Hamstring injuries are the most common noncontact injury in elite sport. Despite increased research efforts, these injury rates continue to rise. Recent evidence has shown that short muscle fiber lengths can increase the risk of hamstring injury in elite soccer players. This study aimed to see how fascicle lengths change following training interventions of either lengthening or shortening contractions.
Twenty-eight healthy males trained three times per week for six weeks, followed by a reassessment after four weeks off. Those who trained with lengthening contractions saw a rapid (<14 days) increase in fascicle length, with a loss of any gains following the four weeks off at the end. Those who trained with shortening contractions saw a rapid (<14 days) reduction in fascicle length, with no changes following the four week break.
These findings have implications for injury prevention and rehabilitation practices which should consider the contraction mode and the effect of de-training. An example from elite soccer is prescription of a lengthening training intervention (e.g. Nordic Hamstring Exercise) to an athlete.
This works great, unless the athlete stops doing the exercises in-season or goes on holiday at the end of the season.
Then, all of the hard work is for nothing, with significant reductions in muscle fiber length and potential increases in injury risk.
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