Efeitos do treino excêntrico versus concêntrico na força máxima e EMG dos extensores e flexores da perna
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2011
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A presente dissertação teve como propósito comparar o efeito do treino concêntrico e excêntrico no desenvolvimento da força máxima dos quadricípedes e isquiotibiais. Neste sentido, e antes de aplicarmos o programa de treino, era importante analisar a fiabilidade dos equipamentos que iríamos utilizar na avaliação e treino da força.
O estudo 1 mostrou que existe uma alta reprodutividade da força máxima concêntrica, isométrica e excêntrica dos extensores e flexores da perna quando avaliados no dinamómetro isocinético REV 9000 (Technogym), o que nos permite confirmar que este equipamento pode ser utilizado, com segurança, em estudos científicos e em programas de reabilitação ou desenvolvimento da força muscular.
No estudo 2, também pretendíamos avaliar a fiabilidade mas agora do registo electromiográfico, concluímos que temos de ter alguma precaução na sua utilização, porque sem remover os eléctrodos a fiabilidade é considerada alta, contudo, retirando os eléctrodos a reprodutividade dos seus resultados torna-se mais baixa, provavelmente devido à nova posição dos mesmos. De todos os músculos analisados o Rectus Femoris (RF) parece ser aquele que apresenta uma menor fiabilidade.
No estudo 3 comparamos o efeito do treino isocinético excêntrico vs concêntrico e concluímos que os ganhos do treino excêntrico foram superiores e mais específicos do que os ganhos do treino concêntrico, assim como os valores de destreino (diminuição da força máxima dinâmica e isométrica), também superiores no grupo excêntrico. No entanto, as quebras registadas na fase de destreino foram inferiores aos ganhos obtidos durante o treino.
A questão das adaptações neurais terá sido um dos factores que contribuíram para o aumento da força máxima isométrica e dinâmica do treino isocinético concêntrico e excêntrico, no entanto, estas adaptações parecem ser maiores no treino excêntrico, o que poderá estar relacionado com a maior intensidade desenvolvida durante estas acções. Esta foi uma das conclusões do estudo 4. em que o grupo que realizou o treino excêntrico conseguiu ganhos de força e de energia na amplitude do sinal eléctrico superiores ao grupo concêntrico.
Concluímos, através dos resultados do estudo 5, que existe uma correlação baixa a moderada entre a força máxima isométrica e dinâmica avaliada através do dinamómetro isocinético e a força máxima de reacção no solo / tempo de voo nos diferentes testes de impulsão vertical. O estudo mostra que a avaliação da força máxima realizada nos membros inferiores é independente dos diferentes exercícios e protocolos de avaliação. Julgamos ser necessário mais investigações para determinar protocolos de avaliação que estejam de acordo com a tarefa, específicos, em cadeia aberta ou fechada, e acessíveis para que possamos ter informação mais útil e válida para os treinadores e preparadores físicos.
Na generalidade, os resultados destes estudos sugerem que o treino excêntrico permite, para o mesmo período de tempo de treino, obter ganhos superiores em relação ao treino concêntrico. Todavia, julgamos ser importante preparar o atleta para um treino mais intenso, como é o caso do treino excêntrico, ou avaliar os atletas antes da aplicação do programa de treino para saber se têm capacidade para realizar este tipo de treino de desenvolvimento da força muscular, de forma segura, sem correr qualquer risco de lesão.
The purpose of this study was to compare the effect of concentric and eccentric training in developing maximal strength of quadriceps and hamstrings. In this sense, and before applying the training program, it was important to examine whether the protocols for evaluating the strength or the reliability of equipment we would use. So from the five studies that we did, the first two were devoted to this issue. The first empirical study showed a high reproducibility in concentric, isometric and eccentric peak torque for knee extensor and flexors muscles indicating that the REV9000 (Technogym) isokinetic dynamometer can be used in rehabilitation, sports medicine and for future sports performance studies. This study also showed that dynamic control ratio (Hecc:Qconc) can be a more valid indicator for imbalance reciprocal parameters. In the second study we also wanted to assess the reliability, but now of surface electromyography of the average full wave rectified signal (AvgEMG) and peak torque (PT) of quadriceps. The results of this study showed a high reproducibility of eccentric, concentric and isometric isokinetic strength for knee extensor muscles assessed with the REV9000 showing that this isokinetic device can be used for legitimate research or patient evaluation. With respect of EMG parameters we have to be more carefull, because if we don`t remove the electrodes the ICC is high, but if we remove them then reproducibility becames lower, probably due to factors affecting new electrode placement. Furthermore, the RF muscle seems to be less reliable that VL and VM muscles. In the third study the purposes were to examine the effect of 8 - week concentric versus eccentric isokinetic training program on the isometric and dynamic strength of the knee extensors and flexors. Additionally, the experimental program was followed by a 4-week detraining period that was also inspected. In conclusion, this study showed that strength gains after eccentric training were greater and more specific comparing with concentric training. In addition, the isokinetic strength bilateral ratios increased more in eccentric than concentric group and Hconc:Qconc ratio did not suffer significant changes. Greater declines in muscle strength were observed in eccentric training but still retained at a higher level than concentric training probably due to the higher gains achieved during the training period. Neural adaptations have been one of the factors that contributed to the increase of isometric and dynamic peak torque after isokinetic concentric and eccentric training. However, these neural adaptations seem to be higher in the eccentric training, which may be related to higher intensity developed during eccentric actions. This was the purpose of fourth study, to examine the effect of 8 - week concentric versus eccentric isokinetic training program on the electromyogram signal amplitude (EMG) and isometric and dynamic maximum strength on the knee extensors. In conclusion, this study showed that concentric training improve peak torque and electrical activation in all kind of contractions (concentric, isometric and eccentric), but just with statistically significant differences in peak torque and Vastus Medialis of isometric contraction. The eccentric training also improve the electrical activation in all muscles with statistically significant differences on Vastus Lateralis in all contractions and Vastus Medialis in concentric contraction, regarding to peak torque also improve in all contractions with statistically significant differences in eccentric contraction. Available research is contradictory when explaining the relationship between isokinetic knee tests and vertical jump tests. The aim of fifth study was to to identify relations among various bilateral closed kinetic chain tests and traditional isokinetic dynamometry tests. A low to moderate correlation between isokinetic strength and vertical jump tests was found supporting the view that in maximal efforts, the maximal power potential of lower limbs may be independent from the kind of exercise or tests. Further research needs to be conducted to determine a simple yet valid test to evaluate maximal power according to specific task (open or closed kinetic chain) usefull for strength and conditioning specialist to analyse the performance or for clinicians to analyse possible asymmetries. Overall, the results of these studies suggest that eccentric training achieve, for the same period of training, higher gains compared to concentric training. However, we believe it is important to prepare the athlete for a more intense workout, such as eccentric training or assess the athletes before the implementation of the training program to see if they have the capacity to perform this type of training to develop muscular strength, safely without any risk of injury.
The purpose of this study was to compare the effect of concentric and eccentric training in developing maximal strength of quadriceps and hamstrings. In this sense, and before applying the training program, it was important to examine whether the protocols for evaluating the strength or the reliability of equipment we would use. So from the five studies that we did, the first two were devoted to this issue. The first empirical study showed a high reproducibility in concentric, isometric and eccentric peak torque for knee extensor and flexors muscles indicating that the REV9000 (Technogym) isokinetic dynamometer can be used in rehabilitation, sports medicine and for future sports performance studies. This study also showed that dynamic control ratio (Hecc:Qconc) can be a more valid indicator for imbalance reciprocal parameters. In the second study we also wanted to assess the reliability, but now of surface electromyography of the average full wave rectified signal (AvgEMG) and peak torque (PT) of quadriceps. The results of this study showed a high reproducibility of eccentric, concentric and isometric isokinetic strength for knee extensor muscles assessed with the REV9000 showing that this isokinetic device can be used for legitimate research or patient evaluation. With respect of EMG parameters we have to be more carefull, because if we don`t remove the electrodes the ICC is high, but if we remove them then reproducibility becames lower, probably due to factors affecting new electrode placement. Furthermore, the RF muscle seems to be less reliable that VL and VM muscles. In the third study the purposes were to examine the effect of 8 - week concentric versus eccentric isokinetic training program on the isometric and dynamic strength of the knee extensors and flexors. Additionally, the experimental program was followed by a 4-week detraining period that was also inspected. In conclusion, this study showed that strength gains after eccentric training were greater and more specific comparing with concentric training. In addition, the isokinetic strength bilateral ratios increased more in eccentric than concentric group and Hconc:Qconc ratio did not suffer significant changes. Greater declines in muscle strength were observed in eccentric training but still retained at a higher level than concentric training probably due to the higher gains achieved during the training period. Neural adaptations have been one of the factors that contributed to the increase of isometric and dynamic peak torque after isokinetic concentric and eccentric training. However, these neural adaptations seem to be higher in the eccentric training, which may be related to higher intensity developed during eccentric actions. This was the purpose of fourth study, to examine the effect of 8 - week concentric versus eccentric isokinetic training program on the electromyogram signal amplitude (EMG) and isometric and dynamic maximum strength on the knee extensors. In conclusion, this study showed that concentric training improve peak torque and electrical activation in all kind of contractions (concentric, isometric and eccentric), but just with statistically significant differences in peak torque and Vastus Medialis of isometric contraction. The eccentric training also improve the electrical activation in all muscles with statistically significant differences on Vastus Lateralis in all contractions and Vastus Medialis in concentric contraction, regarding to peak torque also improve in all contractions with statistically significant differences in eccentric contraction. Available research is contradictory when explaining the relationship between isokinetic knee tests and vertical jump tests. The aim of fifth study was to to identify relations among various bilateral closed kinetic chain tests and traditional isokinetic dynamometry tests. A low to moderate correlation between isokinetic strength and vertical jump tests was found supporting the view that in maximal efforts, the maximal power potential of lower limbs may be independent from the kind of exercise or tests. Further research needs to be conducted to determine a simple yet valid test to evaluate maximal power according to specific task (open or closed kinetic chain) usefull for strength and conditioning specialist to analyse the performance or for clinicians to analyse possible asymmetries. Overall, the results of these studies suggest that eccentric training achieve, for the same period of training, higher gains compared to concentric training. However, we believe it is important to prepare the athlete for a more intense workout, such as eccentric training or assess the athletes before the implementation of the training program to see if they have the capacity to perform this type of training to develop muscular strength, safely without any risk of injury.
Descrição
Tese de Doutoramento em Ciências do Desporto e Educação Física, especialidade Ciências do Desporto
Palavras-chave
Força , Treino , Treino isocinético , Electromiografia , Fiabilidade , Quadricípedes , Isquiotibiais , Diferenças bilaterais , Rácio antagonista , Agonista , Saltos impulsão vertical