Comment by nonameiguess

It's long been found in exercise research that exercise itself attenuates many of the negative effects of sleep restriction. This might also explain why the military can get away with such poor sleep, because of the hard standards on minimum aerobic fitness required to even wear the uniform, and the fact that the infantry and special operators experiencing the worst sleep deprivation are also the people in the best shape. There are plenty of other adaptations you get out of aerobic exercise (capillarization, eccentric heart hypertrophy, increased red blood cell count, localized muscular endurance), but the most important and durable adaptation is more efficient mitochondrial function.