When isometric testing is not enough.
Hamstrings…The bane of all sports injuries. Especially when they rec. Health professionals use an array of tests to determine when an athlete is “ready” to return to sport, one being isometric strength testing.
Lee et al. (2018) showed that a history of previous hamstring injury and an imbalance in isometric strength leads to an increased risk of reinjury. Most rehab protocols focus on strength programs to achieve 90% symmetry between sides. Once this is achieved they are believed safe to return.
But are they??
Sport is chaotic and often testing in a clinical environment does not replicate the real test.
How can we do this without risk of aggravating the athlete?
We do it through measuring Eccentric strength at speed
The kPulley2 (Figure 1) is a flywheel device that measures both concentric and eccentric power.
The beauty of the flywheel means that as the athlete pulls harder the eccentric phase will be met with more resistance, however by nature of its apparatus the speed is never constant. This adds a degree of chaos (and variable speed) to the test in a manner that goes beyond isometric testing in other controlled clinical settings.
The example given here is how an isometric test showed NO asymmetry across sides (figure 2). However, “Eccentric strength test at speed” shows an asymmetry of almost 17% in both Peak (296 V 246N) and Average (275 v 228N) Eccentric forces (Figure 3 and 4).
So is this athlete safe to return to full/unrestricted sport?
At this stage, the research has not been done to validate this method to state otherwise, however in my clinical opinion the answer is no. Not as yet.
An example of one of the exercises I use to address this is shown in figure 5.
It will be important to retest this in the next few weeks to try to reduce the symmetry to less than 10% before we clear him to return to full speed straining.
You want your tests to be as safe and valid as possible. But don’t neglect to embrace the chaotic.