Charlie Francis, coach of Ben Johnson, the former fastest man in the world, writes in his 1990 book Speed Trap (p.62, bold mine, italics his):
To reduce the risk of injury, I regularly massaged my sprinters, especially before their speed work. By loosening their muscles, massage enhanced their performance and removed lactic acid and other fatigue by-products from their muscles. Massage also gave me an added safety check. None of my kids ever wanted to skip a speed run. If I asked if they felt tight, they'd deny it. But their muscles couldn't lie, and a massage often clued me to pull an athlete out of a run before something went wrong.
In the quest for speed, touch is truth!
Further on, Francis describes a different method (p.73, bold mine, italics his):
In distance running, oxygen uptake and lactic acid tests can help a coach keep track of his athletes' aerobic capacity. These tools are useless, however, for anaerobic events like sprinting; there is no machine to gauge central nervous system fatigue. My feedback came from my athletes, and so I'd constantly ask if they felt as if they needed to rest. But since mature athletes tend to ignore signs of fatigue and incipient injury–believing, as I used to, that more work is better–I couldn't always trust their responses. To protect them from themselves, I would listen to their footfalls during a drill. If the sound became louder, it told me the runner's hips were dropping. The drop might be as little as a sixteenth of an inch, beyond the discernment of eyes or cameras, but my ears would tell me that fatigue had set in, and that it was time to curtail the work-out.
This reminds me of an earlier post in which I suggested that the surveillant gaze can be vulnerable at high speeds. In training sessions, Francis overcomes this vulnerability literally by listening.
As we move to the competition stadium, though, where the stakes get higher, we turn to electronic devices to provide the haptic and acoustic assistance required to "see" the athletes and determine truth.
McLuhan, Understanding Media: "Moving from print to electronic media we have given up an eye for an ear."