Academic literature on the topic 'Jumping drops'

AbstractSelf-propelled jumping upon drop coalescence has been observed on a variety of textured superhydrophobic surfaces, where the jumping motion follows the capillary–inertial velocity scaling as long as the drop radius is above a threshold. In this paper, we report an experimental study of the self-propelled jumping on a Leidenfrost surface, where the heated substrate gives rise to a vapour layer on which liquid drops float. For the coalescence of identical water drops, we have tested initial drop radii ranging from 20 to $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}500\ \mu \mathrm{m}$, where the lower bound is related to the spontaneous takeoff of individual drops and the upper bound to gravitational effects. Regardless of the approaching velocity prior to coalescence, the measured jumping velocity is around 0.2 when scaled by the capillary–inertial velocity. This constant non-dimensional velocity holds for the experimentally accessible range of drop radii, and we have found no cutoff radius for the scaling, in contrast to prior experiments on textured superhydrophobic surfaces. The Leidenfrost experiments quantitatively agree with our numerical simulations of drop coalescence on a flat surface with a contact angle of 180°, suggesting that the cutoff is likely to be due to drop–surface interactions unique to the textured superhydrophobic surfaces.

AbstractCoalescing drops spontaneously jump out of plane on a variety of biological and synthetic superhydrophobic surfaces, with potential applications ranging from self-cleaning materials to self-sustained condensers. To investigate the mechanism of self-propelled jumping, we report three-dimensional phase-field simulations of two identical spherical drops coalescing on a flat surface with a contact angle of 180°. The numerical simulations capture the spontaneous jumping process, which follows the capillary–inertial scaling. The out-of-plane directionality is shown to result from the counter-action of the substrate to the impingement of the liquid bridge between the coalescing drops. A viscous cutoff to the capillary–inertial velocity scaling is identified when the Ohnesorge number of the initial drops is around 0.1, but the corresponding viscous cutoff radius is too small to be tested experimentally. Compared to experiments on both superhydrophobic and Leidenfrost surfaces, our simulations accurately predict the nearly constant jumping velocity of around 0.2 when scaled by the capillary–inertial velocity. By comparing the simulated drop coalescence processes with and without the substrate, we attribute this low non-dimensional velocity to the substrate intercepting only a small fraction of the expanding liquid bridge.

The paper proposes a theoretical model for the bouncing of a water drop on a free surface. The motion of a drop in air is described by the usual equations connecting the forces of inertia, gravity, and Stokes (viscosity resistance). The drop is considered spherical with a given surface tension. Numerical calculations were carried out using the same algorithm, but with different initial conditions. Some conditions are set for the droplet disintegration, others for the droplet reflection from the free surface. It is shown that the disintegration of a drop occurs periodically with a decrease in the drop size and an increase in the drop rise height. In the interval between droplet decays, periodic reflection from the free surface occurs with a decrease in the rise height.

The lightweight floor is a popular construction choice in buildings despite its poor low-frequency impact sound performance. This is exacerbated by common human activities, such as walking and jumping, that have high input force levels at low frequencies. Therefore, experimental evaluations of the low-frequency impact sound performance of a wooden lightweight floor are of interest to designers and researchers. The aim of this paper is to explore the use of heel drop for impact sound transfer measurement. An impact force plate has been built to accurately measure the heel-drop forces up to 200 Hz and the performances on two types of floors are evaluated. The heel drop has a higher energy level at low frequencies, resulting in higher coherence and signal-to-noise ratio and hence superior performance in characterizing the floors in the frequency range of below 40 Hz when compared to the impact hammer. Interestingly, in the case of a heel-drop excitation, the first natural frequencies of the floor decrease. It is in contrast to when a human is simply standing on it, which resulted in an increase of the natural frequencies upon impact hammer excitation.

A method for a droplet transportation by jumping a obstacle on piezoelectric substrate is presented, and a device for the droplet transportation is implemented on a 128° yx-LiNbO3 piezoelectric substrate. An interdigital transducer and a reflector are fabricated on the piezoelectric substrate using microelectric technology. Hydrophobic film is coated on the area free of electrodes and a polydimethylsilicone obstacle is mounted on it. A radio frequency signal amplified by a power amplifier is applied to the interdigital transducer to generate surface acoustic wave. When the surface acoustic wave meets with the droplet on the piezoelectric substrate during transportation, part of acoustic wave enegy is radiated into the droplet, leading to internal acoustic streaming. Once the radio frequency signal with appropriate amplitude is suddenly decreased, part of the droplet will jump the obstacle due to interial force. Red dye solution drops are demonstrated for transportation experiments. Results show that a droplet can be transported from one side to another of the obstacle on piezoelectric substrate by help of surface acoustic wave. The presented method is helpful for microfluidic system on a piezoelectric substrate.

In this study, the ellipsoidal soil cave with vertical collapses in the covering karst area is studied. Based on certain assumptions, the mechanical model of karst collapse caused by groundwater drop was established. Then, based on the negative pressure calculation formula of soil cave cavity according to Boyle–Mariotte’s law, the expression of the stability coefficient of the soil cave was proposed. Subsequently, the feasibility of the theoretical formula was verified. The calculation example analyzed the relationship of groundwater parameters and overburden thickness. The results show that when the initial groundwater level is higher than the top of cave, the law between the stability coefficient of soil cave and groundwater drawdown shows the jumping horizontal broken line. Thus, soil cave tends to collapse when the falling groundwater level drops over the vault; when the initial groundwater level ranges from the bottom to the top of the cave body, the stability coefficient and groundwater drawdown show a negative correlation law, the curve is steep at the early stage and then becomes gentle at the latter stage, and the higher the initial groundwater level in the cave is, the greater stability coefficient of soil cave reduces; when the initial groundwater level is lower than the bottom of the cave, the effect of drawdown is limited. In addition, for the small drawdown or low initial groundwater level, the stability coefficient of soil cave first decreases and then increases with the increases in thickness of overburden, and the thinner the overburden is, the greater the drawdown rate is; when the drawdown or the initial groundwater level is higher, the stability coefficient of soil cave positively relates to the thickness of the overburden layer.

The purpose of the study was to investigate the effects of fatigue on the lower extremity landing strategies of males and females. Twelve recreationally active males (n = 6) and females (n = 6) (nine used for analysis) performed repetitive drop jumps until they could no longer reach 20% of their initial drop jump height. Kinematic and kinetic variables were assessed during the impact phase of all jumps. At initial ground contact, males exhibited greater extension at the hip and knee and less plantar flexion than females. However, females performed more eccentric work during the impact phase of landing. Fatigue resulted in an increased extension at the hip, knee, and ankle for both genders, but did not have an effect on the peak VGRF. Fatigue also resulted in an increase in work performed at the ankle and an approximately equal reduction in work performed at the knee for both genders. Investigation of the peak powers revealed that as a result of fatigue, females utilized a landing strategy in which more energy was absorbed at the knee during the early part of the impact phase. The increased reliance on the knee musculature to dissipate kinetic energy during the impact phase of landing demonstrated by females may be a reason for the commonly seen gender disparities in injury rates. Furthermore, the shift towards energy absorption during the initial part of the impact phase when noncontact injuries are known to occur, exhibited by females, may indicate a greater injury risk for females.
School of Physical Education, Sport, and Exercise Science

INTRODUCTION: The prevalence of ACL injuries is increasing in previous years. One of the most common studied kinematic risk factors related to ACL injuries is a resultant weak, leg axis alignment known as the dynamic knee valgus angle presented during a vertical drop jump [8, 14, 15]. Hewett et. al. concluded that a knee valgus angle was a primary predictor of the mechanism that leads to an ACL rupture [8]. By increasing the excessive knee valgus angle during a two-legged DVJ, an athlete is in turn increasing the possibility of a high knee valgus moment, which can increase the anterior tibial translation as well as the load on the ACL several-fold and the chances for an ACL tear [4]. METHODS: In our study, ten collegiate female participants, including ballet and non-ballet athletes performed two-legged DVJs for 6 different flexor and extensor muscles while digital recordings of knee valgus angle were captured at initial contact and push off with simultaneous collection of EMG data. RESULTS: Results displayed statistical significance for the average valgus angle to estimated GRF ratio for the non-dominant leg at push-off between the ballet and non-ballet athletes (0.8 ± 0.43 vs. 1.8 ± 0.33 degrees/N, p < 0.05). In addition, we also found that the hip extensor activity significantly increased for the non-ballet group and that the lateral thigh CCI noticeably increased for the non-dominant leg for the non-ballet group, which could be indicative of the noticeable difference in the biceps femoris muscle activation for the non-ballet group when comparing sports type. In addition, statistically significant interactions between sports type and leg type for vastus medialis and gluteus maximus were produced. Observed results also indicated that there was an increase in overall variability for the dominant leg of the non-ballet athletes amongst all studied muscles and for the non-dominant leg for the ballet group specifically studying the gluteus maximus muscle activity. DISCUSSION: Relatively, the non-ballet group could be at a higher risk for increase in femoral adduction, hip adduction, and tibial external rotation, and overall predict a larger knee valgus moment; therefore, the non-ballet group could potentially be at a higher risk for an ACL injury than the ballet group. In addition, there is potential in continued research of neuromuscular differences between ballet and non-ballet athletes to further investigate the vastus medialis and the gluteus maximus muscle activations as well as to investigate the knee valgus moment values.

ABSTRACT Effect of Warm-Up Activity on Vertical Ground Reaction Forces in Basketball Players During Drop Jump Landings Jacob Hinkel-Lipsker Purpose: The purpose of this study was to examine the effect of certain warm-up activities on vertical ground reaction forces (GRFv) during a drop jump landing. Methods: Eight women and twelve men (mean age 22.6 ± 1.82 years) completed three warm-up activities on three separate days in a counterbalanced order: a passive stretching warm-up, a dynamic warm-up, and a no warm-up control. After completing each activity, participants were asked to perform eight drop jump landings on a force platform. GRFv data was sampled at 1000 Hz during each landing, and the variables analyzed were: peak forefoot and rearfoot magnitude, forefoot and rearfoot rate of loading, and impulse. Results: The dynamic warm-up had significantly greater values (p < 0.05) for forefoot peak magnitude, rearfoot peak magnitude, and forefoot rate of loading compared to the passive stretching and control conditions. Also, there were no significant differences among all activities for rearfoot rate of loading and impulse. Conclusions: The significantly greater values for forefoot peak magnitude, rearfoot peak magnitude, and forefoot rate of loading that the dynamic warm-up produced indicates that this activity may be effective in increasing muscular stiffness in the lower limbs. The failure of the passive stretching warm-up to reach significance indicates that this activity may not be effective in decreasing lower extremity muscular stiffness.

Thesis (MScPhysio)--Stellenbosch University, 2014.
ENGLISH ABSTRACT: Introduction: Chronic groin injuries are common among athletes and have the potential to lead to chronic and career-ending pain. There is no evidence available whether pelvic kinematics can be perceived as a risk factor in developing chronic groin pain in sport or be the cause of further injuries of the lower quadrant or lumbar spine. Objective: The purpose of this study was to determine if there are any differences in pelvic kinematics of active sports participants with chronic groin pain compared to healthy controls during a single-leg drop-landing. Methodology: A descriptive study was conducted. The three-dimensional (3D) pelvic kinematics of ten cases with chronic groin pain and ten asymptomatic controls was analyzed. Pelvic kinematics was analyzed at the FNB 3D Vicon Laboratory at Stellenbosch University using an eight camera Vicon system. A physical examination, including functional movements, posture analysis, hip, knee and ankle passive range of motion measurements, sacro-iliac tests and anthropometric measurements was done by two physiotherapists prior to the 3D analysis. To analyze the pelvic kinematics, each participant performed six single-leg drop-landings. The main outcome measure was 3D pelvic kinematics at initial foot contact (IFC) and foot contact at lowest vertical position (LVP). The following sub-groups were analyzed: seven with unilateral groin pain and three with bilateral groin pain; the latter was further divided into those with the most painful leg and the least painful leg. Mean and standard deviations (SD) for pelvic kinematics were calculated and significant differences between sub-groups were determined using two-tailed Student’s t-tests. The Cohen’s D effect size calculator was used to calculate the effect size of significant differences in pelvic kinematics between case and control groups. Results: The findings indicated a significant difference (p=0.03) in frontal plane pelvic kinematics at IFC for the unilateral group. The most painful groin group showed significant differences at IFC (p=0.004) and at LVP (p=0.04) in the frontal plane pelvic kinematics. The least painful groin group showed a significant difference at LVP (p=0.01). All cases landed with pelvic downward lateral tilt during the landing phase compared to matched controls. The groin pain group with bilateral pain showed significant differences at IFC (p < 0.001) and LVP (p=0.005) for the most painful groin; and the least painful groin at IFC (p=0.01) and LVP (p=0.01) in the sagittal plane pelvic kinematics. The bilateral groin pain group showed an increase of anterior pelvic tilt in the sagittal plane during the landing phase when compared to matched controls. Increased internal pelvic rotation in the transverse plane was significant for the unilateral group at IFC (p=0.04) and for the most painful groin group at IFC (p < 0.001) and LVP (p < 0.001) compared to matched controls. Conclusion: Results from this study shows that pelvic kinematic changes in the frontal, sagittal and transverse planes do occur in patients with chronic groin pain when compared to controls. This may imply that muscle weakness around the hip and pelvis may contribute to the development of chronic groin pain in active sports participants. Rehabilitation of these muscles should be taken into consideration when treating patients with chronic groin injuries. Further research should be focused on muscular recruitment patterns in sports participants with groin pain to critically define the muscular causal factors in more depth.
AFRIKAANSE OPSOMMING: Inleiding: Kroniese lies beserings is ‘n algemene verskynsel onder die aktiewe sport populasie. Dit mag tot kroniese pyn lei en het die potensiaal om ‘n sport loopbaan te be-eindig. Tans, is daar geen verdere navorsing beskikbaar oor die invloed van bekken kinematika op onderste ledemaat beserings asook die moontlike oorsaak tot kroniese lies pyn in atlete nie. Oogmerk: Die doel van hierdie studie was om vas te stel watter verskille in die bekken kinematika ontstaan tussen aktiewe sport deelnemers met kroniese lies pyn teenoor aktiewe sport deelnemers sonder enige pyn of beserings tydens ‘n enkel been aftrap beweging. Metodologie: Tien deelnemers met kroniese lies pyn en tien asimptomatiese deelnemers is gebruik om die verskille tussen die 3D bekken kinematika te bepaal. Die FNB 3D Vicon Lab by die Stellenbosch Universiteit is gebruik vir die data analise en insameling. Deelnemers het ‘n fisiese ondersoek ondergaan wat die voglende ingesluit het: funksionele bewegings, postuur analise, omvang van beweging van die heup, knie en enkel, toetse ter uitsluiting van die ilio-sakrale gewrig asook antropometriese aftmetings. Elke deelnemer is versoek om ses enkel-been aftrap sessies te doen. Die hoof uitkomsmeting was die bekken hoeke in the frontale vlak by inisiële voet kontak (IVK) asook die voet kontak teen die laagste vertikale posisie (LVP). Resultate: Die resultate wys ’n beduidende verskil (p=0.03) in die frontale vlak vir bekken kinematika by IVK vir die unilaterale groep. Die mees geaffekteerde been wys ’n beduidende verskil by IVK (p=0.004) en by LVK (p=0.04) in die frontale vlak vir bekken kinematika. Die groep met die minste geaffekteerde been toon ’n beduidende verskil by LVP (p=0.01). Alle simptomatiese deelnemers het met die bekken in afwaartse bekken kanteling geland tydens die landings fase. Die groep met bilaterale pyn toon ’n beduidende verskil by IVK (p < 0.001) en by LVP (p=0.005) vir die mees geaffekteerde been en vir die minste geaffekteerde been by IVK (p=0.01) en LVP (0.01) in die sagittale vlak vir bekken kinematika. Die bilaterale groep met kroniese lies pyn land met meer anterior bekken kanteling in die sagittale vlak gedurende die landings fase teenoor die asimptomatiese groep. Interne bekken rotasie was beduidend meer vir die unilaterale groep by IVK (p=0.04) en vir die mees geaffekteerde been by IVK (p < 0.001) en LVP (p < 0.001) teenoor asimptomatiese deelnemers. Gevolgtrekking: Die resultate van hierdie studie bewys dat daar wel ‘n verskil is in die bekken kinematika van deelnemers met kroniese lies pyn teenoor asimptomatiese deelnemers. Hierdie verskille is waarneembaar in die frontale, sagittale en transverse vlakke. Dit impliseer dat spier swakheid van die bekken en heup spiere ‘n bydrae mag he tot die ontwikkeling van kroniese lies beserings in atlete. Rehabilitasie van bogenoemde spiere is belangrik in die behandeling van kroniese lies beserings. Verdere navorsing oor spier aktiverings patrone in aktiewe, sports deelnemers met kroniese lies pyn word benodig, om die oorsprongs faktore te ondersoek.

Thesis (MScPhysio)--Stellenbosch University, 2014.
ENGLISH ABSTRACT: Chronic groin pain is widespread across many sporting disciplines. The aim of our research was to determine if there are kinematic differences of the thoracic spine in active sports people with chronic groin pain, compared with healthy controls. A cross-sectional descriptive design was followed. Participants were required to complete six single leg drop landings with each leg from a 20cm height. The study was done in the 3D Movement Analysis Laboratory at the University of Stellenbosch. Ten male participants with unilateral or bilateral chronic groin pain of more than 3 months duration and 10 asymptomatic males, matched for age and sports participation, were recruited. The main outcome measures were: thoracic spine angle at initial foot contact, maximum thoracic spine angle, range of movement (ROM) (difference between the minimum and maximum values) and thoracic spine angle at lowest vertical point of the pelvis. This was assessed in all 3 movement planes: the sagittal plane (X plane), the coronal plane (Y plane) and the transverse plane (Z plane). The results of our study showed that for the unilaterally affected groin pain group, the cases landed in significantly more thoracic flexion (P<0.001 with large effect size) and were in significantly more thoracic flexion still at the lowest point. Peak thoracic flexion was significantly more in the cases than the controls. (P<0.001 with medium effect size) The same was true for the bilaterally affected group when landing on the most painful side, although this was not statistically significant. There were no significant differences in the frontal or transverse planes. In the bilaterally painful group, axial rotation ROM was significantly reduced when landing on either leg (worst affected side: P=0.040 with medium effect size and least affected side: p=0.006 with large effect size). The same occurred in the unilaterally affected group, although this was not statistically significant. Our study suggests that, in participants with chronic groin pain, there is greater thoracic forward flexion away from neutral during landing and that total axial rotation ROM during landing is diminished.
AFRIKAANSE OPSOMMING: Kroniese liespyn kom dikwels en in verskeie sportsoorte voor. Die doel van ons studie was om te bepaal of daar kinematiese verskille van die torakale werwelkolom is in aktiewe sportmense met chroniese liespyn, in vergelyking met gesonde kontroles. ‘n Dwars-deursnit beskrywende studiemetode is gevolg, en uitgevoer in die 3D Beweging Analise Laboratorium, Universiteit van Stellenbosch. Deelnemers moes ses landings op een been doen, met elke been, vanaf 'n 20cm hoogte. Tien mans met eensydige of bilaterale chroniese liespyn vir langer as 3 maande, en 10 asimptomatiese mans (ooreenstemmende ouderdom en sport deelname) het deelgeneem. Die hoof uitkomste wat gemeet is, was torakale werwelkolom krommingshoek by aanvanklike voet-kontak, maksimum torakale werwelkolom krommingshoek, omvang van beweging (OVB) (verskil tussen die minimum en maksimum waardes) en torakale werwelkolom krommingshoek by die laagste punt van die bekken. Dit is beoordeel in al 3 beweging vlakke: die sagittale (X) vlak, die koronale/frontale (Y) vlak en die transversale (Z) vlak. Die resultate van die studie het getoon dat, in die eensydig-geaffekteerde liespyn groep, die deelnemers in beduidend meer torakale fleksie geland het(P < 0.001, met 'n groot effekgrootte), asook met aansienlik meer torakale fleksie by die laagste punt na landing. Piek torakale fleksie was aansienlik meer in die liespyn-gevalle as in die kontroles. (P < 0.001, met middelmatige effekgrootte ) Dieselfde het vir die bilateraalgeaffekteerde groep gegeld wanneer hulle op hul mees pynlike kant geland het, hoewel dit nie statisties beduidend was nie. Daar was geen betekenisvolle verskille in die frontale of transversale vlakke van beweging nie. In die bilateraal pynlike groep, was aksiale rotasie OVB aansienlik verminder wanneer die gevalle op hul pynlikste been óf op hul minder pynlike been geland het ( mees pynlike been : P = 0,040, met 'n middelmatige effekgrootte en minder pynlike been : p = 0,006, met 'n groot effekgrootte ). Dieselfde het in die eensydig-geaffekteerde groep gebeur, hoewel dit nie statisties beduidend was nie. Ons studie dui daarop dat, in deelnemers met chroniese liespyn, daar meer torokale fleksie weg van neutraal tydens landing is en dat die totale aksiale rotasie OVB tydens die landing verminder is, in vergelyking met die kontrolegroep.

Thesis (MScPhysio)--Stellenbosch University, 2014.
ENGLISH ABSTRACT: Aims: This study aims to ascertain if there are differences in ankle kinematics and ground reaction force in sports participants with chronic groin pain compared to healthy controls. Methods: A cross sectional descriptive study design was used. Twenty participants - 10 cases with chronic groin pain and 10 healthy controls participated. The 10 cases included participants with unilateral pain (n=7) and bilateral pain (n=3). For analysis, the bilateral pain group was divided into the most and less painful side. The study was conducted at the FNB 3D Motion Analysis Laboratory, Stellenbosch University. Sagittal plane kinematics and VGRF was analysed during a single leg drop landing. Results: The group with unilateral groin pain had a higher peak force compared to the matched side of the controls. The bilateral pain groups had less plantarflexion at foot contact (most affected p=<0.001; least affected p=<0.001) and total range of motion (p=<0.05) compared to the control group. The bilaterally injured groin pain groups demonstrated less peak force when compared to controls. Conclusion: This is the first study to indicate alterations in ankle kinematics and VGRF and that these changes are more apparent in sports participants with bilateral pain. Less range of motion during the landing task illustrated by the bilateral pain group suggests less effective force absorption of the distal segments. In the bilateral groups it suggests that force attenuation may have occurred high up the kinetic chain which may place more strain on the groin. Clinically rehabilitation of the athlete with chronic groin pain should include the distal segments of the lower limb. Further research should be conducted in larger groups.
AFRIKAANSE OPSOMMING: Doelstellings: Hierdie studie poog om vas te stel of daar verskille in enkelbeweging en grondvloer-reaksiekrag is in deelnemers van sport met chroniese liespyn in vergelyking met gesonde kontrole deelnemers. Metode: ‘n Deursnee beskrywende studieontwerp is gebruik. Twintig deelnemers, 10 gevalle met chroniese liespyn en 10 gesonde kontrole het deelgeneem. Die 10 gevalle het ingesluit deelnemers met eensydige pyn (n=7) en bilaterale pyn (n=3). Vir die analise, is die bilaterale pyngroep verdeel in die mees en mins geaffekteerde kant. Die studie is gedoen by die FNB3D Beweginsanalise-laboratorium, Universiteit van Stellenbosch. Sagitaal-platvlak kinematiek en vertikale reaksiekrag is geanaliseer gedurende ‘n enkele beenlanding. Resultate: Die groep met eensydige liespyn het ‘n hoër piekkrag gehad in vergelyking met dieselfde kant van die kontrolegroep. Die bilaterale pyngroep het minder plantaarfleksie met voetkontak getoon (mees geaffekteer p=<0.001; minste geaffekteer p=<0.001) en totale beweginsomvang (p=<0.05) in vergelyking met die kontrolegroep. Die bilateraal-liesbeseringsgroep het minder piekkrag getoon in vergelyking met die kontrolegroep. Gevolgtrekking: Hierdie is die eerste studie om veranderings in enkelbeweging en grondreaksiekrag aan te toon, asook dat hierdie veranderinge meer opvallend is in persone wat aan sport deelneem wat bilaterale pyn ondervind. Verminderde beweginsomvang gedurende die landingstaak deur die bilaterale pyngroep suggereer minder effektiewe kragabsorpsie van die distale segmente. In die bilaterale groep suggereer dit dat kragvermindering waarskynlik hoog op die kinematiese ketting voorgekom het wat weer meer stremming op die lies plaas. Kliniese rehabilitasie van die atleet met chroniese pyn behoort die distale segmente van die onderste ledemaat in te sluit. Verdere navorsing behoort in groter groepe uitgevoer te word.

Thesis (MScPhysio)--Stellenbosch University, 2014.
ENGLISH ABSTRACT: Introduction: Groin injuries are among the top six injuries in contact sports and may lead to career ending chronic pain. Research on the role of knee kinematics in developing chronic groin pain in sport is scarce. Objective: The purpose of this study was to determine if there are differences in knee kinematics during a single-leg drop-landing in sports participants with chronic groin pain compared to asymptomatic controls. Methodology: A descriptive study was conducted. Twenty active sports’ participants were recruited from soccer and rugby clubs situated around the Cape Peninsula area, Western Cape, South Africa. The three-dimensional (3D) knee kinematics of ten cases with chronic groin pain and ten asymptomatic controls was analysed. Knee kinematics was analysed in the FNB-3D Vicon Laboratory at Stellenbosch University, using an eight camera Vicon system. A positive adductor squeeze test was used as a diagnostic test to include cases with chronic groin pain. Each participant performed six single-leg drop landings. The main outcome measure was 3D knee kinematics at initial foot contact and at the lowest vertical position of the drop landing. The following sub-groups were analysed: seven unilateral groin pain cases compared to their seven matched controls; three bilateral groin pain cases where their most painful leg and least painful leg were compared to their matched controls, respectively. Descriptive statistical techniques were used for all outcome measures; means and standard deviations (SD) were calculated, followed by a Student’s t-test to determine significant differences between the cases and controls. For all outcomes with p-values equal to or below 0.05, the effect size was calculated using the Cohen’s D. Results: The findings of this study indicated a significant difference (p=0.0001) between cases with unilateral groin pain having less knee internal rotation compared to the controls at the lowest vertical position of the drop landing in the transverse plane. Significantly less internal rotation (p<0.0001), was also noted in the cases with bilateral groin pain (in the most painful leg and the less painful leg), although this was noted at foot contact. Cases with bilateral groin pain also had significantly (p<0.001) more knee varus (adduction) during the landing phase. Conclusion: Differences in knee kinematics between sports participants with chronic groin pain and asymptomatic controls were found. These findings imply that the knee joint should be included during assessment and rehabilitation of individuals suffering with chronic groin pain. Due to the cross-sectional study design of the current study, it cannot be stated for certain whether the knee kinematics noted in the groin pain group are causative or as a result of groin pain. Future prospective studies are thus recommended; these studies should focus on the effect of contralateral knee kinematics on the hip adductors and may include exploration of the muscular components during a single-leg drop landing.
AFRIKAANSE OPSOMMING: Inleiding: Lies beserings is een van die top ses beserings in kontak sport en kan lei tot chroniese lies pyn en selfs die be-eindigging van ‘n sportloopbaan. Navorsing oor die rol van knie kinematika in die ontwikkeling van chroniese liesbeserings in sport is skaars. Doelwit: Die doel van hierdie studie was om te bepaal of daar verskille in die knie kinematika is tydens 'n enkel been val landing in sport deelnemers met chroniese lies pyn in vergelyking met gesonde kontroles. Metode: 'n Beskrywende studie was uitgevoer. Twintig aktiewe sport deelnemers is gewerf van rugby en sokker sportklubs geleë rondom die Kaapse Skiereiland, Wes-Kaap, Suid-Afrika. Die 3D knie kinematika van tien gevalle met chroniese lies pyn en tien asimptomatiese bypassende kontroles is ontleed. Knie kinematika was ontleed in die FNB-3D Vicon Laboratorium by die Universiteit van Stellenbosch, met behulp van 'n agt-kamera Vicon stelsel. 'n Positiewe Adduktor druk toets was gebruik as 'n diagnostiese toets om gevalle met chroniese lies pyn in te sluit. Om die knie kinematika te analiseer, het elke deelnemer ses enkel been val landings uitgevoer . Die belangrikste uitkomsmeting was 3D knie kinematika by die aanvanklike voet kontak en by die laagste vertikale posisie van die enkel-been val landing. Die volgende sub-groepe was ontleed: sewe unilaterale lies pyn gevalle in vergelyking met hul sewe bypassende kontroles; drie bilaterale lies pyn gevalle waar hul mees pynlike been, sowel as minder pynlike been onderskeidelik vergelyk was met hul bypassende kontroles. Beskrywende statistiese tegnieke was gebruik vir alle uitkoms maatreëls; gemiddeldes en standaardafwykings (SA) was bereken, gevolg deur 'n Studente’s t-toets om beduidende verskille tussen die gevalle en kontroles te bepaal. Vir al die uitkomste met p-waardes gelyk of onder 0.05, is die effekgrootte bereken deur die Cohen’s D. Resultate: Die bevindings van hierdie studie dui op 'n beduidende verskil (p=0,0001) tussen gevalle met unilaterale lies pyn met minder interne knie rotasie in vergelyking met die kontroles by die laagste vertikale posisie van die val landing in die dwars vlak. Aansienlik minder interne rotasie (p<0,0001), is ook opgemerk in gevalle met bilaterale lies pyn (in die mees pynlike been en die minder pynlik been), alhoewel tydens voet kontak. Gevalle met bilaterale lies pyn het ook betekenisvol (p <0.001) meer knie varus (adduksie) tydens die landingsfase gehad. Gevolgtrekking: Verskille bestaan in die knie kinematika tussen sport deelnemers met chroniese liesbesering pyn en gesonde kontroles. Hierdie bevindinge impliseer dat die knie behoort ingesluit te word tydens die assessering en rehabilitasie van individue met chroniese lies pyn. As gevolg van die deursnee-studie ontwerp van hierdie studie, kan dit nie bevestig word of die knie kinematika die oorsaak van die chroniese pyn is nie. Toekomstige voornemende studies word dus aanbeveel, hierdie studies moet fokus op die effek van die kinematika van die kontralaterale knie op die heup adduktore en kan moontlik die ondersoek van die spier kinetika tydens hierdie aktiwiteit insluit.

Thesis (MScPhysio)--Stellenbosch University, 2014.
ENGLISH ABSTRACT: Introduction-Groin injuries are among the top six most cited injuries in soccer and account for 10-18 per cent of all injuries reported in contact sport. Groin pain can result from a variety of pathologies, but according to literature, 63 per cent of groin pain is due to adductor pathology. Objective-The objective of this study was to explore if there are kinematic differences in the hip joint in sports participants with groin pain compared to matched healthy controls. Study design A cross sectional, descriptive study was conducted. Study setting-The study was conducted at the FNB -3D motion analysis laboratory at the University of Stellenbosch, South Africa. Outcome variables-The dependent variables included hip kinematics in the sagittal, frontal and transverse planes at foot strike, lowest vertical point of the pelvis and total range of hip motion during a single leg drop landing. Methodology-The study sample comprised 20 male club level soccer-and, rugby players, running and cycling participants between the ages of 18-55 years of age. Ten of the subjects had chronic groin pain and the other ten were healthy matched controls. An eight-camera Vicon system was used to analyse the kinematics of the hip joint during single leg drop landing. For the purpose of comparison, the data was analysed for participants with unilateral groin pain and matched controls (n=14) and participants with bilateral groin pain and controls (n=6). The full set of data was subdivided for analysis into three distinct sub-groups. Unilaterally injured groin cases (n=7) were matched with seven healthy controls for analysis. Bilaterally injured groin cases (n=3) were matched with three healthy controls. Results-Cases with unilateral groin pain at initial contact had significantly more abduction of the hip joint when compared to controls (p<0.05). The effect size of this difference was large (0.94). Cases with unilateral groin pain also demonstrated greater hip internal rotation while the controls had external rotation (p<0.05) during a drop landing activity. Bilaterally injured groin cases landed with significantly (p=?) greater ranges of hip flexion as well as in significantly (p=?) more hip abduction during a drop landing activity. They also demonstrated greater total range of motion in the frontal plan when compared to controls. Groin pain cases overall demonstrated greater ranges of motion and tended to land in more abduction compared to controls. Conclusion-This study found that during a single leg drop landing, sports participants with unilateral chronic groin pain landed with significantly greater hip abduction and exhibited larger total range of motion in the transverse plane, which may indicate impaired stability of the hip complex when compared to controls.
AFRIKAANSE OPSOMMING: Inleiding-Liesbeserings is een van die top ses mees prominente sokker beserings. Dit beloop 10-18 persent van alle beserings wat in kontaksport aangemeld word. Liespyn kan die gevolg wees van ‘n verskeidenheid patologië, maar volgens die literatuur is 63 persent van liespyn as gevolg adduktor patologie. Doelwitte-Die doelwit van hierdie studie was om ondersoek in te stel of daar enige kinematiese veranderinge in die heupgewrig is in spelers met liespyn in vergelyking met dieselfde vergelykbare spelers sonder liespyn. Studie Ontwerp-‘n Deursnit, beskrywende studie was onderneem. Studie Omgewing-Die studie was uitgevoer by die FNB-3D bewegingsanalise laboratorium van die Stellenbosch Universiteit, Suid-Afrika. Uitkomsveranderlikes-Die afhanklike veranderlikes het in gesluit die heup kinematika in die sagitale, frontale en transvers vlakke met voet kontak endie laagste vertikale punt van die pelvis sowel as die totale heup omvang van beweging gedurende een been landing. Metodologie-Die studie populasie het bestaan uit 20 manlike sokker- en, rugbyspelers, hardlopers en fietsryers tussen die ouderdomme van 18 en 55 jaar. Tien van die deelnemers het kroniese liespyn gehad en die ander tien in die gelyke gesonde groep was sonder liespyn. Die agt kamera Vicon sisteem was gebruik om die kinematika van die heupgewrig te analseer tydens een been landing. Vir die doel om ‘n vergelyking te kan maak, was die data geanaliseer van deelnemers met unilaterale liespyn en die vergelykende groep sonder liespyn (n=14) en deelnemers met bilaterale liespyn en hulle vergelykende groep sonder liespyn (n=6).. Die volledige stel data was onderverdeel in drie afsonderlike sub groepe. Vir die analiese was unilaterale liesbeserings (n=7) vergelyk met sewe deelnemers sonder liespyn in die kontrolegroep. Deelnemers met bilaterale liesbeserings (n=3) was vergelyk met drie in die kontrolegroep. Resultate-Die deelnemers met unilaterale liespyn het met eerste kontak beduidend meer abduksie van die heupgewrig gehad in vergelyking met die kontrolegroep (p<0.05). Die effek van hierdie verskil was groot (0.94). Die deelnemers met unilaterale liespyn het ook ‘n grooter interne rotasie getoon, terwyl die kontrole groep meer eksterne rotasie gedemonstreer het (p<0.05) met landing. Deelnemers met bilaterale liespyn het beduidend (p=?) meer heup fleksie en abduksie omvang van beweging tydens landing. Hulle het ook ‘n groter totale heup omvang van beweging in die frontale vlak gehad in vergelyking met die kontrolegroep. Deelnemers met liespyn het oor die algemeen ‘n grooter omvang van beweging getoon, en was geneig om met meer abduksie van die heup te land as die kontrolegroep. Gevolgtrekking-Die studie toon dat deelnemers met kroniese unilaterale liespyn, tydens een been landing, beduidende meerheup abduksie toon en dat die heup in die transverse vlak meer totale omvang van beweging gebruik wat kan dui op onstabiliteit in die heupkompleks in vergelyking met die kontrolegroep.

The article presents results of the research on jumping strategies applied by elite athletes in various sport disciplines. Research hypothesis: to perform the same motor task athletes employ different ways of organizing the movement and different features of MTU functioning. The choice of a mechanism to enhance muscle contraction depends on sport discipline, in particular specific features of the sport movement. The study involved members of the Russian national teams in alpine skiing, bobsleighing, mogul skiing and ski jumping. The athletes performed drop jumps from the heights of 0.1, 0.3, and 0.5 m with no arm swing. Experimental data were obtained online from 24 cameras using the Qualisys motion capture system (400 frames per second) and the two force plates AMTI 6000. Data was processed using the OpenSim package. The authors calculated the amount of accumulation and utilization of elastic strain energy and assessed metabolic energy expenditures in MTU. The authors concluded that employment of different strategies of movement organization in drop jumps could be explained by the transfer of motor skills specific to the athlete’s sport discipline. The results of the study may help coaches develop individual training plans for athletes, in particular strength training exercises targeting specific muscle groups.

The behaviour of humans jumping on flexible structures has become a matter of some importance for both structural integrity and also human tolerance. The issue is of great interest for stadia, footbridge and floor structures. A test rig has been developed for exploring the forces, accelerations and displacements that occur when a human subject jumps on a flexible structure where motion can be perceived. In tests reported earlier, it was found that the human is able to generate near resonant response of the structure but it was extremely difficult, if not impossible, to jump at or very near to the natural frequency of the structure when the structural vertical motion is significant. Also, the force developed by the subject was found to drop significantly near resonance. In this paper, the effect of the subject-to-structure mass ratio and the damping ratio of the structure on the ability of the subject to jump near resonance, and on the force drop out, is presented. It is shown that as the structure becomes more massive and more highly damped it moves less for nominally the same jumping excitation. In this situation, it becomes easier to jump near resonance and the degree of force drop out reduces, though it is still significant.

The spontaneously jumping motion of condensed droplets by coalescence on superhydrophobic surfaces has been an active area of research due to its great potential for enhancing the condensation efficiency. Despite a considerable amount of microscopic observations, the interfacial wetting characterization during jumping-droplet condensation is still notably lacking. This work focuses on applying a novel acoustic sensor - quartz crystal microbalance (QCM), to characterize the interfacial wetting on nanostructured surfaces during jumping-droplet condensation. Copper oxide nanostructures were generated on the surface of QCM with a chemical etching method. Based on the geometry of the nanostructures, we modified a theoretical model to reveal the relationship between the frequency shift of the QCM and the wetting states of the surfaces. It was found that the QCM is extremely sensitive to the penetrated liquid in the structured surfaces. Then, the QCM with nanostructured surface was tested on a customed flow condensation setup. The dynamic interfacial wetting characteristics were quantified by the normalized frequency shift of the QCM. Combined with microscopic observation of the corresponding drop motion, we demonstrated that partial wetting (PW) droplets with an about 25% penetrated area underwent spontaneously jumping by coalescence. However, the PW droplets no longer jumped when the penetrated area exceeds 50% due to the stronger adhesion between liquid and the surface. It shows that the characterization of the penetrated liquid in micro/nanostructures, which is very challenging for microscopic observation, can be easily carried out by this acoustic technique.

Abstract This paper studies the effects of cut-corner in the recess vaned casing treatment (RVCT) on the performance of a low-speed axial fan. The solid casing fan and fans with corner-cut RVCT have been simulated respectively. The numerical simulation shows that the introduction of the RVCT and the modification of RVCT cut-corner size bring about obvious changes in fan performance. The RVCT establishes a connection between the RVCT channel and the main flow, contributing to the extra flow circulation in the tip region and resulting in an efficiency penalty for each RVCT configuration. The cut-corner is not necessarily beneficial to the improvement of the stable operating range. With the increase of cut-corner size at the rear wall of RVCT, the improvement of stall margin firstly demonstrates a drop to −8.82% before jumping to over 60%. RVCTs with different cut-corner sizes play different roles in the flow interaction between RVCT channel and main flow, and the stall margin poses a positive relationship with the mass flow passing through RVCT. The size of the cut-corner is responsible for the flow field in RVCT. The RVCT with small cut-corner size functions as a larger blade tip clearance and results in a smaller stall margin than the solid casing fan. Therefore, the size of the cut-corner in RVCT should be large enough to dredge the flow blockage in the tip region and delay the origin of stall.