Why We Can’t Predict a Hamstring Strain.
Every preseason, somewhere, a physio or S&C coach lines a squad up in front of a dynamometer, tests hamstring strength, ranks the results, and flags the weakest few as “high risk.” It feels rigorous. It feels like exactly the kind of thing screening should look like. And the uncomfortable truth, backed by some fairly large studies now, is that it doesn’t actually work.
The most convincing of these followed 367 professional footballers across more than 500 player-seasons, measuring how quickly they could generate torque in their hamstrings during standard preseason testing. Over that time there were 65 hamstring strains. When the researchers went back and compared the injured players’ preseason numbers to everyone else’s, there was essentially nothing there — no meaningful difference in how fast they produced force, no meaningful difference in muscle activation timing. The same story turns up again when you look at simple eccentric strength testing, or the classic hamstring to quadriceps ratio that’s been a screening staple for decades. None of them reliably separate the athletes who go on to strain a hamstring from the ones who don’t.
This tends to land awkwardly, because we know these same measures are genuinely useful in other contexts. Rate of force development is a legitimately good tool for tracking whether a previously injured hamstring has actually recovered its explosive capacity, and it’s sensitive enough to pick up fatigue after a hard match or a heavy sprint session. It’s just not a crystal ball. A test can be a perfectly good measure of where an athlete currently sits, without being any good at forecasting where they’re headed.
What does seem to carry more signal is something more dynamic: how an athlete is actually producing force during sprinting itself, particularly the horizontal component of that force, tracked across a season rather than measured once in preseason and filed away. Drops in that capacity through the season have shown a closer relationship to strain risk in the weeks that follow. It makes intuitive sense when you think about it — a single test in November tells you very little about the accumulated fatigue, the change in training load, or the technical breakdown that’s building in an athlete’s sprint mechanics come June.
The other consistent finding across this research is a fairly humbling one: the strongest predictors of a future hamstring strain remain the boring, non-modifiable ones — being older, and having strained it before. That’s not a satisfying answer for anyone wanting a slick screening protocol, but it’s an honest one.
None of this means we should throw out strength and RFD testing. It means we should be honest about what it’s for. It’s a rehabilitation tool, a return to play tool, and a fatigue monitoring tool. It is not, on its own, a crystal ball for who gets injured next. The moment we start using it as one, we risk giving athletes and coaches false reassurance on the ones who test well, and unnecessary alarm over the ones who don’t.
