GPS tracking. I went to a seminar 8-10yrs ago and they showed us what could be done with one stitched into every player's shirt. Where they run, how fast they do it etc.
Further to your point, the lecturer gave the specific example of a great player who had been playing a 'full game' for most of his career. The analytics guys arrived, looked at the data and promptly advised exactly when in games the coaches should take him out, to preserve his overall health, based on the fact that his athletic performance and decision making fell off a cliff after that point, in game after game. It actually benefited both the team and the player to manage his workload that way.