The relationship between sleep quality and recovery is pretty well known in exercise circles. A lot of "amateur" elites, like very competitive marathon runners

The relationship between sleep quality and recovery is pretty well known in exercise circles. A lot of "amateur" elites, like very competitive marathon runners that take it quite serious around a day job, have to work in long low intensity cardio workouts around their schedules, so you start thinking very hard about recovery. When you think about recovery that hard you also start prioritizing sleep a lot, especially if you're up at 4am for a 2 hour run, for example. Missing a lot of sleep for successive days is almost guaranteed to lead to injury when you're training very hard. The effect on your cardio performance (even just average BPM) can be stark. I don't know how some resident doctors, for example, can also be very good marathon runners. Just managing that sleep schedule must be crazy.