Are your hamstrings sprint ready?
As we guide an individual through rehab following a hamstring strain, we must ask if they have the ability to create the force needed to produce movements needed for the terminal task. The individual may have excellent coordination under low magnitudes or rates of force but unable to express them at intensities needed to perform.
For hamstring rehab, this is often seen in the ability to execute a sprint at 75% of top speed only to have their form break down or symptoms to re-appear at 80%. The threshold or tolerance for force production has not yet been restored. The important piece to respect here is that force expression must be specific to the magnitudes and rates needed for the terminal task.
A 2014 study by Sun et al clearly revealed the gap between isometric strength testing and the forces sustain in sprinting. These data showed that knee flexor force during the initial stance phase and late swing phase were 40% and 50% larger respectively than that produced by isometric knee flexion. These forces reached up to 10 times the subject’s body weight! With this in mind, we must be able to see how a prone hamstring manual muscle test is a great checkpoint but tells us very little about their ability to sprint at terminal intensities.
To assure your hamstrings are sprint ready, make sure you are respecting and testing the full extent of the forces involved in the task!
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Credit: Sun Y, Wei S, Zhong Y, Fu W, Li L, Liu Y. How joint torques affect hamstring injury risk in sprinting swing–stance transition. Medicine & Science in Sports & Exercise. 2015;47(2):373-380.