Tesis sobre el tema "Maximal voluntary contraction"

The ability to fully activate the motor units of the quadriceps femoris muscle when performing an isometric maximal voluntary contraction (MVC) was assessed in 30 subjects. The twitch interpolation technique (TIT) was used to measure the increase in force superimposed on the MVC by a supramaximal shock to the femoral nerve. The superimposed force was compared to the potentiated twitch (PtP) force, and an activation ratio (A.R.) was calculated. The resting twitch (PtR) force, MVC force, and the inverse relationship between the level of voluntary force and the superimposed twitch force were also measured. Subjects were compared on the basis of activity level (15 sedentary and 15 trained) and gender (14 males and 16 females). The mean A.R. was 95% regardless of activity level or gender. Males were stronger than females but there was no difference in strength between the sedentary and trained groups. PtR and PtP force values showed the same pattern of results. The nature of the relationship between the level of voluntary force and the superimposed twitch force was curvilinear, and indicates that the TIT may not be accurate in measuring the amount of activation for a muscle as large as the quadriceps when voluntary contractions greater than 70% of the MVC are performed. The intra-subject reliability of the TIT used in this lab was acceptable (ICC = 0.78).

Human motor control is a complex process involving both central and peripheral components of the nervous system. Type Ia afferent input contributes to both motor unit recruitment and firing frequency, however, whether maximal force production is dependent on this input is unclear. Therefore, chapter 2 examined maximal and explosive force production of the knee extensors following prolonged infrapatellar tendon vibration; designed to attenuate the efficacy of the homonymous Ia afferent-α-motoneuron pathway. Despite a marked decrease in H-reflex amplitude, indicating an attenuated efficacy of the Ia afferent-α-motoneuron pathway, both maximal and explosive force production were unaffected after vibration. This suggested that maximal and explosive isometric quadriceps force production was not dependent upon Ia afferent input to the homonymous motor unit pool. Voluntary movements are linked with various modulations in ongoing neural oscillations within the supraspinal sensorimotor system. Despite considerable interest in the oscillatory responses to movements per se, the influence of the motor parameters that define these movements is poorly understood. Subsequently, chapters 3 and 4 investigated how the motor parameters of voluntary contractions modulated the oscillatory amplitude. Chapter 3 recorded electroencephalography from the leg area of the primary sensorimotor cortex in order to investigate the oscillatory responses to isometric unilateral contractions of the knee-extensors at four torque levels (15, 30, 45 and 60% max.). An increase in movement-related gamma (30-50 Hz) activity was observed with increments in knee-extension torque, whereas oscillatory power within the delta (0.5-3 Hz), theta (3-7 Hz), alpha (7-13 Hz) and beta (13-30 Hz) bands were unaffected. Chapter 4 examined the link between the motor parameters of voluntary contraction and modulations in beta (15-30 Hz) oscillations; specifically, movement-related beta decrease (MRBD) and post-movement beta rebound (PMBR). Magnetoencephalography (MEG) was recorded during isometric ramp and constant-force wrist-flexor contractions at distinct rates of force development (10.4, 28.9 and 86.7% max./s) and force output (5, 15, 35 and 60%max.), respectively. MRBD was unaffected by RFD or force output, whereas systematic modulation of PMBR by both contraction force and RFD was identified for the first time. Specifically, increments in isometric contraction force increased PMBR amplitude, and increments in RFD increased PMBR amplitude but decreased PMBR duration. Physical fatigue arises not only from peripheral processes within the active skeletal muscles but also from supraspinal mechanisms within the brain. However, exactly how cortical activity is modulated during fatigue has received a paucity of attention. Chapter 5 investigated whether oscillatory activity within the primary sensorimotor cortex was modulated when contractions were performed in a state of physical fatigue. MEG was recorded during submaximal isometric contractions of the wrist-flexors performed both before and after a fatiguing series of isometric wrist-flexions or a time matched control intervention. Physical fatigue offset the attenuation in MRBD observed during the control trial, whereas PMBR was increased when submaximal contractions were performed in a fatigued state.

The present study investigated the effects of transcranial direct current stimulation (tDCS) on maximal voluntary contraction strength (MVC) and the time to failure (TTF) of an isometric muscle endurance test of the elbow flexors. Prior to the main study, the test-retest reliability of MVC and TTF measures was investigated using 10 men (33.2 ± 9.4 y) for the measurements separated by 60 min (within-day) and one week (between-day). Coefficient of variation (CV), Intraclass correlation (ICC, R), a paired t-test and the Bland-Altman plots revealed that TTF at 30% MVC task was reliable, and was able to detect a possible effect of tDCS on TTF, if the magnitude of effect was greater than 11%. Based on the reliability study results, it was hypothesised that tDCS would increase TTF from the first test to the second test separated by 60 min, when a tDCS treatment was administered immediately before the second test. Fifteen men (27.7 ± 8.4 y) were tested for MVC and TTF at 30%-MVC before and immediately after tDCS or sham intervention (10 min) in three separate sessions. In two sessions direct current (2 mA) was delivered through saline-soaked sponge electrodes, with the anode placed on the scalp overlying the right motor cortical representation of the left arm and the cathode secured over the right shoulder. One session was a sham intervention (current delivery for the first 30s). The order of the intervention sessions was randomised and counterbalanced amongst the subjects and subjects who were blinded to intervention type. Changes in MVC strength and TTF from pre to post intervention were compared between the interventions by a two-way repeated measures ANOVA. No significant differences were evident for the two tDCS sessions. MVC strength (baseline: 66.0 ± 11.4 Nm) decreased by 5.9 ± 4.2 % (P

Muscle can generate greater force with lower muscle activation during eccentric (ECC) than isometric (ISO) and concentric (CON) contractions (actions). Unaccustomed ECC exercise induces muscle damage represented by prolonged impairment of muscle function and delayed onset muscle soreness (DOMS), but also confers protection from muscle damage, known as the repeated bout effect (RBE). However, the neuromuscular characteristics of ECC contractions, and the mechanisms involved in the muscle damage and RBE induced by ECC are not fully understood. Therefore, the purpose of this PhD thesis was to examine the neuromuscular characteristics of ECC contractions of the knee extensors in relation to muscle damage and the RBE profiles. This thesis consisted of five studies as summarised below. Study 1: Short-interval intracortical inhibition (SICI) is often used to examine inhibitory responses in the primary motor cortex representation of the quadriceps, but appropriate pairedpulse transcranial magnetic stimulation (TMS) parameters to optimise SICI measurement were not clear. Using 9 men and 6 women (26.6 ± 4.4 y), responses to single and paired-pulse (3-ms interval) TMS were recorded from vastus lateralis (VL), rectus femoris (RF) and vastus medialis (VM). Test stimulus intensity was 140% of active motor threshold (AMT), and conditioning stimulus intensities (CSIs) ranged from 55-90% (eight intensities) of AMT (5 test and 5 paired responses for each intensity). With CSI of 55% AMT, SICI was minimal (conditioned:test motor evoked potential [MEP]; 1.00, 0.96 and 0.95 for VL, RF and VM, respectively, -1.00 indicates inhibition). Inhibition was greater at 70-90% AMT for VL (0.67- 0.85), at 75-90% AMT for RF (0.70-0.78) and at 80-90% AMT for VM (0.59-0.68) when compared to 55% AMT. The CSIs that elicited maximal and 50% maximal inhibition were ~84% and ~75% AMT, respectively. This method was shown to provide a practical approach to investigate quadriceps inhibitory networks. Study 2: Responses to TMS, twitch forces (TF) and voluntary drive were compared between ECC, ISO and CON contractions of the knee extensors. Sixteen participants (20-33 y) performed submaximal and maximal voluntary contractions (MVCs) for ISO and isokinetic (30˚/s) CON and ECC of knee extensors. EMG was recorded from VL. Supramaximal femoral nerve stimulation during and after MVCs evoked superimposed (ST) and resting TF to calculate voluntary activation (VA). Maximal M-waves (MMAX) were recorded. During 30% MVCs, single- and paired-pulse TMS elicited MEPs and assessed SICI. MVC torque was greater (P Study 3: ECC-only and coupled concentric-eccentric contractions (CON-ECC) of the knee extensors were compared for changes in neurophysiological indices before, immediately after and 1-3 days post-exercise. Twenty participants (19-36 y) were randomly assigned to ECC (n=10) or CON-ECC (n=10) group. ECC group performed 6 sets of 8 ECC-only contractions at 80% of ECC one-repetition maximum (1-RMecc), while CON-ECC group performed 6 sets of 8 alternating CON and ECC (i.e., 8 CON and 8 ECC) contractions at 80% of CON 1-RM and 1-RMecc, respectively. Maximal voluntary isometric contraction (MVIC) force, rate of force development (RFD), TF elicited by femoral nerve stimulation, VA, MEPs, corticospinal silent period (CSP) and SICI assessed by single- and paired-pulse TMS, and muscle soreness were measured before, immediately after, and 1-3 days post-exercise. No significant (p>0.05) differences between ECC and CON-ECC were evident for the changes in any variables post3 exercise. MVIC force decreased immediately post-exercise compared to baseline (ECC: -20.7 ± 12.8%, CON-ECC: -23.6 ± 23.3%) and remained low at 3 days post-exercise (-13.6 ± 13.4%, -3.3 ± 21.2%), and changes in RFD were greater than those of MVIC force (immediately postexercise: ECC: -38.3 ± 33.9%, CON-ECC: -30.7 ± 38.3%). VA, TF and MEP/MMAX decreased and CSP increased post-exercise (p Study 4: Since the participants from Study 3 responded similarly for indirect indicators of muscle damage, the 20 participants were used to examine whether the magnitude of muscle damage indicated by changes in MVIC force 1-3 days after ECC could be predicted by changes in central and peripheral neuromuscular parameters immediately post-ECC. The criterion measures were the same as those in Study 2, and additional analyses of the rate of force development (RFDRT) and rate of relaxation (RRRT) of the TF were performed. Relationships between changes in the variables immediately post-ECC and changes in MVIC force at 1-3 days post-ECC were examined by Pearson product-moment (r) or Spearman correlations. MVIC force decreased (-22.2 ± 18.4%) immediately post-exercise, and remained below baseline at 1 (-16.3 ± 15.2%), 2 (-14.7 ± 13.2%) and 3 days post-ECC (-8.6 ± 15.7%). Immediately post-ECC, RFD (0-30-ms: -38.3 ± 31.4%), TF (-45.9 ± 22.4%), RFDRT (-32.5±40.7%), RRRT (-38.0±39.7%), VA (-21.4 ± 16.5%) and MEP/MMAX at rest (-42.5 ± 23.3%) also decreased, while CSP at 10%-MVIC increased by 26.0 ± 12.2% (p Study 5: Among the 20 participants described in Study 4, 10 participants (6 from the eccentriconly exercise group and 4 from the concentric-eccentric exercise group) returned two weeks after the first exercise bout to perform the second bout of the same exercise. Changes in MVIC force, RFD, muscle soreness, TF, VA, MMAX, MEPs, and SICI before, immediately after and 1–3 days post-exercise were compared between the first (ECC1) and the second bouts (ECC2). ECC2 induced less (P=0.01) muscle soreness (peak: 27.5 ± 26.6 mm) than ECC1 (50.7 ± 31.8 mm), and MVIC force decreased more immediately post-ECC1 (-21.6 ± 23.3%) than ECC2 (-11.0 ± 11.3%) and recovered faster to the baseline after ECC2 than ECC1. RFD decreased immediately after ECC1 (e.g. 0-50-ms: -50.5 ± 52.5%, P0.05). The non-significant differences in VA and MEPs between ECC1 and ECC2, and lack of changes in MMAX and SICI suggest that changes in neural factors after eccentric exercise do not explain the repeated bout effect. Collectively, these studies advance understanding of the characteristics of ECC muscle contractions and their relationship to muscle damage and the RBE, and can be used to inform future research directions.

L’objectif de ce travail était de comparer l’importance de la composante nerveuse dans les différences de production de force entre les enfants et les adultes en tenant compte des conditions mécaniques qui sont susceptibles de l’influencer (longueur musculaire, mode et vitesse de contraction) et des effets de la fatigue. Trente et un garçons pré-pubères de 8-12 ans et 37 hommes de 18-30 ans ont été recrutés et répartis dans les 3 études composant ce projet. La première étude portait sur les effets de la longueur musculaire et de la fatigue sur la production de force et le niveau d’activation maximal volontaire (VA) des extenseurs du genou.La seconde traitait des effets de la longueur musculaire sur la production de force et le VA des fléchisseurs plantaires. Enfin, la troisième portait sur les effets du mode et de la vitesse de contraction sur le VA des extenseurs du genou. Les propriétés neuromusculaires ont été évaluées à l’aide de stimulations magnétiques périphériques et de contractions maximales volontaires. Les résultats montrent un VA des extenseurs du genou supérieur chez l’adulte lors de grande longueur musculaire (90°-100° de flexion) (étude 1), mais aucune différence avec l’enfant à courte longueur musculaire (20° de flexion). En revanche, sur des groupes musculaires tels que les fléchisseurs plantaires, aucun effet de la longueur sur le VA n’a été observé chez les enfants et les adultes (étude 2). En ce qui concerne les effets du mode de contraction, nos résultats montrent que le VA est inférieur en conditions excentrique et concentrique par rapport à la condition isométrique, mais aucune différence n’était observée entre les groupes (étude 3). Toutefois, l’effet de cette baisse de VA sur la production de force variait entre les groupes ; une diminution de force accompagnant la diminution de VA n’était retrouvée que chez l’adulte. Enfin,nous avons montré que la baisse du VA au cours d’un protocole de fatigue est plus conséquente chez les enfants par rapport aux adultes (étude 1), ce qui témoigne de l’existence d’une fatigue centrale majorée chez l’enfant. Une maturation inaboutie et les propriétés musculo-tendineuses particulières de l’enfant (compliance supérieure) pourraient expliquer les résultats obtenus au cours de ce travail
The purpose of this PhD thesis was to compare the contribution of the maximal voluntary activation level (VA) of the motor units to force production differences between children and adults in various mechanical conditions that affect force production (muscle length, contraction mode and velocity), and in fatigue condition. Thirty one pre-pubertal 8 to 12-year old boys and 37 men (18-30 years) were recruited and allocated into the 3 studies ofthis project. The first study was devoted to compare the effects of muscle length and fatigue on the VA and force generating capacity of the knee extensors between children and adults. In the second study, we compared the effects of muscle length on the VA and force generating capacity of the plantar flexors between children and adults. The third study analysed the effect of contraction mode and velocity on the VA and force generating capacity of the knee extensors between children and adults. Neuromuscular properties were assessed with peripheral magnetic stimulation and maximal voluntary contractions. Results showed a higher VA of the knee extensors in adults at long muscle length (90° and 100° knee flexion) but no difference between children and adults at short length (20° knee flexion; study 1). However, the VA of the plantar flexors was not affected by muscle length changes whatever the age group considered (study 2). Results also showed a higher VA in isometric mode compared to eccentric and concentric conditions whatever the age group (study 3). However, the effect of this VA reduction on force generating capacity differed between groups, a concomitant force reduction being observed in adults, but not in children. Finally, we observed a greater VA reduction and therefore greater central fatigue in children during the fatiguing protocol (study 1). A relative immaturity and the particular musculo-tendinous properties of children (higher compliance) may account for the reported results

L'objectif de ce travail de thèse est d'étudier d'une part les spécificités de la commande nerveuse lors de la contraction excentrique en explorant les mécanismes impliqués au niveau spinal et d'autre part d'examiner les mécanismes nerveux responsables de la plasticité du système neuromusculaire après un entraînement de force excentrique sous-maximal. A travers ce travail de thèse, nous mettons en évidence la contribution de l'inhibition récurrente à la réduction de l'activation musculaire classiquement observée lors de la contraction excentrique. Par ailleurs, nous montrons que l'inhibition récurrente est majorée lors des contractions sous-maximales indépendamment du mode de contraction. Ces résultats soulignent le rôle important de l'inhibition récurrente dans la spécificité de la commande nerveuse lors de la contraction excentrique. Nous confirmons que le pilotage nerveux de la contraction excentrique peut être modulé par l'entraînement de force excentrique même si les modulations de l'excitabilité spinale semblent dépendre des caractéristiques de l'entraînement
The purpose of this PhD research is, on the one hand, to study the neural drive specificities during eccentric contractions by exploring the neural mechanisms involved at spinal level and, on the other hand, to examine the neural mechanisms responsible for the modulations of neuromuscular system following a strength submaximal eccentric training. Through this PhD research we highlight the contribution of recurrent inhibition by the Renshaw cell to the decrease of muscular activation typically observed during eccentric contraction. Furthermore, we show that recurrent inhibition is enhanced during submaximal contractions regardless of the contraction type. These results emphasize the important role of recurrent inhibition in the specificity of neural control during eccentric contractions. We confirm that the neural drive of the eccentric contraction may be modulated by eccentric strength training although modulations of spinal excitability seem to depend on the characteristics of training

Electrical muscle stimulation (EMS) is widely used in rehabilitation and sport training, and alternating current and pulsed current EMS are commonly used. However, no systematic comparison between alternating and pulsed current EMS has been made in the previous studies. The main aim of this research was to compare acute physiological responses between the alternating and pulsed current EMS. The secondary purpose of the research was to investigate further muscle damage induced by EMS-evoked isometric contractions. Three experimental studies were conducted in the thesis project together with literature review about EMS.

Darbo objektai – 1) skirtingiems fiziniams krūviams adaptuotų sportininkų maksimalios valingos jėgos įtaka greitumo jėgos rodikliams. 2) krepšininkų parengimas taikant skirtingus treniruočių modelius. Keliame hipotezes, kad turintys didesnę maksimalią valingąją jėgą tiriamieji greičiau bėgs 30 m distancijos pirmą atkarpą (0-10 m.), o adaptuoti maksimaliajam bėgimo greičiui – greičiau bėgs nuotolio pabaigoje ir pasieks geresnius rezultatus. Taikant koncentruotą treniruočių sistemą didelio meistriškumo krepšininkai pasiekia geresnių galingumo rodiklių ir sugeba juos išlaikyti rungtynių metu. Tikslai Nustatyti taikytų skirtingų treniravimo modelių įtaką judamųjų gebėjimų ugdymui. Uždaviniai: 1. Nustatyti ir palyginti skirtingam fiziniam krūviui adaptuotų sportininkų maksimalios valingosios jėgos (MVJ) ir 30 m bėgimo rezultatus bei bėgimo greičio prieaugio tempą. 2. Nustatyti ir palyginti vertikalaus šuolio rezultatus krepšininkų grupėms, besitreniruojančioms pagal skirtingus treniruočių modelius. Išvados: 1. Turėdami didžiausią MVJ pirmus 10 m greičiausiai įveikia sunkiaatlečiai, tačiau likusias bėgimo atkarpas greičiausiai įveikia elito sprinteriai, taip pat pasiekdami didžiausią bėgimo greičio prieaugį nuo 10 iki 30 bėgimo metro – 29,74 % (p<0,05). 2. Koncentruotas skirtingų judamųjų gebėjimų ugdymo modelis labiau pagerina krepšininkų vertikalaus šuolio rezultatus bei jų atsistatymą po rungtynių nei mišraus režimo modelis. Praktinės rekomendacijos: tyrimo metu gauti duomenys... [toliau žr. visą tekstą]
The objects of the study: 1) the impact of maximum voluntary contraction force to speed values for the athletes who are adapted to different physical loads. 2) the physical preparation of the basketball players using different training models. It is possible to make a hypothesis that athletes who have greater maximum voluntary contraction force runs faster in the first 10 meters (0-10 meters.) in the distance of 30 meters. However, the sprinters who are adapted to maximum speed of running runs faster in the end of the distance and achieves better results. Applying concentrated training model, the results of professional basketball players achieve greater power indicators and are able to keep them during the mach. The aim – To identify the influence of the different training models applied to the training of the moving abilities. Scopes: 1. To identify and compare the maximal voluntary contraction force and 30 meters of running results. Although to identify and compare the rate of increment for the speed of running. 2. To identify and compare the rates of vertical leap for the groups of basketball players who are trained using different training models. Conclusions: 1. Weightlifters who have the greatest maximum voluntary contraction force pass the first 10 meters faster. However, the other meters of the distance are passed faster by elite sprinters. In addition, the elite sprinters achieve the greatest increment of running speed (from 10 to 30 running meter – 29.74 % (p<0.0... [to full text]

It is well known that maximal eccentric exercise induces muscle damage, especially when it is performed for the first time. However, muscle damage is attenuated in subsequent bouts of the same or similar exercise, which is known as the repeated bout effect. One of the factors affecting the magnitude of muscle damage and the repeated bout effect is the number of eccentric contractions; however, it is unknown if different set-repetition configurations with the same number of eccentric contractions would result in different magnitudes of muscle damage and adaptation. This study investigated changes in muscle strength, range of motion (ROM), muscle cross sectional area (CSA), muscle soreness and plasma creatine kinase (CK) activity following an initial bout of maximal eccentric contractions with the same total number of contractions but different set-repetition configurations (e.g. 3 sets of 10 reps vs. 10 sets of 3 reps) and a second bout (20 sets of 3 repetitions) separated by four weeks. Since the present study was the first to use the ultrasound extended field of view (EFOV) technique to quantify bicep brachii CSA for an indication of muscle swelling, the reliability and validity of the technique were assessed in a separate study using 6 men (27.5 ± 1.9 y). In the main study, 10 non-resistance trained men (26.1 ± 4.1 y) performed two bouts of eccentric exercise of the elbow flexors for each arm (4 bouts in total). One arm performed 3 sets of 10 maximal eccentric contractions (3x10) followed 4 weeks later by 20 sets of 3 maximal eccentric contractions (20x3). The contralateral arm performed 10 sets of 3 maximal eccentric contractions (10x3) followed 4 weeks later by 20x3. The order of the exercise (3x10, 10x3) and the use of arm (dominant, non-dominant) were counterbalanced amongst subjects. Changes in the criterion measures over time and peak torque were compared among the initial bouts (3x10 vs. 10x3) and the repeated bouts (20x3 vs. 20x3) by a factorial repeatedmeasures analysis of variance (ANOVA) with two factors. Significance level was set at P

L'objectif de ce travail était de déterminer i) l'influence du niveau de force absolue sur la durée du temps de maintien, et les altérations neuromusculaires subséquentes chez un même individu à l'issue d'un exercice réalisé à la même intensité relative, avec un ou deux membres ; ii) l'influence de la commande nerveuse sur la capacité de production de force de chacun des muscles extenseurs du genou lors de contractions unilatérales (UL) vs. bilatérales (BL); iii) l'évolution des mécanismes d'activation pendant une série de contractions sous-maximales évoquées par électromyostimulation (EMS).Les résultats de la première étude confirment que le temps limite est dépendant du niveau de force absolu pour un même individu, la durée de la contraction en UL étant 20% plus longue qu'en BL. De plus, une corrélation a été trouvée entre la force lors d'une contraction maximale volontaire (CMV) et le temps limite en UL et BL. Toutefois, d'autres mécanismes semblent être également mis en jeu, car dans un cas les mécanismes sont d'origine nerveux et musculaire (UL), alors que dans l'autre cas les mécanismes sont seulement nerveux (BL). Les résultats de la deuxième étude montrent que la force maximale développée lors d'une contraction BL est inférieure à la somme des forces des contractions UL (i.e. présence d'un déficit bilatéral). Les temps d'apparition des pics de force lors des CMV de chacune des jambes ne sont pas différents de celui de la CMV BL, mais la force développée au cours de celle-ci est inférieure à la somme des CMV de chacune des jambes durant la CMV BL, c'est-à-dire à la force maximale produite par chacune des jambes lors de la CMV BL. Néanmoins, aucune différence d'activité EMG, d'amplitude d'onde M, de doublet et de niveau d'activation n'a été observée entre les conditions UL et BL. Les résultats de la troisième étude montrent que l'estimation de la commande descendante, par la technique de la secousse surimposée, lors d'un effort sous-maximal fatigant présente des biais méthodologiques. Toutefois, l'estimation des mécanismes nerveux par les deux méthodes classiques (niveau d'activation volontaire (NAV) et ratio d'activation centrale (CAR)) reste néanmoins pertinente pendant des contractions maximales volontaires. L'ensemble de nos travaux met en évidence l'intervention de mécanismes d'origine nerveux différents entre les contractions UL et BL

This thesis examined the thermoregulatory and neuromuscular responses to passive heating in 42 °C hot water. The data suggest that hot-water immersion at 42 °C is an efficient, safe and tolerable method for passive heating therapy. Moreover, a single session of hot-water immersion can increase rapid force production and improve muscle contractile function. Findings from this thesis indicate that passive heating via hot baths may improve physical function in the older and patient populations and assist healthy people during sports injury recovery.

O objetivo desse estudo foi verificar a relação da aptidão aeróbia e de fatores neuromusculares com o desempenho em SR em tenistas com diferentes níveis de jogo. Um grupo de dez tenistas profissionais (GP) e um grupo de dez tenistas amadores (GA) foram submetidos a quatro sessões experimentais, a saber: 1) medidas antropométricas, familiarização com o teste de drop jump (DJ) e com o teste de contração voluntária isométrica máxima (CVIM) para membros inferiores, e um teste progressivo até a exaustão; 2) um teste de DJ e um teste de carga constante para avaliar a cinética on e off do consumo de oxigênio (VO2); 3) um teste de CVIM para membros inferiores, outro teste de carga constante para avaliar a cinética on e off do VO2 e familiarização com o teste de SR; 4) um teste composto por dez SR. O GP apresentou valores significativamente menores para o tempo do melhor sprint (SRmelhor) e para a média dos tempos de todos os sprints (SRmédio) em relação ao GA (p < 0,05). O percentual de aumento do tempo ao longo dos sprints (SR%aumento) do GP não foi significativamente menor em comparação ao GA (p = 0,102), porém a chance dessa variável ser menor para o GP foi considerada \"provável\". Para o GP, a única correlação significativa observada foi entre o SRmédio e o tempo de contato obtido no teste de DJ (r = 0,641, p < 0,05). Em relação ao GA, foram observadas correlações significativas da velocidade pico obtida no teste progressivo até a exaustão com o SRmelhor (r = -0,680, p < 0,05) e SRmédio (r = -0,744, p < 0,05), assim como da amplitude da fase lenta da cinética off do VO2 com o SRmelhor (r = -0,756, p < 0,05) e SRmédio (r = -0,794, p < 0,05). Portanto, esses dados sugerem que tenistas profissionais possuem um melhor desempenho em SR em comparação aos tenistas amadores. Entretanto, não está clara a importância de fatores da aptidão aeróbia e neuromusculares no desempenho dessa atividade
The objective of this study was to verify the relationship of aerobic fitness and neuromuscular factors with RS performance in tennis players with different playing level. A group of ten professional (PG) and ten amateur (AG) tennis players were submitted to four experimental sessions, to know: 1) anthropometric measurements, familiarization with the drop jump (DJ) test and the maximal voluntary isometric contraction (MVIC) test for the lower limbs, and a progressive test until exhaustion; 2) a DJ test and a constant load test for on and off oxygen consumption (VO2) kinetics measurement; 3) a MVIC test for the lower limbs, another constant load test for on and off VO2 kinetics measurement, and familiarization with the RS test; 4) a test of ten RS. The PG presented significant lower values for the best sprint time (RSbest) and mean time of all sprints (RSmean) in relation to the AG (p < 0.05). The percentage increase in time over all sprints (RSincrease) of the PG was not significantly lower in comparison to the AG (p = 0.102), however the chance of this variable to be lower for the PG was considered \"probable\". For the PG the only significant correlation observed was between RSmean and the contact time obtained in the DJ test (r = 0.641, p < 0.05). In relation to the AG, significant correlations were observed for the peak speed obtained on the progressive test until exhaustion with the RSbest (r = -0.680, p < 0.05) and RSmean (r = -0.744, p < 0.05), likewise for the amplitude of the slow phase in oxygen uptake off-kinetics with the RSbest (r = -0.756, p < 0.05) and RSmean (r = -0.794, p < 0.05). Thus, these data suggest that professional tennis players have a better performance in RS compared to amateur tennis players. However, it is not clear the importance of aerobic fitness and neuromuscular factors in the performance of this activity

Many clinicians believe exercise associated muscle cramps (EAMC) occur because of dehydration and electrolyte losses. Experimental research supporting this theory is lacking. Mild hypohydration (3% body mass loss) does not alter cramp threshold frequency (TF), a measure of cramp susceptibility, when fatigue and exercise intensity are controlled. No experimental research has examined TF following significant (3-5% body mass loss) or serious hypohydration (>5% body mass loss). TF and blood variables of ten subjects were measured pre-post exercise. Subjects exercised in an environmental heat chamber alternating between upper arm ergometry and non-dominant leg cycling every 15 minutes until they lost 5% of their body mass or were too exhausted to continue. Significant (n=5) or serious hypohydration (n=5) did not alter cramp TF, cramp intensity, or cramp EMG amplitude. Significant and serious hypohydration with moderate electrolyte losses does not alter cramp susceptibility when fatigue and exercise intensity are controlled.

The purpose of the present study was to investigate the acute effects of local vibration on muscle performance at different durations and frequencies. Fifteen male handball players participated in the study voluntarily. University&rsquo
s Ethics Committee approved the study and the informed consent forms were filled by all participants. Different vibration durations, (10 sec, 1 min, 10 min), different frequencies (40 and 80 Hz), dominancy (dominant and non-dominant) and conditions (vibration and no-vibration) were independent variables of study. Dependent variables were maximum isometric strength measures under different situations. One way Repeated measures ANOVA, Bonferoni adjusted paired sample t-tests and Two way Repeated ANOVA was used for statistical analyses. Result of this study demonstrated that local vibration (LV) induced significantly higher muscle activity than no vibration (NV) condition. Strength improvements were obtained in quadriceps muscles of dominant and non-dominant legs for 40 Hz and 80 Hz. When 40 Hz vibration was applied to dominant leg with different durations (10 sec, 1 min, 10 min), significantly higher strength measures were found than no vibration. When 80 Hz vibration was applied to dominant leg with different durations (10 sec, 1 min, 10 min), only 10-sec vibration duration revealed significant increase in strength measures. When 40 Hz vibration was applied to non-dominant leg with different durations, (10 sec, 1 min, 10 min) significantly higher strength measures were found than no vibration. When 80 Hz vibration was applied to non-dominant leg with different durations (10 sec, 1 min, 10 min), 10-sec and 1 min vibration durations revealed significant increase in strength measures. However, no significant difference was obtained when the different vibration durations were compared between 40 Hz and 80 Hz.

This study is a subset of a larger body of research that examined shoulder time to fatigue during overhead work in an attempt to reduce the prevalence and impact of work-related musculoskeletal problems in the shoulder associated with overhead work, particularly during automobile assembly. Existing evidence suggests that shoulder injuries are diverse in terms of tissues affected and symptoms presented. Furthermore, the cause of these injuries is multifactorial. The work presented here assumes that musculoskeletal injuries of the shoulder mechanism are at least related to, if not caused by, fatigue localized to the shoulder musculature. While the exact relationship between fatigue and injury has not been clearly established, there is consensus among researchers that fatigue plays and important role. Muscular fatigue, therefore, is viewed as a surrogate measure of risk, and task design to avoid fatigue is seen as a rational method to minimize this risk. An experiment to determine the effects of tool weight on shoulder fatigue and performance during overhead work with work/rest cycles was performed. Times to fatigue were derived based on dependent measures including total task duration, controlled maximum muscle contractions, subjective ratings based on Borg's CR-10 RPE scale, electromyogram behavior (MdPF), and hand force performance measures. Experimental findings indicated that duty cycle (percentage of total task cycle time spent working) significantly affected task duration (p<0.0001), changes in maximum voluntary contraction values for the infraspinatus (p<0.05), and the minimum time for any shoulder muscle to fatigue as determined by changes in the EMG power spectrum (p<0.05). Time to fatigue for the mid deltoid as determined by changes in the median frequency of the EMG power spectrum was shown to change significantly (p<0.05) with change in tool weight. Large intersubject variation was observed for the dependent measures, which showed subjects experiencing different levels of fatigue while performing the same task. Limitations of the study and recommendations for future direction are also discussed.
Master of Science

Electric muscle stimulation (EMS) has been widely used in the rehabilitation of musculoskeletal injuries. Patterned electrical neuromuscular stimulation (PENS), a specific form of EMS, has been developed to better educate muscles to contract properly. The physiological efficacy of PENS has not been quantifiably identified. OBJECTIVES: The aim of this study is to determine the acute effect of one PENS training session (3 sets of 10 1-sec repetitions) on maximal isometric knee extensor (MVIC) torque production and surface EMG (sEMG) in healthy nonathlete college students. DESIGN: A randomized repeated-measures design was used in this study. METHODS: Twenty-two male college students participated in the study. All participants completed two training sessions, one with PENS and one without, in a randomized crossover design. RESULTS: One bout of PENS training significantly increased MVIC (3.1% ± 1.7%, p = 0.03) which was greater than the change in MVIC of the control group (p = 0.03). Control training did not alter MVIC but resulted in significant decrease in average sEMG amplitude (-7.8% ± 1.6%, p ≤ 0.01) and peak sEMG amplitude (-10.4% ± 2.7%, p ≤ 0.01). These reductions in sEMG following control training were significantly different from the PENS group (p = 0.03 and p ≤ 0.01). CONCLUSIONS: The findings suggest that strength training in conjunction with PENS can enhance torque production after just one bout of training. The increase in torque with no change in sEMG amplitude can be explained by increased motor unit synchronization or decreased cocontraction of antagonist muscles.

Força máxima (TF) e potência (TP) são métodos de treinamento considerados distintos, na prática profissional e em diversos designs experimentais. O presente estudo testou a capacidade destes métodos promoverem o aumento do desempenho, assim como a similaridade das adaptações entre os métodos. Trinta e sete sujeitos foram divididos nos grupos: força (TF), potência (TP) e controle (C), sendo submetidos a oito semanas de treinamento nas seguintes zonas: TF (4-10 RM) e TP (30-60% 1RM). Os resultados significantes foram: força dinâmica máxima TF de 145,3 (±17,1) para 178,5 (±18,8) kg, TP de 147,2 (±16,8) para 171,6 (±19,9) kg; pico de força na contração voluntária isométrica máxima (CVIM) TF de 2240,52 (±448,76) para 2651,82 (±700,22) N, TP de 2249,86 (±427,95) para 2674,80 (±507,68) N; salto vertical a partir da posição de semi-agachamento (SJ) TF de 31,35 (±4,63) para 37,18 (±4,74) cm, TP de 34,44 (±3,90) para 39,61 (±4,70) cm. Apenas o TP gerou aumento no salto com contra-movimento (CMJ) de 35,52 (±4,43) para 38,50 (±4,34) cm. Nenhum dos protocolos promoveu o aumento do sinal eletromiográfico, seja na CVIM ou nos saltos. Verificou-se efeito principal para deslocamento do centro de gravidade, torque de joelho e quadril no SJ, assim como para o deslocamento excêntrico no CMJ. Observou-se similaridade entre os grupos em diversas variáveis analisadas, assim como a possível transferência coordenativa do TP para o CMJ. Assim, força máxima e potência parecem constituir estímulos de treinamento equivalentes em muitos aspectos e por isso, os padrões de especificidade atribuídos a ambos devem ser reconsiderados
Strength and power are considered different training methods in promoting neuromuscular adaptations in practice and in several research designs as well. In the present research, the efficacy of these methods in improving performance and resultant neural adaptations in some motor tasks was investigated. Thirty sevens subjects were divided in groups: strength (TF), power (TP) and control (C) and submited to eight weeks of training in different zones: TF (4-10 RM) and TP (30%-60% 1RM). Results that reached significance were the following, pre and pos-test, respectively: Maximum dynamic strength TF:145,3 (±17,1) and 178,5(±18,8), TP:147,2 (±16,8) and 171,6 (±19,9). Peak force in maximum isometric voluntary contraction (MIVC) TF: 2240,52 (±448,76) and 2651,82 (±700,22), TP: 2249,86 (±427,95) and 2674,80 (±507,68). Squat jump (SJ) TF: 31,35 (±4,63) and 37,18 (±4,74), TP: 34,44 (±3,90) and 39,61 (±4,70). In countermovement jump (CMJ) only TP improved: 35,52 (±4,43) and 38,50 (±4,34). No method could improve electromiographical signal. A main effect was noticed for center of mass displacement, knee and hip moments in SJ and eccentric displacement in CMJ. Similar results for many parameters analysed could be observed. The results indicate a possible transference from TP to CMJ as well. This way, strength and power can be considered equivalent in promoting performance in many tasks. Therefore, specificity patterns between strength and power should be reconsidered

Projeto de Graduação apresentado à Universidade Fernando Pessoa como parte dos requisitos para obtenção do grau de Licenciado em Fisioterapia
Objetivo: Avaliar os efeitos da utilização da crioterapia de corpo inteiro (CCI) na recuperação da força muscular de indivíduos fisicamente ativos. Metodologia: Pesquisa computorizada foi realizada nas bases de dados Pubmed/Medline, PEDro, Lilacs, Scielo, Web of Science e Cochrane Library foi efetuada usando a combinação: (whole body cryotherapy OR cryogenic chamber therapy OR cryotherapy OR cryostimulation) AND (delayed onset muscle soreness OR muscle damage OR muscle strenght OR maximum voluntary contraction OR DOMS) de acordo com guias de PRISMA. Apenas estudos randomizados controlados foram incluídos do estudo. Estudos foram analisados usando a Physiotherapy Evidence Database scoring scale (PEDro). Resultados: Nesta revisão foram incluídos 5 artigos que cumpriram os critérios de elegibilidade com um total de 81 participantes e com média aritmética de 6/10 na escala de PEDro. Apesar de não haver consenso sobre os efeitos da CCI na recuperação da força muscular, foram encontrados resultados estatisticamente significativos em vários parâmetros de avaliação. Conclusão: Os resultados não são conclusivos sobre o facto da CCI promover uma melhor recuperação da força muscular de indivíduos fisicamente ativos, comparativamente com outras modalidades de crioterapia ou grupo placebo.
Objective: To evaluate the effects of using whole-body cryotherapy (WBC) on the recovery of muscle strength of physically active individuals. Methodology: Computerized research was performed in the databases Pubmed/Medline, Science Direct, PEDro, Lilacs, Scielo, Web of Science and Cochrane Library was performed using the combination: (whole body cryotherapy OR cryogenic chamber therapy OR cryotherapy OR cryostimulation) AND (delayed onset muscle soreness OR muscle damage OR muscle strenght OR maximum voluntary contraction OR DOMS) according to PRISMA guidelines. Only randomized controlled trials were included in the study. Studies were analyzed using the Physiotherapy Evidence Database scoring scale (PEDro). Results: In this review were included 5 articles that fulfilled the eligibility criteria with a total of 81 participants and obtained an arithmetic average of 6/10 on the PEDro scale. Although there is no consensus on the effects of WBC on muscle strength recovery, statistically significant results were found in several assessment parameters. Conclusion: The results are not conclusive about the fact that the ICC promotes a better recovery of the muscular strength of physically active individuals, compared to other types of cryotherapy or placebo group.
N/A

碩士
朝陽科技大學
工業工程與管理系碩士班
98
For industrial tasks involving manual operations, the workers need to generate sutiable grip strength to hold the object or to safely and effectively control and use the hand tools. Previous studies related to grip strength focused on exploring the maximum and submaximum grip strength or maximum enduration time for gripping exertions for bare and gloved hands. However, no literatures were found investigating suitable duration for sampling of consecutive maximum grip strength without fatigue and at the same time acceptable by the subjects. This study use grip dynamometer and electromyography (EMG) module to collect EMG signals for four forearm muscles when performing consecutive maximum gripping exertions for bare and gloved hands using two or four minutes rest period between gripping efforts. Ten males and eight females participated in this experiment. The suitable sampling duration will be the time that 90% of males and 75% of females can perform consecutive MVC gripping exertions without fatigue. Borg 10-point scale was also used to measure the discomfort level during the consecutive maximum gripping exertions. The results show that there were statistically significant differences in maximum grip strength between gloving condition, rest time, and gender. Muscle activities in extensor carpi radialis longus (ECR), extensor digitorum (ED) were also differed significantly between two and four minutes rest period. Based on Joint analysis of EMG spectrum and amplitude (JASA), the subjects can follow the recovery time of 2 minutes of Caldwell’s regimen between consecutive grip exertions for all four gripping conditions without fatigue. However, the average grip strength during the sampling period for 4 minutes rests test are 2.6 ± 0.6 Kg higher than the 2 minutes rest tests. In this study, the suitable sampling duration is defined as the time that the subject can maintain 80% of the maximum grip strength during consecutive maxumum gripping exertions. For each of the four different gripping conditions (bare hand-2 minutes rest, gloved hand-2 minutes rest, bare hand-4 minutes rest, gloved hand-4 minutes rest), the results show that the suitable sampling duration that 90% of males and 75% of females can perform consecutive MVC gripping exertions without fatigue were 17、8、48、38 minutes and 47、32、98、58 minutes, respectively.

Afin d’être représentatif d’un niveau d’effort musculaire, le signal électromyographique (EMG) est exprimé par rapport à une valeur d’activation maximale. Comme l’épaule est une structure articulaire et musculaire complexe, aucune contraction volontaire isométrique (CVMi) proposée dans la littérature ne permet d’activer maximalement un même muscle de l’épaule pour un groupe d’individus. L’objectif de ce mémoire est de développer une approche statistique permettant de déterminer les CVMi optimales afin de maximiser les niveaux d’activation d’un ensemble de muscles de l’épaule. L’amplitude du signal EMG de 12 muscles de l’épaule a été enregistrée chez 16 sujets alors qu’ils effectuaient 15 CVMi. Une première approche systématique a permis de déterminer les 4 CVMi parmi les 15 qui ensemble maximisent les niveaux d’activation pour les 12 muscles simultanément. Ces 4 contractions ont donné des niveaux d’activation supérieurs aux recommandations antérieures pour 4 muscles de l’épaule. Une seconde approche a permis de déterminer le nombre minimal de CVMi qui sont nécessaires afin de produire un niveau d’activation qui n’est pas significativement différent des valeurs d’activation maximales pour les 16 sujets. Pour 12 muscles de l’épaule, un total de 9 CVMi sont requises afin de produire des valeurs d’activation qui sont représentatives de l’effort maximal de tous les sujets. Ce mémoire a proposé deux approches originales, dont la première a maximisé les niveaux d’activation qui peuvent être produits à partir d’un nombre fixe de CVMi tandis que la deuxième a permis d’identifier le nombre minimal de CVMi nécessaire afin de produire des niveaux d’activation qui ne sont pas significativement différentes des valeurs d’activation maximales. Ces deux approches ont permis d’émettre des recommandations concernant les CVMi nécessaires à la normalisation de l’EMG afin de réduire les risques de sous-estimer l’effort maximal d’un ensemble d’individus.
As a means to provide information on the intensity of the muscle activity, the electromyographic (EMG) signal must be expressed as a percentage of a maximum activation value. Because of the anatomical complexity of the shoulder, no single maximum voluntary isometric contraction (MVIC) has been found to maximally activate the same muscle for a group of subjects. The objective of this study is to develop a statistical approach to determine the optimal MVICs that can maximise the activation levels for several shoulder muscles. The amplitude of the EMG signal of 12 shoulder muscles was recorded as 16 subjects performed 15 MVICs in standardised positions. A first systematic approach was used to determine the optimal 4 MVICs amongst 15 that could maximise the activation levels of 12 shoulder muscles simultaneously. The activation levels produced by these 4 MVICs were significantly higher than those produced by previous recommendations. A second approach was adopted to identify the minimum number of MVICs that were required to produce muscle activation levels that did not significantly differ from the maximum activation values. For 12 shoulder muscles, 9 MVICs were necessary to produce muscle activation levels that were representative of the maximum effort of all 16 subjects. This study proposed two novel approaches, the first of which maximised the EMG activation levels that can be produced by a fixed number of MVICs while the second approach identified the minimum number of MVICs required to produce EMG activation levels that were not significantly different from the maximum values of activation. These two approaches provided guidelines with regards to the MVICs that are necessary to normalize the EMG signals of 12 shoulder muscles while reducing the risks of underestimating the maximum capacity of each individual.

碩士
華梵大學
工業管理學系碩士班
93
The objectives of this study were evaluating the effects of lifting posture and belt tightness on maximal volitional contraction (MVC), normalized electromyogram(NEMG) and evaluating the effects of lifting posture, belt tightness and external load on endurance and NEMG and developing the prediction models of endurance based on external load for different lifting posture without belt. To achieve the objectives as above mentioned, three experiments were applied in this study. Twelve male students from Huafan University were recruited. In first experiment, each of twelve subjects was asked to perform twelve different combinations of static lifting (4 lifting posture * 3 belt tightness). The subject’s MVC, NEMGs, HR and rating of perceived exertion (RPE) were monitored. The results displayed that MVC, HR, upper-back RPE and NEMGs (erector spine, rectus femoris and biceps femoris) were significantly affected by lifting posture (p＜0.05). Furthermore, the belt tightness had significant effect on rectus-abdominus NEMG at 30mmHg in statistic, but not in practice. These findings revealed that lifting belt could not improve subjects’MVC. In the second experiment, each of the same twelve subjects had to carry out 36 experimental sessions (4 lifting posture * 3 belt tightness * 3 external load), endurance testing. The subject’s recovery time, endurance, NEMGs, HR, and RPE were measured. The results showed that lifting posture and external load had significant effect on endurance, HR, RPE and NEMG for six muscle groups (p＜0.05). The erector-spine NEMG at 15 mmHg and 30mmHg had no significant difference. It indicated that endurance time was not extended by wearing lifting belt. In third experiment, to develop endurance prediction models, each of all subjects performed 40 endurance tests (4 lifting posture * 10 external load) without lifting belt. The results displayed that the exponential functions were better prediction functions for four lifting posture. The adjusted R of prediction functions ranged from 0.697 to 0.836.