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Blog Tênis na Rede » Potência = velocidade máxima no ponto de contato

Potência = velocidade máxima no ponto de contato 8 de junho de 2009

Após a preparação do golpe (backswing), podemos caracterizar três importantes fases para os golpes no tênis:

A.  Fase de aceleração da raquete
B.  Fase de contato com a bola
C.  Fase de desaceleração da raquete

foto-01-ciencia010

A fase de aceleração (A) parte de uma velocidade zero (V0), e por isso exige intensas contrações dos músculos envolvidos no golpe. É nesta fase que o executante terá a chance de acelerar a raquete até o ponto de contato com a bola (B). Se a preparação for curta, menor será a possibilidade de acelerar a raquete até o ponto de contato. Se a preparação for muito ampla, apesar do executante ter mais chance de acelerar a raquete, a precisão será prejudicada. Portanto, antes de golpear uma bola, é preciso dosar muito bem esta relação potência/precisão.

Entre algumas variáveis que definem a potência imprimida à bola, sem dúvida uma das mais importantes é a velocidade instantânea (Vi) com que as cordas da raquete atingem a bola.

Com estas informações podemos concluir que para imprimirmos bastante potência à bola, o ideal seria acelerarmos o máximo possível a raquete desde o ponto A até o ponto B. Mas não é tão simples assim: estudos científicos mostram que os atletas de elite, em várias modalidades, não atingem seu alvo com a velocidade máxima. Ocorre uma desaceleração pré-impacto, que pode ser explicada como sendo um mecanismo de ajuste, buscando a precisão. Veja nos quadros a seguir as magnitudes destas reduções de velocidade pré-impacto:

  • SAQUE (TÊNIS)
 

Pico de Velocidade

Velocidade no Impacto

Redução

Ponta da Raquete

144 km/h

97 km/h

33%

  • CHUTE (FUTEBOL)
 

Pico de Velocidade

Velocidade no Impacto

Redução

112 km/h

90 km/h

20%

  • SOCO (BOXE)
 

Pico de Velocidade

Velocidade no Impacto

Redução

Mão

41 km/h

34 km/h

17%

A fase de desaceleração da raquete (C) também é muito importante, principalmente quanto à integridade física dos músculos e tendões do membro superior. Durante esta fase, ou seja, após o impacto com a bola, o executante deve desacelerar a raquete rapidamente em uma distância muito curta. Esta desaceleração, que é chamada de contração excêntrica , requer um gasto energético muito grande e se realizada freqüente e bruscamente pode lesionar os grupos musculares envolvidos. Um exemplo clássico deste tipo de lesão é o tennis elbow, muitas vezes causado pela brusca desaceleração do braço durante o golpe de esquerda (backhand ).

One Comments
Saulo agosto 20th, 2012

Muito boa as dicas e, para mim, a desaceleração pré impacto, na hora do ajustar a batida, foi a melhor.
Parabéns

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