Why does my runner's cadence drop in the second half of a race?
Pace is cadence times stride length, and when a runner tires it is usually the turnover that goes first, not the stride.
A distance runner's first lap looks sharp and the last one looks like somebody else running. Ask what changed and most coaches say the legs got tired, which is true but not useful. The specific thing that usually changes is cadence, how many steps the runner takes per minute, not stride length.
Speed has two levers, and fatigue pulls on one of them harder
Pace is cadence multiplied by stride length. When a runner tires, stride length tends to hold up longer than cadence does, because a long stride can be partly passive while a fast leg turnover takes continuous muscular effort to drive. So cadence drops first, pace drops with it, and the runner's stride can even look about the same length on video while the clock says they have slowed down.
What is usually behind the drop
- Hip flexor and quad fatigue slowing how fast the recovery leg swings back through, which caps how often the foot can land no matter how willing the runner is.
- A pacing mistake, running the first half faster than the body can sustain, so the second half is spent recovering from a debt rather than racing.
- A mental letdown once the lead changes or the race feels decided, which shows up as a slower turnover before the runner consciously feels slower.
Checking it rather than guessing it
The sprint setting in the Film Room reports cadence, along with ground contact time and flight time. Clip the first lap and the last lap of the same race and set them side by side. A cadence that has dropped by more than a handful of steps a minute, with ground contact time stretching out at the same time, points at fatigue in the push. A cadence that held steady while the stride itself got shorter points somewhere else, usually pacing or focus.
A single 2D camera can tell you that cadence dropped and by how much. It cannot tell you whether that came from a muscle that is actually fatigued, a runner who mentally let go, or a race that was paced wrong from the gun. That is still a conversation, not a number.
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Related
Why does my runner's stride get shorter while their cadence stays the same?
A steady step count can hide a stride that is quietly getting shorter as a runner tires, and cadence alone will not tell a coach the difference.
Read →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.
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 →Try it: Running form analysis app: skeleton, form check, speed and cadence from a phone clip