published_or_final_version / Sports Science / Master / Master of Science in Sports Science

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Running is achieved by cyclic execution of movements that ultimately allows a person to move. Each cycle is divided into two phases. The first phase is where power is absorbed as the body\'s center of mass is lowered and decelerated. The second being where power is generated and the center of mass is propelled upwards and forwards. Power absorption is primarily done by quadriceps muscles while plantar flexors generate most of the power during push-off phase. Variations in speed and slope are met by adjustments in the same direction of force produced by lower limb muscles and, due to changes in energy expenditure, of heart rate. In this context, analysis of variability offer a non-invasive way to measure how well-adjusted muscles are to cope with variations in demand. Thus, our aim was to investigate the relationship between the variability of contractions of muscles from the quadriceps and plantar flexors with changes in speed and slope and in heart rate. Secondarily, we sought to verify if the patterns observed in a restricted group of subjects could also be noted in a wider population. To answer these questions, we used electromyography to collect data of intervals between successive contractions of vasti and gastrocnemius muscles of seventeen runners across several target runs. These runs were chosen with several different speeds and slopes. Runners were divided into two experimental groups: Experiment 1 contained no restrictions regarding age and fitness level while Experiment 2 did control for these variables. Linear regressions and gradients showed that even though variability estimators correlated negatively to speed and/or slope, they could be better explained by changes in heart rate. Thus our main conclusion was that variability between contractions is inversely proportional to muscle activation, in relation to its maximum capacity. As a consequence, different combinations of speed and slope could result in the same variability despite differences in metabolic profile, as long as the power output remains constant. Due to methodological issues, we could not reach a decisive conclusion regarding the comparison between the more restricted and more heterogeneous groups of volunteers, although results suggest that the runners respond to changes of speed and slope in a similar way regardless of differences in age and fitness level / Durante a corrida, uma série de movimentos é realizada de forma cíclica que, em última análise, fazem com que o corpo se desloque. Cada ciclo é dividido em uma fase em que ocorre absorção de trabalho conforme o centro de massa é rebaixado e desacelerado e uma fase em que ocorre produção de trabalho, conforme o centro de massa é impulsionado para cima e para frente. Os músculos do quadríceps e flexores plantares são os principais responsáveis pela absorção e geração de trabalho, respectivamente. Variações na velocidade da corrida e na inclinação do terreno requerem ajustes da força muscular e, como consequência, da freqüência cardíaca. Neste contexto, análises de variabilidade oferecem uma maneira de medir a adequação do sistema muscular às variações na demanda. Assim, buscamos investigar a relação entre a variabilidade das contrações de músculos do quadríceps e flexores plantares com alterações na velocidade, inclinação e potência; bem como verificar se os padrões observados em um grupo restrito de indivíduos se aplicavam a uma amostra mais variada. Para isso, coletamos dados de intervalos entre contrações do vasto e gastrocnêmio de dezessete voluntários durante corridas realizadas em diferentes combinações de velocidade e inclinação da esteira. Os sujeitos foram divididos em dois grupos experimentais: no Experimento 1, não houve restrições quanto à idade e condicionamento, enquanto que no Experimento 2 essas variáveis foram controladas. Regressões lineares e gradientes mostraram que, embora os estimadores de variabilidade correlacionem negativamente com velocidade e inclinação, eles são melhor explicados por mudanças no consumo energético (i.e.,frequência cardíaca). Assim, concluímos que a variabilidade é inversamente proporcional à força muscular, em relação à sua capacidade máxima. Como conseqüência, diferentes combinações de velocidade e inclinação podem resultar na mesma variabilidade, apesar das diferenças no perfil metabólico. Devido a complicações metodológicas, não pudemos chegar a uma conclusão definitiva em relação a comparação entre voluntários dos Experimentos 1 e 2, embora os resultados sugiram que corredores respondam a mudanças de velocidade e inclinação de maneira semelhante, independentemente de diferenças de idade e nível de condicionamento

Introduction: Rugby is a professional sport which places emphasises on strength, power, speed and endurance. Therefore the accurate assessment of rugby performance is very important for sports and exercise therapists to enable peak performance for the players. Lower limb strength is often tested by means of isokinetic testing, whilst functional power is tested by means of the vertical jump test. Sophisticated equipment used in the measurement of performance indicators, are often not available in smaller communities and rural areas. A good correlation between laboratory testing and functional testing could be of great value for determining performance in less fortunate communities. Aim of Study: To determine the relationship between isokinetic strength testing of the quadriceps and hamstring muscle groups and vertical jump performance in rugby players. Methods: Fifty one male, rugby players who were part of the Varsity Cup Tournament in (2011) participated in this study. Ethical approval was given by the Human Research Ethics Committee (HREC) of the University of Witwatersrand. Height and weight were measured. Isokinetic knee extensor and flexor strength was tested (Biodex system 4 dynamometer TM ) at 60˚/sec (5 repetitions), 180˚/sec (10 repetitions) and 300˚/sec (15 repetitions). A single leg vertical jump was done using the Vertec and the performance was assessed as maximal height jump in centimetres. Descriptive statistics (mean and standard deviation) are reported for all outcomes. The SPSS software (IBM. SPSS version 21) was used for analysis. A Pearson's Product Moment Correlation coefficient was calculated between the isokinetic parameters of quadriceps and hamstring muscles and the vertical jump height and power (watts). An independent t-test and a paired t-test were used to calculate the differences between the forward and backline players and the dominant (Dom) and non-dominant (ND) legs. Results: The mean age of the participants was 21.4 ± 1.2 years; they were 1.83 ± 7.4m tall and weighed 99.3 ± 13.8kg. There were 26 forward players (mean height of 1.88 ± 7.2m and mean weight of 109.9 ± 10.3kg) and 25 backline players (mean height of 1.80 ± 5.5m and mean weight of 88.3 ± 6.1kg). The forwards were significantly taller and heavier than the backline players (p = 0.0001). The forwards produced significant greater peak power in the vertical jump than the backline players in both the dominant and non-dominant legs (p=0.0001). The PT (Nm) decreased as the angular velocity increased from 60˚/sec to 300˚/sec. A significant negative correlation (r = - 0.313; p = 0.025) between peak torque (PT) concentric strength from the hamstrings at 60º/sec and the vertical jump height on the non-dominant side were found. Quadriceps PT to vertical power at the higher velocities showed significant correlations at 180º/sec (dominant: r = 0.294; p = 0.011) and 300º/sec (dominant: r = 0.352; p = 0.011; non-dominant: r = 0.293; p = 0.037). No significant correlations were found between peak torque and vertical jump height when corrected for body weight. When correlating PT and vertical jump power corrected for body weight significant negative correlations was found at 180º/sec (dominant: r = 0.319; p = 0.022; non-dominant: r = 0.305; p = 0.030) for the hamstrings. Conclusion: The findings from the presented study found no significant correlation between lower limb isokinetic knee muscle torque parameters and vertical jump performance in rugby union players. Future research should investigate the relationship between isokinetic testing and vertical jump height by including the parameters of a multi joint mechanism.

Resistance training is widely prescribed for rehabilitation of injuries and as a method to improve athletic performance. It is accepted that resistance training increases the maximal force production of whole muscle and it has been suggested that the velocity of shortening can increase as well. However, little is known about the effects of resistance training at the cellular level. Therefore, we investigated morphology, force production, velocity, and force-velocity-power relationships of single chemically skinned muscle fibers from chronically resistance trained humans, including cross sectional area (CSA), peak Ca²⁺ -activated force production (P₀), specific tension (P₀/CSA), unloaded shortening velocity (V₀), and isotonic contractions. The untrained group (NT) group consisted of sedentary males (n=6, age =27 ± 2 yrs) while the chronically trained group (CHRT) group consisted of males with 7.7 ± 0.4 yrs resistance training experience (n=6, 22 ± 1 yrs). Maximum voluntary isometric and isokinetic knee extensor strength were measured along with 6 repetition maximum (6RM) free weight bench press and leg press. Muscle biopsies were obtained from the vastus lateralis. Chemically skinned single muscle fibers were mounted between a force transducer and servo-controlled motor and subjected to slack tests to determine peak Ca²⁺ -activated force (P₀) and unloaded shortening velocity (V₀). Isotonic load clamps were used to determine the force-velocity-power relationship. All fiber experiments were performed at 15°C. Fiber myosin heavy chain (MHC) content was determined by gel electrophoresis. The CHRT group was 119% and 81% stronger for 6RM leg press and bench press respectively. Peak isometric torque was 28% greater for the CHRT subjects and was significantly higher at all isokinetic speeds tested. No differences were seen in strength or isokinetic power between groups after normalization for lean body mass. CHRT fibers (n=213) expressing type I, IIa, and I₀a/IIx MHC were significantly greater in CSA (+41%, +51%, and +33%, respectively) and produced significantly greater P₀ (+37%, +48%, and +34%, respectively) than NT fibers (n=236). However, P₀/CSA was not different between CHRT and NT groups. Fibers expressing type IIa/IIx fibers produced greater P₀/CSA than IIa which produced greater P₀/CSA than type I. The P₀/CSA relationship between fibers within groups was type IIa/IIx>IIa>I and was significant for both groups. Fiber V₀ was not different between groups. Absolute power was significantly greater in the CHRT for all fiber types whereas power normalized for fiber volume was not different between groups. This resulted in a significantly greater force at peak power for all but type IIa/IIx fibers and trends for greater velocity at peak power. Single-cell contractile function in terms of V₀ and P₀/CSA, measured under standardized conditions, appears to be unaltered as a result of long term CHRT in young adult males. Group differences in absolute P₀ can be attributed solely to the greater CSA of the CHRT fibers. Long-term CHRT is not associated with a difference in fiber V₀. Therefore, the greater power was due entirely to the greater force. These data suggest that differences in whole muscle strength and power between NT and CHRT groups are primarily due to differences in fiber CSA rather than differences in cross-bridge mechanisms of contraction. Supported by National Institute of Health grant R3AR46392A. / Graduation date: 2002

Graduation date: 2003

Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisor: Stuart A. Binder-Macleod, Dept. of Physical Therapy. Includes bibliographical references.

Thesis (M.S.)--University of Delaware, 2006. / Principal faculty advisor: Stuart A. Binder-Macleod, Dept. of Physical Therapy. Includes bibliographical references.

Thesis (M.S.)--University of Delaware, 2006. / Principal faculty advisor: Cheng-Shun (Richard) Fang, Dept. of Health, Nutrition, and Exercise Sciences. Includes bibliographical references.

Thesis (M. Med. Sc.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 68-69).