The research described in this thesis examined age- and strength training-related changes in Achilles tendon stiffness and plantarflexor force production in prepubertal children. The measurement of both Achilles tendon stiffness and muscular force production requires in vivo moment arm lengths to be known. Currently, this is possible only by using expensive and time-consuming medical imaging methodologies. Therefore, the predictability of the Achilles tendon moment arm from surface anthropometric measurements was assessed in the first experimental study (Chapter 3). The results demonstrated that a combination of foot length and the distance between the calcaneal tuberosity and 1st metatarsal head could explain 49% of the variability in Achilles tendon moment arm length in 5 – 12 year-old children. This was considered to be unacceptable for further use, thus an ultrasound-based method was decided upon for obtaining moment arm length in subsequent experimental studies. In the second and third experimental studies (Chapters 4 and 5), age-related changes in tendon mechanical and structural properties were documented and their relationship with changes in force production ability were examined in prepubertal children (5 – 12 years) and adult men and women. In Chapter 4, Achilles tendon stiffness was shown to increase with age through to adulthood, and that changes in tendon stiffness were strongly and independently associated with body mass (R2 = 0.58) and peak force production capacity (R2 = 0.51),which may provide the tendon with an increasing mechanical stimulus for growth and microadaptation. These increases in tendon stiffness were associated with a greater increase in tendon CSA (~105%) than that found for tendon length (~60%), in addition to an increase in Young’s modulus (~139%), suggesting that gross increases in tendon size as well as changes in its microstructure underpinned the increase in stiffness. In Chapter 5, the relationships between Achilles tendon stiffness and both electro-mechanical delay (EMD) and rate of force development (RFD) were determined during maximal isometric plantarflexion contractions. Moderate correlations were found between tendon stiffness and both EMD (r = -0.66) and RFD (r = 0.58). RFD was significantly better predicted when muscle activation (estimated as the rate of EMG rise) was included in a regression model. These data clearly show that increases in tendon stiffness with age through to adulthood are associated with decreases in EMD and increases in RFD, and that the rate of muscle activation has an additional influence on RFD during growth. Given that 1) Achilles tendon stiffness was lower in children than adults, 2) this lower stiffness was associated with a longer EMD and slower RFD, and 3) that strength training in adults had previously been shown to increase tendon stiffness and RFD, the adaptability of the developing Achilles tendon to a resistance training programme, and consequence of the potential changes on force production capacity were examined in the final experimental study (Chapter 6). Significant increases in Achilles tendon stiffness and Young’s modulus were found after 10 weeks of twice-weekly plantarflexor strength training in 8-9 year-old boys and girls, which demonstrates that the larger muscle force production provided a sufficient stimulus for tendon microadaptation. The training also resulted in a decrease in EMD, which was moderately correlated with the change in tendon stiffness (r = 55), but no change in RFD. Thus, the increasing tendon stiffness with training was associated with a decreasing EMD, but had no detectable effect on RFD. This would likely have a significant effect on the performance of tasks requiring rapid muscle force production. Together, the results of the present series of investigations demonstrate that the tendon loading experienced from both normal ageing and overloading (strength training) can increase tendon stiffness in children, and that these changes have a detectable effect on rapid force production.

Introduction: Acute enhancements of muscle contractile properties and performance subsequent to a maximal or near maximal conditioning contraction are often termed post activation potentiation (PAP). Although still controversial, PAP is commonly linked to enhancements in the myosin regulatory light chain phosphorylation, leading to improvements in the excitation–contraction coupling. The PAP seen after a conditioning task often coexists with fatigue and is known to depend on strength level, muscle fiber type and age. Less is known about how factors such as static and dynamic changes in muscle length affect PAP, and on the relative contribution of contractile and tensile components to PAP. Aim: To enhance our understanding of how, and under what conditions, a single maximal isometric contraction affects plantar flexor muscle contractile performance, and other muscle tendon properties, in power athletes. Methods: Supramaximal twitches were evoked via electrical stimulation of the tibial nerve of athletes before and on several occasions after a 6-second maximal voluntary isometric contraction (6-s MVIC) in both static muscle, and during passive muscle lengthening and shorting at different angular velocities. Several contractile variables were measured from the twitches. The effects of a 6-s MVIC on Achilles tendon stiffness was calculated from torque and ultrasonography based measurements of tendon length at two submaximal contraction intensities. Overall stiffness index was calculated by analyzing the passive lengthening torque/angle curve.Results: A single MVIC enhanced muscle contractile properties and electromechanical delay for up to 5 minutes. Plantar flexor twitch variables such as peak twitch, rate of torque development and rate of torque relaxation were enhanced during shortening compared to lengthening muscle actions, and in an extended as compared to a flexed knee position. Achilles tendon stiffness and overall stiffness index were not significantly modulated by a single 6-s MVIC. Conclusion: The results of this thesis imply that functional enhancements from a 6-s conditioning MVIC would mainly come from improvements in contractile rather than tensile components. Stiffness changes should be monitored in future PAP-related studies since they may still occur after more extensive conditioning protocols than the current one. Improvements in contractile components subserving muscle strength after a conditioning MVIC suggests that enhancements in muscle power after a conditioning task should be greatest in fast concentric muscle actions, though still present in muscle lengthening. Conditioning should be performed in a position where full activation is easy to achieve and tailored to mach an athlete or group of athlete’s current status and characteristics, maximizing performance in a specific sport event. / <p>The project recived financial support from the Swedish National Centre for Research in Sports (CIF). Paulo Gago also wishes to thank the Fundação para a Ciência e Tecnologia (FCT), Portugal for the Ph.D. Grant (SFRH/BD/103572/2014).</p><p>New version 2015-01-25 updates the previous one by correcting the errors described in the correction list file (errata).</p> / Doctoral project: Post activation potentiation - Modulating factors and mechanisms for muscle performance.

Objective: To examine the influence of a 6-week training program on the electromechanical delay (EMD) and reaction time of the peroneus longus muscle. Design and Setting: The study was guided by a 2 x 2 factorial design with repeated measures on the time factor. The independent variables for this study were group (training and control) and time (pre- and post-training). Dependent variables for this study were muscle reaction time and electromechanical delay of the peroneus longus muscle. Subjects: Thirty-six healthy, physically active, college-age (21.8 ± 2.3 yr) male and female (M = 14, F = 28, height = 173.7 ± 11.2 cm, weight = 69.1 ± 18.4 kg) subjects were recruited for this study. Subjects had experienced no more than one ankle sprain to either ankle in their life, and had not sprained either ankle in the last year. Subjects were not currently experiencing any lower extremity pathology and had no history of serious injury to either lower extremity. Measurements: The EMD of the peroneus longus was determined by the onset of force contribution after a percutaneous electrical stimulation was administered, as measured by EMG and force plate data. Reaction time was measured after a perturbation during walking. Data was analyzed using two 2 X 2 X 2 ANOVAs. Group (treatment and control) and gender were between treatments factors, and time was a within treatments factor. Results: Upon initial examination, there was a trend in the EMD measurements to show an increase in EMD in the treatment group. However, this lacked statistical significance (F = 2.96, p = 0.0983). Reaction time demonstrated a trend towards a decrease in reaction time in the treatment group, but again, this lacked statistical significance (F = 2.88, p = 0.1025). Effect size for this reaction time was 1.2. Conclusions: The 6-week training program used in this study did not have a significant effect on the reaction time and electromechanical delay of the peroneus longus muscle.

Neural activation is thought to be essential for the expression of maximal muscle performance, but the exact contribution of neural mechanisms such as the level of agonist, antagonist and stabiliser muscle activation to muscle strength is not fully understood. Explosive neuromuscular performance, including the ability to initiate (the electromechanical delay, EMD) and develop force rapidly (termed, rate of force development, RFD) are considered essential for the performance of explosive sporting tasks and joint stabilisation and thus injury avoidance. The thesis aimed to improve our understanding of the contribution of neural factors to muscle performance, with a specific focus on explosive neuromuscular performance. The work in this thesis utilised a range of approaches to achieve this aim. Initially, the association between muscle activation and rate of force development and EMD was established. Comparison of unilateral and bilateral actions was then undertaken. Finally interventions with the aim to both negatively affect and improve muscle strength, which included fatigue and resistance training (RT), respectively was undertaken and the neural contributions to changes in performance established. Agonist activation during the early phase of voluntary force production was shown to be an important determinant of voluntary EMD, explaining 41% of its inter-individual variability. Agonist activation was an important determinant of early, but not late phase RFD. Use of bilateral actions resulted in a reduction in explosive strength, which was thought to be due to differences in postural stability between unilateral and bilateral strength tasks. The level of stabiliser activation was strongly related to the level of agonist activation during the early phase of explosive force development and had a high association with explosive force production. Task-specific adaptations following isoinertial RT, specifically, the greater increase in isoinertial lifting strength than maximal isometric strength were due to training-specific changes in the level of agonist activation. High-intensity fatigue achieved a more substantial decline in explosive than maximal isometric strength, and this was postulated to be due to neural mechanisms, specifically decreased agonist activation. This work provides an in depth analysis of the neural contributions to maximal muscle performance.

O objetivo deste estudo foi avaliar e comparar o equilíbrio de força muscular e o tempo de retardo eletromecânico na articulação do ombro entre atletas de diferentes modalidades esportivas, os quais utilizam predominantemente rotações internas e externas de ombro durante as suas práticas esportivas. Fizeram parte do estudo 41 sujeitos do sexo masculino, sendo 15 atletas profissionais de Voleibol (24,07 ± 5,13 anos; 91,60 ± 11,67 kg; 198,47 ± 5,90 cm), 14 atletas profissionais de Judô (26,64 ± 7,30 anos; 87,36 ± 15,20 kg; 178,07 ± 6,90 cm) e 12 atletas universitários de Handebol (23,17 ± 4,70 anos; 84,75 ± 13,50 kg; 182,08 ± 6,20 cm). Para a mensuração de força máxima, de diferença contralateral (i.e. lados direito vs. esquerdo) e para o cálculo das razões entre rotação interna e externa de ombro, os participantes realizaram testes de dinamometria isocinética em condições isométricas e isocinéticas. Durante os testes isométricos foi realizada a coleta do sinal eletromiográfico dos músculos peitoral maior e infraespinal, o que possibilitou o cálculo do retardo eletromecânico. Os resultados demonstram que atletas de Judô possuem força isométrica de rotação interna de ombro significativamente (p<0,01) maior quando comparados com atletas de Voleibol e de Handebol. Atletas de Judô apresentam valores de razão agonista/antagonista isométrica de membro direito significativamente (p<0,03) inferiores aos grupos Voleibol e Handebol, bem como significativamente (p<0,01) inferiores ao grupo Voleibol em relação ao membro esquerdo O tempo de retardo eletromecânico apresentou diferenças entre os grupos somente na rotação externa, em que o grupo Voleibol apresentou valores do membro direito significativamente (p<0,01) mais curtos quando comparados com o grupo Handebol e valores de membro esquerdo significativamente (p<0,01) mais curtos quando comparados com os grupos Handebol e Judô. Picos de torque isocinéticos apresentaram diferença somente para rotação interna de membro direito, em que o grupo Judô apresentou valores significativamente (p<0,001) maiores quando comparados com o grupo Voleibol. Já para membro esquerdo, detectou-se diferença significativa (p<0,01) no ângulo de pico de torque de rotação interna de membro esquerdo entre o grupo Judô e Handebol. Os resultados do estudo permitem concluir que a prática de cada modalidade esportiva avaliada neste estudo promoveu adaptação dos músculos do ombro, de acordo com a demanda da modalidade esportiva. Assim, atletas de Judô necessitam realizar reforço dos músculos rotadores externos do ombro, tanto concêntrica quanto excentricamente, visto o desequilíbrio muscular causado pela especificidade da modalidade. Por outro lado, atletas de Voleibol apresentam satisfatório equilíbrio muscular na articulação do ombro por conta de altos níveis de força excêntrica de rotação externa exigidos na prática deste esporte; além disso, os curtos períodos de tempo de retardo eletromecânico apresentados por estes atletas reforçam a constatação de equilíbrio desta articulação. Atletas de Handebol apresentam satisfatório equilíbrio muscular na articulação do ombro, entretanto apresentam valores altos de retardo eletromecânico, sendo indicado que estes atletas realizem reforço de rotação externa de ombro, sobretudo em velocidade elevada, com o objetivo de diminuir o tempo necessário para ativar estes grupos musculares. / The purpose of this study was to evaluate and compare the muscular balance and the electromechanical delay time of the shoulder joint between athletes of different sports modalities who use predominantly internal and external rotations of the shoulder. The study consisted of a total of 41 male subjects, of whom 15 were professional Volleyball players (n = 15, 24.07 ± 5.13 years, 91.60 ± 11.67 kg, 198.47 ± 5.90 cm), 14 professional Judo athletes (26.64 ± 7.30 years, 87.36 ± 15.20 kg, 178.07 ± 6.90 cm) and 12 university Handball athletes (23.17 ± 4.70 years, 84.75 ± 13.50 kg, 182.08 ± 6.20 cm). To evaluate peak torque, upper limb side-to-side asymmetry and for the calculation of conventional and functional ratios, all subjects performed isokinetic dynamometry tests under isometric and dynamic conditions. During the isomeric tests, the electromyographic signal was collected from the pectoralis major and infraspinal muscles, which allowed the calculation of the electromechanical delay. The results demonstrate that Judo athletes have internal shoulder rotation isometric strength significantly (p<0.01) higher when compared to Volleyball and Handball athletes. Judo athletes presented isometric agonist/antagonist ratio of right limb significantly (p<0.03) lower than the Volleyball and Handball groups, as well as significantly (p<0.01) lower than the Volleyball group in relation to the left limb. The electromechanical delay time presented differences between the groups only in the external shoulder rotation, which the Volleyball group presented significantly lower values of right limb (p<0.01) when compared to the Handball group and left limb times significantly (p<0.01) shorter when compared with the Handball and Judo groups Dynamic peak torque presented difference only for internal shoulder rotation of the right limb, which the Judo group presented values significantly (p<0.001) higher when compared to the Volleyball group. For the left upper limb, a significant difference (p<0.01) was detected in the peak torque angle of internal shoulder rotation between the Judo and Handball groups. The results of the study allow to considering that the practice of each evaluated sports modalities adapts the shoulder of its athletes in different ways. Judo athletes need to perform external shoulder rotation muscular strengthening, both in concentric and eccentric modes due to muscle imbalance caused by the specificity of the modality. Volleyball athletes have reasonable muscle balance in the shoulder joint due to the high levels of eccentric strength of external rotation, in addition the short time periods of electromechanical delay presented by these athletes reinforce even more the balance of this joint. Handball athletes have reasonable muscle balance in the shoulder joint; however, they presented high values of electromechanical delay, so it is indicated that these athletes need to perform muscular strengthening of external rotation of the shoulder in order to reduce the time required to activate these muscles.

The purpose of this investigation was to assess the between-day reliability of selected force-time curve indices and the activity onset of selected neck muscles in the performance of maximal, isometric contractions in five different directions. The measures extracted are deemed important for future investigations aimed at exploring the role of cervical musculature in reduction of concussion occurrences in sports. Twenty eight physically active male participants performed two testing sessions separated by 7-8 days. In each testing session, force and surface electromyography (EMG) data were recorded simultaneously in a custom-made testing apparatus whilst subjects performed four randomized maximal isometric efforts in extension, flexion, and left and right lateral bending and protraction. The variables examined were the peak force, rate of force development (RFD), time to 50% of peak force and bilateral activity onset of the splenius capitis, upper trapezius, and sternocleidomastoid. For all variables, reliability was assessed by: 1) difference scores between the testing sessions and corresponding 95% confidence intervals; 2) standard error of measurement (SEM), expressed in either the original units of measurement, or as a coefficient of variation; and, 3) Intraclass correlation coefficients (ICC). The results indicated that for all variables, in all testing directions, no differences in scores were observed between the first and second testing sessions. The precision of measurement for all measures, barring muscle onsets obtained in protraction, was deemed acceptable for future clinical application. ICC score ranges for force-time curve-based measurements were high (< 0.90), while for muscle onsets, the ICC ranges are low to moderate (0.23 -0.79). Based on these results, it was concluded that, in highly active male participants, a dedicated familiarization session for the elimination of potential learning effects is not required. In addition, for the majority of testing directions, the force-time curve-based variables as well as muscle activity onsets are recorded with a sufficiently high level of precision, which make them prime candidates for utilization in future investigations concerned with quantitative assessment of cervical musculature function. / Thesis (Master, Kinesiology & Health Studies) -- Queen's University, 2009-09-23 01:23:12.324

O objetivo deste estudo foi avaliar e comparar o equilíbrio de força muscular e o tempo de retardo eletromecânico na articulação do ombro entre atletas de diferentes modalidades esportivas, os quais utilizam predominantemente rotações internas e externas de ombro durante as suas práticas esportivas. Fizeram parte do estudo 41 sujeitos do sexo masculino, sendo 15 atletas profissionais de Voleibol (24,07 ± 5,13 anos; 91,60 ± 11,67 kg; 198,47 ± 5,90 cm), 14 atletas profissionais de Judô (26,64 ± 7,30 anos; 87,36 ± 15,20 kg; 178,07 ± 6,90 cm) e 12 atletas universitários de Handebol (23,17 ± 4,70 anos; 84,75 ± 13,50 kg; 182,08 ± 6,20 cm). Para a mensuração de força máxima, de diferença contralateral (i.e. lados direito vs. esquerdo) e para o cálculo das razões entre rotação interna e externa de ombro, os participantes realizaram testes de dinamometria isocinética em condições isométricas e isocinéticas. Durante os testes isométricos foi realizada a coleta do sinal eletromiográfico dos músculos peitoral maior e infraespinal, o que possibilitou o cálculo do retardo eletromecânico. Os resultados demonstram que atletas de Judô possuem força isométrica de rotação interna de ombro significativamente (p<0,01) maior quando comparados com atletas de Voleibol e de Handebol. Atletas de Judô apresentam valores de razão agonista/antagonista isométrica de membro direito significativamente (p<0,03) inferiores aos grupos Voleibol e Handebol, bem como significativamente (p<0,01) inferiores ao grupo Voleibol em relação ao membro esquerdo O tempo de retardo eletromecânico apresentou diferenças entre os grupos somente na rotação externa, em que o grupo Voleibol apresentou valores do membro direito significativamente (p<0,01) mais curtos quando comparados com o grupo Handebol e valores de membro esquerdo significativamente (p<0,01) mais curtos quando comparados com os grupos Handebol e Judô. Picos de torque isocinéticos apresentaram diferença somente para rotação interna de membro direito, em que o grupo Judô apresentou valores significativamente (p<0,001) maiores quando comparados com o grupo Voleibol. Já para membro esquerdo, detectou-se diferença significativa (p<0,01) no ângulo de pico de torque de rotação interna de membro esquerdo entre o grupo Judô e Handebol. Os resultados do estudo permitem concluir que a prática de cada modalidade esportiva avaliada neste estudo promoveu adaptação dos músculos do ombro, de acordo com a demanda da modalidade esportiva. Assim, atletas de Judô necessitam realizar reforço dos músculos rotadores externos do ombro, tanto concêntrica quanto excentricamente, visto o desequilíbrio muscular causado pela especificidade da modalidade. Por outro lado, atletas de Voleibol apresentam satisfatório equilíbrio muscular na articulação do ombro por conta de altos níveis de força excêntrica de rotação externa exigidos na prática deste esporte; além disso, os curtos períodos de tempo de retardo eletromecânico apresentados por estes atletas reforçam a constatação de equilíbrio desta articulação. Atletas de Handebol apresentam satisfatório equilíbrio muscular na articulação do ombro, entretanto apresentam valores altos de retardo eletromecânico, sendo indicado que estes atletas realizem reforço de rotação externa de ombro, sobretudo em velocidade elevada, com o objetivo de diminuir o tempo necessário para ativar estes grupos musculares. / The purpose of this study was to evaluate and compare the muscular balance and the electromechanical delay time of the shoulder joint between athletes of different sports modalities who use predominantly internal and external rotations of the shoulder. The study consisted of a total of 41 male subjects, of whom 15 were professional Volleyball players (n = 15, 24.07 ± 5.13 years, 91.60 ± 11.67 kg, 198.47 ± 5.90 cm), 14 professional Judo athletes (26.64 ± 7.30 years, 87.36 ± 15.20 kg, 178.07 ± 6.90 cm) and 12 university Handball athletes (23.17 ± 4.70 years, 84.75 ± 13.50 kg, 182.08 ± 6.20 cm). To evaluate peak torque, upper limb side-to-side asymmetry and for the calculation of conventional and functional ratios, all subjects performed isokinetic dynamometry tests under isometric and dynamic conditions. During the isomeric tests, the electromyographic signal was collected from the pectoralis major and infraspinal muscles, which allowed the calculation of the electromechanical delay. The results demonstrate that Judo athletes have internal shoulder rotation isometric strength significantly (p<0.01) higher when compared to Volleyball and Handball athletes. Judo athletes presented isometric agonist/antagonist ratio of right limb significantly (p<0.03) lower than the Volleyball and Handball groups, as well as significantly (p<0.01) lower than the Volleyball group in relation to the left limb. The electromechanical delay time presented differences between the groups only in the external shoulder rotation, which the Volleyball group presented significantly lower values of right limb (p<0.01) when compared to the Handball group and left limb times significantly (p<0.01) shorter when compared with the Handball and Judo groups Dynamic peak torque presented difference only for internal shoulder rotation of the right limb, which the Judo group presented values significantly (p<0.001) higher when compared to the Volleyball group. For the left upper limb, a significant difference (p<0.01) was detected in the peak torque angle of internal shoulder rotation between the Judo and Handball groups. The results of the study allow to considering that the practice of each evaluated sports modalities adapts the shoulder of its athletes in different ways. Judo athletes need to perform external shoulder rotation muscular strengthening, both in concentric and eccentric modes due to muscle imbalance caused by the specificity of the modality. Volleyball athletes have reasonable muscle balance in the shoulder joint due to the high levels of eccentric strength of external rotation, in addition the short time periods of electromechanical delay presented by these athletes reinforce even more the balance of this joint. Handball athletes have reasonable muscle balance in the shoulder joint; however, they presented high values of electromechanical delay, so it is indicated that these athletes need to perform muscular strengthening of external rotation of the shoulder in order to reduce the time required to activate these muscles.

O objetivo deste estudo foi avaliar e comparar o equilíbrio de força muscular e o tempo de retardo eletromecânico na articulação do ombro entre atletas de diferentes modalidades esportivas, os quais utilizam predominantemente rotações internas e externas de ombro durante as suas práticas esportivas. Fizeram parte do estudo 41 sujeitos do sexo masculino, sendo 15 atletas profissionais de Voleibol (24,07 ± 5,13 anos; 91,60 ± 11,67 kg; 198,47 ± 5,90 cm), 14 atletas profissionais de Judô (26,64 ± 7,30 anos; 87,36 ± 15,20 kg; 178,07 ± 6,90 cm) e 12 atletas universitários de Handebol (23,17 ± 4,70 anos; 84,75 ± 13,50 kg; 182,08 ± 6,20 cm). Para a mensuração de força máxima, de diferença contralateral (i.e. lados direito vs. esquerdo) e para o cálculo das razões entre rotação interna e externa de ombro, os participantes realizaram testes de dinamometria isocinética em condições isométricas e isocinéticas. Durante os testes isométricos foi realizada a coleta do sinal eletromiográfico dos músculos peitoral maior e infraespinal, o que possibilitou o cálculo do retardo eletromecânico. Os resultados demonstram que atletas de Judô possuem força isométrica de rotação interna de ombro significativamente (p<0,01) maior quando comparados com atletas de Voleibol e de Handebol. Atletas de Judô apresentam valores de razão agonista/antagonista isométrica de membro direito significativamente (p<0,03) inferiores aos grupos Voleibol e Handebol, bem como significativamente (p<0,01) inferiores ao grupo Voleibol em relação ao membro esquerdo O tempo de retardo eletromecânico apresentou diferenças entre os grupos somente na rotação externa, em que o grupo Voleibol apresentou valores do membro direito significativamente (p<0,01) mais curtos quando comparados com o grupo Handebol e valores de membro esquerdo significativamente (p<0,01) mais curtos quando comparados com os grupos Handebol e Judô. Picos de torque isocinéticos apresentaram diferença somente para rotação interna de membro direito, em que o grupo Judô apresentou valores significativamente (p<0,001) maiores quando comparados com o grupo Voleibol. Já para membro esquerdo, detectou-se diferença significativa (p<0,01) no ângulo de pico de torque de rotação interna de membro esquerdo entre o grupo Judô e Handebol. Os resultados do estudo permitem concluir que a prática de cada modalidade esportiva avaliada neste estudo promoveu adaptação dos músculos do ombro, de acordo com a demanda da modalidade esportiva. Assim, atletas de Judô necessitam realizar reforço dos músculos rotadores externos do ombro, tanto concêntrica quanto excentricamente, visto o desequilíbrio muscular causado pela especificidade da modalidade. Por outro lado, atletas de Voleibol apresentam satisfatório equilíbrio muscular na articulação do ombro por conta de altos níveis de força excêntrica de rotação externa exigidos na prática deste esporte; além disso, os curtos períodos de tempo de retardo eletromecânico apresentados por estes atletas reforçam a constatação de equilíbrio desta articulação. Atletas de Handebol apresentam satisfatório equilíbrio muscular na articulação do ombro, entretanto apresentam valores altos de retardo eletromecânico, sendo indicado que estes atletas realizem reforço de rotação externa de ombro, sobretudo em velocidade elevada, com o objetivo de diminuir o tempo necessário para ativar estes grupos musculares. / The purpose of this study was to evaluate and compare the muscular balance and the electromechanical delay time of the shoulder joint between athletes of different sports modalities who use predominantly internal and external rotations of the shoulder. The study consisted of a total of 41 male subjects, of whom 15 were professional Volleyball players (n = 15, 24.07 ± 5.13 years, 91.60 ± 11.67 kg, 198.47 ± 5.90 cm), 14 professional Judo athletes (26.64 ± 7.30 years, 87.36 ± 15.20 kg, 178.07 ± 6.90 cm) and 12 university Handball athletes (23.17 ± 4.70 years, 84.75 ± 13.50 kg, 182.08 ± 6.20 cm). To evaluate peak torque, upper limb side-to-side asymmetry and for the calculation of conventional and functional ratios, all subjects performed isokinetic dynamometry tests under isometric and dynamic conditions. During the isomeric tests, the electromyographic signal was collected from the pectoralis major and infraspinal muscles, which allowed the calculation of the electromechanical delay. The results demonstrate that Judo athletes have internal shoulder rotation isometric strength significantly (p<0.01) higher when compared to Volleyball and Handball athletes. Judo athletes presented isometric agonist/antagonist ratio of right limb significantly (p<0.03) lower than the Volleyball and Handball groups, as well as significantly (p<0.01) lower than the Volleyball group in relation to the left limb. The electromechanical delay time presented differences between the groups only in the external shoulder rotation, which the Volleyball group presented significantly lower values of right limb (p<0.01) when compared to the Handball group and left limb times significantly (p<0.01) shorter when compared with the Handball and Judo groups Dynamic peak torque presented difference only for internal shoulder rotation of the right limb, which the Judo group presented values significantly (p<0.001) higher when compared to the Volleyball group. For the left upper limb, a significant difference (p<0.01) was detected in the peak torque angle of internal shoulder rotation between the Judo and Handball groups. The results of the study allow to considering that the practice of each evaluated sports modalities adapts the shoulder of its athletes in different ways. Judo athletes need to perform external shoulder rotation muscular strengthening, both in concentric and eccentric modes due to muscle imbalance caused by the specificity of the modality. Volleyball athletes have reasonable muscle balance in the shoulder joint due to the high levels of eccentric strength of external rotation, in addition the short time periods of electromechanical delay presented by these athletes reinforce even more the balance of this joint. Handball athletes have reasonable muscle balance in the shoulder joint; however, they presented high values of electromechanical delay, so it is indicated that these athletes need to perform muscular strengthening of external rotation of the shoulder in order to reduce the time required to activate these muscles.

Despite years of research, females continue to have a higher incidence of non-contact ACL injuries. One of the major findings of this research is that males and females perform certain tasks, such as, cutting, landing, and single-leg squatting, differently. In particular, females tend to move the knee into a more valgus position; a motion putting the ACL at risk for injury. Yet the underlying spinal control mechanisms modulating this motion are unknown. Additionally, the mechanisms regulating the ability to rapidly initiate and produce maximal torque are also unknown. Therefore, the purpose was to: 1) determine if the sexes modulate spinal control differently, 2) examine the contributions of spinal control mechanisms to valgus knee motion, and 3) identify contributions of spinal control to the ability to rapidly produce force. The spinal control variables were the first derivative of the Hoffmann (H)-reflex, the first derivative of extrinsic pre-synaptic inhibition (EPI), the first derivative of intrinsic pre-synaptic inhibition (IPI), recurrent inhibition (RI), and V-waves. To assess the neuromuscular system’s ability to rapidly activate, rate of torque development (RTD) and electromechanical delay (EMD) were measured. Lastly, valgus motion was determined by the frontal plane projection angle (FPPA). The results reveal males and females do modulate spinal control differently; specifically males had an increased RTD, which is the slope of the torque-time curve, and increased RI, which is a post-synaptic regulator of torque output. However, the spinal control mechanisms did not significantly contribute to FPPA at the knee. EMD which is the time lag from muscle activity to torque production was significantly predicted by the spinal control mechanisms. Specifically, EPI, a modulator of afferent inflow from peripheral and descending sources, IPI, a regulator of Ia afferent inflow, and sex significantly contributed to EMD. Lastly, the spinal control mechanisms significantly contributed to RTD. Specifically, IPI, sex, and V-waves, a measure of supraspinal drive, all significantly contributed to RTD. / Graduation date: 2009

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