Why is my sprinter's ground contact time longer on one side?
It might be a real limp worth checking. It might also be a question the Film Room cannot currently answer, because the number it reports is not split left from right.
A coach watches the ground contact number in the Film Room bounce around between runs and starts to wonder whether one leg is spending more time on the ground than the other. It is a fair question to ask about an athlete's stride. It is not a question the current number can answer.
What the number actually is
Ground contact time on a running clip comes from tracking both ankles across the video and finding the stretches where each one sits near the lowest point it reaches in the clip. Every contact from both feet, left and right, gets pooled into one list, sorted by time, and averaged together into the single figure that shows up in the report. It is one number across every strike the camera caught. It was never built to separate left from right, so right now, it cannot.
So what can you actually check
- Slow the clip down and count by eye: does one foot's contact visibly last longer than the other's, strike after strike?
- Look for a limp or a shortened stride on one side before the numbers, since a real compensation pattern usually shows up in stride length or a lean well before contact time would prove anything.
- Treat a suspected medical issue as a question for training or medical staff, not for a phone's video analysis.
If there genuinely is a real asymmetry, it deserves attention, and film is still useful for showing a coach or a trainer what to look at. It just is not the tool that will hand you the left-versus-right comparison on its own.
A single side-on camera makes this harder than the software alone does. During large parts of the stride the far leg is partly hidden behind the athlete's own body, so its ankle track carries less confident data than the near leg's the whole time. Even a future version that split contact time by foot would be reading its weakest data from exactly the side you most want to trust.
Time your next meet with the phones you already have
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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.
Read →Why does your sprinter's foot turn out when they run?
A side-on camera cannot see which way a foot points, and from where most coaches film, neither can you.
Read →Why does your high jumper's plant foot never land in the same spot?
A side-on camera reads the vertical arc of a jump well and has no idea where the plant foot actually landed on the ground, which is usually the real question.
Read →Try it: Sprint timer app: 40-yard dash and flying sprints with one phone