KC1-induced contraction in FA activated TRP sensitive calcium channels during both peak and tonic phases. However, stretch in EA does not induce additional calcium influx. Thus, these data support the conclusion that an increase in length activates ROK and other kinases resulting in tonic force maintenance in EA.
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Mansfield, Catherine. "The actomyosin ATPase response to stretch in cardiac muscle." Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/9609.
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The aim of this thesis was to examine the molecular mechanism underlying the force response to stretch in the heart. The properties of cardiac muscle were studied in rat trabeculae activated by laser-flash photolysis of NPE-caged ATP at 20°C. The rate of ATP hydrolysis was determined, on a millisecond time scale, using a fluorescently labelled phosphate binding protein to measure the rate of inorganic phosphate release. The results show that an increase in sarcomere length causes an increase in isometric force with a similar response seen upon increasing thin filament activation. ATPase rate increases with thin filament activation, however, the increase in force with sarcomere length is not accompanied by a corresponding increase in ATPase rate. At a lower activation level a more substantial increase in isometric force is seen with increasing sarcomere length, compared to at a higher activation level. The results show that at a longer sarcomere length less ATP is used per unit of force produced. Interestingly, stretch of an active muscle causes a substantial and instantaneous reduction in cross-bridge ATPase activity, even though force remains high. Conversely, active shortening resulted in an increase in the ATPase rate, above that of the isometric level. The stretch applied to the active trabeculae was greater than the reach of the cross-bridges therefore cross-bridge detachment must occur, however as force remains high this must be followed by rapid reattachment. As Pi release is low during the stretch this detachment and reattachment cannot occur via the classical view of the cross-bridge cycle where attachment is preceded by ATP hydrolysis. To explain these results a branched cross-bridge cycle is suggested whereby rapid detachment and reattachment can occur without additional Pi release and ATP hydrolysis.
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Summerour, Sonya R. "Static equibiaxial stretch mediated mechanotransduction in adult cardiac fibroblasts /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1999. http://wwwlib.umi.com/cr/ucsd/fullcit?p9952652.
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Chen, Yan. "Spike pattern analysis of slowly adapting pulmonary stretch receptors." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 135 p, 2009. http://proquest.umi.com/pqdweb?did=1818417461&sid=7&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Evans, Tom. "The effects of static stretching on vertical jump performance." Huntington, WV : [Marshall University Libraries], 2006. http://www.marshall.edu/etd/descript.asp?ref=635.
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Isaksson, My, and Joe Brereton. "Att värma upp med statisk stretch eller inte? : En systematisk litteraturstudie på hur statisk stretch vid uppvärmning påverkar utfallet i höjd vid vertikalhopp." Thesis, Uppsala universitet, Åsenlöf: Fysioterapi, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-431654.
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Abstrakt Bakgrund: En allmän uppfattning är att stretching kan påskynda musklernas förmåga till återhämtning, underlätta inlärning av rätt teknik samt minska risken för överbelastningsskador i vissa idrotter (1). Det har presenterats motstridiga resultat om hur statisk stretch påverkar senor samt på de muskulära komponenterna i muscle-tendon unit (MTU). En del studier har visat att statisk stretching (SS) minskar styvheten i MTU och/eller ökar senans slakhet (4,5), vilket i sin tur leder till sämre kraft produktion och en långsammare muskelaktivering (6). Syfte: Syftet med studien var att systematiskt granska vetenskapliga artiklar gällande effekten av hur statisk stretch kombinerat med uppvärmning påverkar höjden i ett vertikalhopp hos friska unga vuxna, mätt i centimeter med hjälp av hoppmatta. Metod: Litteratursökningen genomfördes via databasen PubMed och nio artiklar inkluderades enligt kriterierna för PICO (Population, Intervention, Control & Outcome). Artiklarna granskades sedan via granskningsmallen PEDro-scale i syfte att skatta studiekvaliteten. Därefter betygsattes evidensstyrkan via SBU:s metod GRADE. Resultat: Tre av studierna konkluderar en minskning av vertikalhöjden efter stretching medan resterande sex studier fann ingen signifikant skillnad. Den sammanlagda evidensgraden av vilken effekt statisk stretchs har på vertikalhopp bedöms som begränsad. Konklusion: Efter granskning av de nio inkluderande artiklarna går det ej att säkerställa att statisk stretching påverkar utfallet av ett vertikalhopp. Hur durationen av statisk stretch kombinerat med uppvärmning påverkar höjden i vertikalhopp är ett område där det behöver bedrivas ytterligare forskning.<br>Abstractz Background: The general perception is that stretching can accelerate the muscles ability to recover, facilitate the learning of correct technique and reduce the risk of overuse injuries in certain sports (1). Conflicting results have been presented on the effects of static stretching on the tendons as well as on the muscular components on the muscle-tendon unit (MTU). Some studies have shown that static stretching (SS) reduces the stiffness of the MTU and/or increases the tendon slackness (4,5), which in turn results in poorer force production and slower muscle activation (6). Purpose: The purpose of this study was to systematically review scientific articles regarding the effect of how static stretching combined with a warm-up effects the height in a vertical jump in healthy young adults, measured in centimeters using a jumping mat. Method: The literature search was performed on the database PubMed and nine articles were included according to the criteria for PICO (Population, Intervention, Control & Outcome). The articles were reviewed by PEDro-scale in order to assess the study quality. Thereafter the strength of evidence was assessed by SBU's method GRADE. Results: Three of the included studies conclude a reduction in vertical height after static stretching while the remaining six studies found no significant difference in jump height. The total evidence grading on the effect of static stretch on vertical jumps I assessed as a limited basis. Conclusion: After a review of the nine included articles it is not possible to come to a definitive conclusion that static stretching affects the outcome of a vertical jump. How duration of static stretching combined with warm-up affects the height in vertical jumps is an area where further research needs to be conducted.
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Le, Guen Morgan. "Effets de l'application d'un stretch cyclique sur un modèle isolé de bronche humaine : étude fonctionnelle, pharmacologique et immuno−génétique." Thesis, Versailles-St Quentin en Yvelines, 2014. http://www.theses.fr/2014VERS0060/document.
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L’arbre bronchique constitue une large interface avec le milieu extérieur ce qui en fait notamment une sentinelle immunologique. Par ailleurs, il est soumis à de multiples contraintes physiques (variation de pressions lors du cycle ventilatoire) avec le développement de pathologies lorsque la réponse à ces contraintes est inadaptée. Au cours de ce travail, nous avons essayé de caractériser la réponse bronchique des voies aériennes distales à partir d’un modèle isolé de bronche humaine soumis à l’application d’un stretch unique ou cyclique tel qu’il est généré lors de la ventilation mécanique. D’un point de vue fonctionnel, le stretch unique ou cyclique s’accompagne d’une modification significative du tonus basal de la bronche avec deux étapes : l’une précoce apparaît au cours de l’exposition même des variations de tension pariétale, l’autre est tardive et apparaît à l’arrêt de l’étirement. Concernant l’étape précoce, elle se révèle robuste car aucun pré-traitement et particulièrement l’abrasion de l’épithélium ne la supprime totalement. La caractérisation de cette réponse implique notamment la voie des NO synthases et des Rho-A kinase. La réponse tardive fait quant à elle intervenir l’épithélium ainsi que la voie des NO-synthase suggérant un rôle prépondérant du NO. Par contre, ces modifications de force au repos sont indépendantes de la sécrétion de médiateurs inflammatoires détectés par ELISA. L’approche génétique renforce par contre le rôle du tissu de soutien bronchique en activant la synthèse de collagène (MMP-9). Au total l'application d'une contrainte cyclique renforce la bronchoconstriction par inhibition de la voie des NOsynthases et de la mécanotransduction<br>The tracheo-bronchial tree is a true immunologic sentinel related to the huge interface with the external environment. Moreover, it is submitted to variable physical strains (tidal ventilation and variation in pressure) and an excessive response leads to the genesis of some pathology as hyperresponsiveness. The aim of this work on an isolated organ model was to characterize the human bronchial response to a single or repetitive and physiological stretch as observed during mechanical ventilation. From a functional perspective, a single strain or a cyclic stretch significantly increased the basal tone of the human bronchus with a two-step response: the early response appears during cycling and the delayed after the stretch has ceased. The early response is robust then no pre-treatment and especially epithelial removal totally inhibits it. This response implies NO synthase and Rho-A kinase pathway with a reduction of the developed basal tone with these inhibitors. As it concerns the late response, it involved epithelium and NO synthase suggesting a prominent action of NO. Inflammatory mediators are not directly involved in the rise of basal tone because stretch-induced secretion as detected with ELISA is very low. Genomic approach transiently activates transcription of genes for MMP-9, involved in the collagen production and consequently in the support tissue of the bronchial tree. As a conclusion, cyclic stretch enhances bronchoconstriction by inhibition of the NO-synthase pathway and mechanotransduction
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Tung, James 1975. "Task-dependent modulation of stretch reflex stiffness in the ankle." Thesis, McGill University, 2002. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=79266.
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The stretch reflex is an involuntary contraction produced in response to muscle stretch. Despite extensive research, its role in the control of movement and posture remains controversial. One reason for this is that the torque output produced by reflex activity has been studied in only a limited number of tasks and behaviours. The main thrust of this thesis is to examine whether the central nervous system (CNS) modifies stretch reflex properties to suit the task.<br>An electro-hydraulic actuator applied perturbations to the ankles of five subjects while they performed position-matching (PM) and torque-matching (TM) tasks. Stretch reflex properties were determined using a new closed-loop, reflex identification algorithm that analytically separated the torques produced by stretch reflexes from the overall ankle torque. Stretch reflex gain was greater in the PM task than for the TM task, under matched conditions.
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Calota, Andra. "Reliability of spasticity measurement based on tonic stretch reflex threshold." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=111947.
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Studies suggest that deficits in central regulation of stretch reflex thresholds (SRT) underlie both spasticity and other disorders of motor control. We investigated intra- and inter-evaluator reliability to quantify spasticity based on tonic SRT (TSRT) and the relationship between TSRT and Modified Ashworth Scale (MAS, clinical assessment of resistance to stretch). Spasticity was evaluated in 20 subjects with chronic stroke-related spasticity in two different days, by three evaluators. Twenty different velocity-dependent dynamic SRT (angle where biceps brachii EMG signal increased for a given velocity of stretch) were recorded. TSRT (excitability of motoneurons at 0°/sec) was then computed. Spasticity was also estimated with MAS. Reliability was moderately good for subjects with moderately high spasticity (intra--evaluator: 0.46 to 0.68, inter--evaluator: 0.53 to 0.68). There was no correlation between TSRT and MAS since they measure different phenomena. TSRT is a promising new measure of spasticity. Further improvements for its quantification are suggested.
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Tsai, I.-Chin. "The influence of woven stretch fabric properties on pattern design." Thesis, De Montfort University, 2001. http://hdl.handle.net/2086/10746.
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Conventional pattern construction and pattern making methods typically require the size measurements of a range of standard mannequins or human bodies in order to construct the varying pattern blocks for garment design. These various methods and skills, in the fashion industry, factory or studio are performed by pattern makers or producers, and are refined through the garment sampling and wearer trial system (an uneconomical trial and error) used on woven garments or on woven stretch garments to produce varying garment designs. This is particularly true when fabric stretch and recovery properties and values are encountered. There is a strong alliance with the heuristic knowledge. The aim of the present work is to investigate the influence of woven stretch fabric properties on pattern construction. The stretch and recovery properties of woven stretch fabrics will be taken account for pattern reduction and alteration for the development of a suitable garment pattern to fit the body shape and to meet the comfort requirement during the body movement. The relationship between the degree of alteration and reduction and the relevant fabric stretch properties is to be established. In this thesis, the stretch and recovery properties of various woven stretch fabrics have been measured. The conventional pattern is reduced and altered based on the comfort requirement for body movement, fit to body shape and the extension and recovery properties of the woven stretch fabric. Wearer trial test of the altered garment pattern of woven stretch fabrics is carried out for subjective and objective evaluation in the reference of the traditional woven garment pattern. Their comfort and garment appearances are evaluated by a panel of judges and the wearer. The size and shape stability of garments after the wearing tests are assessed. The results demonstrated that the new pattern method was significantly better for woven stretch fabric. The garment pattern for fit and comfort can be predicated and produced according to the extension and recovery properties of fabrics.
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Agarwal, Anuj. "EFFECTS OF ACUTE STRETCH ON CARDIAC ELECTRICAL PROPERTIES IN SWINE." UKnowledge, 2013. http://uknowledge.uky.edu/cbme_etds/10.
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Stretch is known to result in an electrically less stable ventricular substrate, yet the reported effects of stretch on measured electrophysiological parameters have been inconsistent and even contradictory. The goal of this study was to evaluate the effects of acute mechanical stretch on cardiac electrical features thought to be key in generation of arrhythmia, namely restitution of action potential duration (APD), electrical memory, and onset of alternans.
Microelectrodes were used to record intracellular potentials pre, during, and post-stretch from isolated right ventricular tissues from swine. In separate experiments, the effects of two levels of stretch were quantified. Pacing protocols employing explicit diastolic interval (DI) control and cycle length (CL) control were used to obtain measures of restitution of APD, memory, and alternans of APD. Stretching the tissue had varying effects on APD, restitution and memory. Stretch increased APD, restitution slopes and memory by as much as 24, 30 and 53 % in some cases, while it decreased these by up to 18, 37 and 81 % in others. During stretch, alternans of APD were observed in some cases, which occurred at slower rates of activation than before stretch. Histology of tissue samples showed localized changes in orientation of cells relative to the direction of stretch.
Our results show that among individual trials, stretch altered the measured electrophysiological properties, sometimes markedly. However, when pooled together, these changes cancelled each other and the averages showed no statistically significant difference after stretch. A potential mechanism that explains this divergent and inconsistent response to stretch is the presence of local, micron level, variation in orientation of myocytes. Upon stretch, these divergent effects likely increase dispersion of repolarization diffusely and might thus be the reason behind the consistently observed increase in arrhythmic substrate after stretch.
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Leacock, Alan Gordon. "Numerical simulation of anisotropic plasticity in stretch formed aluminium alloys." Thesis, University of Ulster, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.369949.
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Bardswell, Sonya Caroline. "The mechanism of the slow force response to myocardial stretch." Thesis, King's College London (University of London), 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.416416.
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Santos, Artur Bonezi dos. "Avaliação da estabilidade no exercício long stretch front do pilates." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2018. http://hdl.handle.net/10183/184652.
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A estabilidade do tronco é geralmente desafiada nas sessões do método Pilates. A compreensão da estabilidade/instabilidade, desafiada pela alteração de molas e dependente do nível de treinamento dos executantes, possui grande impacto no controle do tronco. Após uma revisão sistemática foi possível verificar que a principal técnica biomecânica empregada para compreender a estabilidade do tronco é a modelagem. Sendo assim, o objetivo deste estudo foi desenvolver e avaliar um modelo biomecânico para quantificar e comparar a estabilidade do tronco em dois diferentes níveis de praticantes de Pilates e em dois diferentes níveis de intensidade do exercício long stretch front do Pilates. O exercício long stretch front, criado para utilizar o powerhouse e desafiar a estabilidade do tronco, é executado no aparelho reformer na posição de prancha e consiste na extensão de ombros. O movimento foi modelado como um sistema massa-mola sendo a rigidez (K) o parâmetro de estabilidade do tronco. Como dados de entrada foram utilizadas informações cinemáticas, de câmeras infra-vermelho, cinéticas, de células de carga acopladas ao equipamento reformer, e informações antropométricas extraídas da literatura. Foram avaliados 15 praticantes avançados de Pilates e 15 iniciantes. Os indivíduos mais experientes foram mais estáveis durante o exercício do que iniciantes, F(1,28)=7,965; η2=0,22; p=0,009. A execução dos exercícios com duas molas apresentou menor rigidez do que com uma única mola, F(1,28)=67,891; η2=0,71; p<0,001. Não houve interação entre os fatores, F(1,28)=0,587; η2=0,02; p=0,450. Quando os grupos foram comparados separadamente para cada um dos níveis de dificuldade, os mais experientes (K = 272 ± 27 Nm/rad) apresentaram maior rigidez que os iniciantes (K = 171 ± 42 Nm/rad) com uma única mola, e também com o uso de duas molas, com K = 196 ± 17 Nm/rad para os executantes experientes e K = 108 ± 21 Nm/rad para os executantes iniciantes. Conclui-se que o modelo proposto, utilizando o coeficiente de rigidez, foi capaz de quantificar a estabilidade durante o exercício longh stretch front do Pilates. O modelo também identificou as diferenças entre indivíduos mais ou menos experientes, bem como quando o exercício é executado com uma ou com duas molas.<br>Trunk stability is usually challenged during Pilates method ’sessions. The stability/instability, generated by altering springs or by the practitioner’s experience level during a Pilates exercise, has great impact in trunk control. Following a systematic review, it was observed that modelling is the main biomechanical technique applied for understanding trunk stability. Hence, this study aimed to develop and evaluate a biomechanical model for quantifying and compare trunk stability in two different Pilates practitioners levels and two different intensities of the exercise during Pilates’ long stretch front exercise. The long stretch front exercise, created for using the powerhouse and challenging trunk stability, is performed in the reformer apparatus, keeping the trunk in the plunk position while shoulder extension is performed. The movement was modelled as a spring-mass system using stiffness (K) as the parameter to express trunk stability. Model input consisted of kinematics data, obtained from infrared cameras images, kinetic data, from load cells attached to the reformer equipment, and anthropometric data, obtained from literature. Fifteen experienced and 15 beginner Pilates practitioners, who performed ten repetitions of the exercise in two difficulty levels, with one and two springs, were evaluated. Experienced subjects were more stable during the exercise when compared to beginners F(1.28)=7.965; η2=0.22; p=0.009. The exercise performed using two springs presented a lower rigidity level when compared to one spring F(1.28)=67.891; η2=0.71; p<0.001. There was no interaction between the factors , F(1.28)=0.587; η2=0.02; p=0.450. When groups were compared separately for each difficulty level, experienced (K=272 ± 27 Nm.rad-1) presented higher rigidity than beginners (K=171 ± 42 Nm.rad-1) using one spring, and also using two springs with K=196 ± 17 Nm.rad-1 for experienced performers and K=108 ± 21 Nm.rad-1 for beginners. Concludes that the proposed model is capable of quantifying stability during the Pilates long stretch front exercise using rigidity coefficient. In addition model identifies differences between more or less experienced subjects, as well as when the exercise is performed using one or two springs.
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Kroening, Karolin. "Small to large molecule speciation: Metallomics approaches stretch the horizons." University of Cincinnati / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1291050537.
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Wood, David Samuel. "Leg press stretch-shortening potentiation in male long distance runners." Birmingham, Ala. : University of Alabama at Birmingham, 2009. https://www.mhsl.uab.edu/dt/2009r/wood.pdf.
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Moyes, Bryce L. "Correlation Between the USU Stretch Test and the Pizza Fork Test." DigitalCommons@USU, 2003. https://digitalcommons.usu.edu/etd/5490.
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A correlation between the USU stretch test and the pizza fork test would allow the stretch properties of Mozzarella cheese to be measured objectively. The Utah State University (USU) Stretch Test uses a modified texture-profile analyzer to pull strands of cheese from a melted reservoir, measuring the load exerted on the probe during stretching. Parameters measured by the USU stretch test include Melt Strength (FM), which is the maximum load exerted on the probe, Stretch Load (SL), which is the load exerted on the probe at any specified point following FM, and Stretch Extension (SE), which was defined as the extension of the probe at a selected load. To begin with, it was determined that the greatest repeatability and cheese performance was obtained by tempering 50 g of shredded cheese for 45 min at 65°C and using a three-pronged hook with a diameter of 25 mm as the probe. These conditions were then applied in a correlation study in which a low correlation was seen between the USU stretch test and the pizza fork test, with the greatest correlation being seen with FM (R2 = 0.22). A more extensive look at the effect of the tempering temperature used in the USU stretch test on the degree of correlation between the two tests was conducted by tempering cheeses at 65, 70, 75, 80, and 85 °C. In this experiment, the highest correlation between the two tests was seen at both 80 and 85°C. Values of R2 at 80°C for SL10-15 and SEF (Stretch Extension at FM) were 0.75 and 0.70, respectively. At 85°C, the highest degree of correlation was seen at SL10-15 (R2 = 0.72) and SE0.1 (R2 = 0.69). A multiple linear correlation study was also conducted. A high degree of correlation between the USU stretch test and the pizza fork test was seen at 80°C when two parameters were used (SEF and SL22, R2 = 0.85, Adj. R2 = 0.80) and when four parameters were used (FM, slope from 10 to 20 em, SE0.1, and SL22, R2 = 0.97, Adj. R2 = 0.93). A set of cheese was then analyzed by the USU stretch test and the pizza fork test at three different intervals of aging (21 , 40, and 60 days after manufacture). This data was combined with previously collected data to show that the USU stretch test can be used to characterize the functional properties of a cheese using the parameters of FM, SEF, as well as SE0.1.
It was concluded that the USU stretch test can provide a better characterization of a pizza cheese than can the pizza fork test. Whereas the pizza fork test is only able to record the distance that the cheese can stretch, the USU stretch test is capable of measuring a variety of parameters, which provides not only an indication of how far the cheese will stretch, but also other important functional properties related to the cheese, such as viscosity, elasticity, and the thickness of the strands being stretched.
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Bisha, James Victor. "Correlation of the Elastic Properties of Stretch Film on Unit Load Containment." Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/27992.
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The purpose of this research was to correlate the applied material properties of stretch film with its elastic properties measured in a laboratory setting. There are currently no tools available for a packaging engineer to make a scientific decision on how one stretch film performs against another without applying the film. The system for stretch wrap comparison is mostly based on trial and error which can lead to a significant loss of product when testing a new film or shipping a new product for the first time. If the properties of applied stretch film could be predicted using a tensile test method, many different films could be compared at once without actually applying the film, saving time and money and reducing risk.
The current method for evaluating the tensile properties of stretch film advises the user apply a hysteresis test to a standard sample size and calculate several standard engineering values. This test does not represent how the material is actually used. Therefore, a new tensile testing method was developed that considers the film gauge (thickness) and its prestretch. The results of this testing method allowed for the calculation of the material stiffness (Bisha Stiffness) and were used to predict its performance in unit load containment.
Applied stretch film is currently compared measuring containment force, which current standards define as the amount of force required to pull out a 15.2cm diameter plate, 10.1cm out, located 25.4cm down from the top and 45.7cm over from the side of a standard 121.9cm width unit load. Given this definition, increasing the amount of force required to pull the plate out can be achieved by manipulating two different stretch film properties, either increasing the stiffness of the film or increasing the tension of the film across the face of the unit load during the application process. Therefore, for this research, the traditional definition of containment force has been broken down into two components. Applied film stiffness was defined as the amount of force required to pull the film a given distance off the unit load. Containment force was defined as the amount of force that an applied film exerts on the corner of the unit load.
The applied stretch film was evaluated using two different methods. The first method used the standard 10.1cm pull plate (same plate as ASTM D 4649) to measure the force required to pull the film out at different increments from the center on the face of the unit load. This measurement force was transformed into a material stiffness and film tension (which were subsequently resolved into containment force). The second, newly developed, method involved wrapping a bar under the film, on the corner of the unit load, and pulling out on the bar with a tensile testing machine. This method allowed for the direct measurement of the containment force and material stiffness. The results indicated that while some statistically significant differences were found for certain films, the material stiffness and containment were relatively consistent and comparable using either method.The use of the Bisha Stiffness to predict the applied stiffness and containment force yielded a statistically significant correlation but with a very low coefficient of determination. These results suggest that while film thickness and prestretch are key variables that can predict applied stiffness and containment force, more research should be conducted to study other variables that may allow for a better. High variability of the predictions observed were caused by the differences in film morphology between the different method of elongation (tensile vs application).
This study was the first that attempted to define and correlate the tensile properties of stretch film and the applied properties of stretch film. From this research many, terms have been clarified, myths have been dispelled, formulas have been properly derived and applied to the data collected and a clear path forward had been laid out for future researchers to be able to predict applied stiffness and containment force from the elastic properties of stretch film.<br>Ph. D.