The ability to accelerate the legs faster, or produce force quicker against the ground when sprinting requires the activating muscles to be recruited and relaxed in a shorter time, providing the force produced by the muscle remains the same or higher.
I enjoyed Jeremy Richmond’s thought provoking article and I suggest reading it. One question is, does HRV relate to local fatigue? System fatigue of the nervous system is important, but because of the fiber distribution and biomechanical loading things fatigue differently. So HRV is more global. Most athletes in sprinting talk about tightening up before power drop, hinting that drops in velocity are second to drops in rise and fall times.Ground contact times are signatures to pre-fatigue, the time period that is right before power decay. Listening to ground contact time is great for sprints but grass sports have no way of knowing and fatigue should be managed with good record keeping.