Why doesn't my sprinter's knee come up in recovery?
A trailing recovery leg is a longer lever that takes longer to swing through, and the cause is rarely the knee itself.
A coach watching from the infield sees it before anything else. After the foot leaves the ground, the leg is meant to fold and swing through fast, close to the body. Instead it trails out behind, long and low, and only folds late, if at all.
Why a long lever is expensive
A folded leg is a short lever, and a short lever swings through fast for very little effort, the same reason a bent arm swings faster than a straight one. A leg that stays extended behind the athlete has to travel further to get back under the hips for the next strike, and that costs either time or a rushed, low recovery that never gets the knee properly forward. Either way, the athlete is working harder to produce the same stride rate.
What usually causes it
- Weak hip flexors. The muscle group that actually pulls the thigh forward has nothing behind it, so the shin drags rather than folds.
- A cadence too low for the effort being put in. At a higher stride rate the leg has less time on the ground and more incentive to fold quickly; a laboured stride gives it no reason to.
- Fatigue. A fresh sprinter's knee folds cleanly and a tired one's does not, which is why the same rep filmed at the start and the end of a session can look like two different athletes.
- Reaching for a longer stride. An athlete trying to cover more ground by throwing the foot forward, rather than pushing harder behind the body, drags the leg out to do it, the same fault that causes overstriding at the front end of the stride.
What the Film Room measures, and what it does not hand you
Knee fold and extension is one of the six measures the sprint setting reports, alongside trunk lean, elbow angle, overstride and ground contact time. It gives you a number to track week to week rather than trying to judge a blur by eye. Worth being straight about the rest of it: unlike overstride or elbow angle, knee fold does not currently have a drill attached to it in the app's own list. That is not an oversight so much as the same honesty the throws event applies to the arm and the trunk: a number only earns a named drill once the app can reliably call it a fault, and it does not yet for this one. The standard remedies, fast-leg cycling drills and A-skips done for height rather than distance, are still the right answer. They are just yours to name, not the app's.
A side-on camera reads the fold in the plane facing it and nothing else. It cannot see the knee swinging out to the side, which is a hip fault wearing a knee costume, and it cannot tell you whether a low recovery on the last rep of a session is weakness or simply fatigue. Both need a second look, not just a second clip.
Time your next meet with the phones you already have
Timing, the Film Room and the speed gates are free forever. Publishing results to your own page starts at $59 a month.
Related
How far forward should a sprinter lean?
A lot out of the blocks, very little at top speed, and never by bending at the waist, which is the version that gets taught by accident.
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