Why does my sprinter's stride get longer but their time doesn't improve?
A longer stride on video is not the same thing as a faster stride, and the gap between the two usually shows up in ground contact time, not in the tape measure.
A sprinter's stride looks longer on video than it did last month. The coach is pleased. Then the watch comes out and the time is the same, or worse. The two measurements are not actually the same thing, and the mismatch is common enough that it is worth working through.
Speed is two numbers, not one
How fast somebody runs is stride length multiplied by stride rate, not stride length on its own. A stride that gets longer while the rate it happens at drops by a similar amount buys nothing. The athlete is covering the same ground per second, just doing it in fewer, bigger pieces.
Where the extra length usually comes from
- Reaching the lead foot further forward on landing, which lengthens the stride by moving the touchdown point ahead of the hip rather than by pushing harder off the ground.
- Spending longer in the air between steps instead of covering more distance during the push, which looks like a bigger stride and times like a slower one.
- A longer backswing of the recovery leg that takes more time to cycle through, so each stride costs more time than the extra distance is worth.
What the Film Room can check that the eye can't
The sprint setting reports overstride (how far the foot lands ahead of the hips), ground contact time, flight time and cadence. Set a clip from a month ago next to a clip from this week and the comparison gets specific: if ground contact time has gone up along with the stride, the extra length is probably a longer push. If overstride has gone up instead, the foot is landing further out front and likely braking on contact, which is the kind of longer stride that costs time rather than buying it.
A single 2D camera reads position frame by frame. It does not measure force, so it cannot tell you whether a longer stride is coming from a stronger push, a flexibility issue, or an athlete trying to look like they are reaching further. It can tell you that the stride changed and roughly how. Why it changed is still a conversation with the athlete, not a number.
Time your next meet with the phones you already have
Timing, the Film Room and the speed gates are free forever, with no account. A Club plan, $71 a month, puts your meets on your own results page, and one plan covers every phone.
Related
What frame rate do you need to film a sprinter?
Ordinary video is fine for checking posture. Ground contact time and cadence need enough frames to actually catch the foot going on and off the track.
Read →Why does my sprinter take short, choppy strides even though they're fast?
A fast sprinter with a short stride is usually winning on turnover, and turnover has a ceiling a longer stride does not.
Read →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.
Read →Try it: Sprint timer app: 40-yard dash and flying sprints with one phone