Tough workouts don’t only tire out your muscles—they also cause brain fatigue, which ups your rate of perceived exertion. Getting more rest minimizes that exhaustion, probably by making certain brain receptors linked to mental energy less sensitive to neurotransmitters like adenosine (a depressant), says lead study author Spencer Roberts, Ph.D. candidate for exercise and nutrition sciences at Deakin University in Victoria, Australia. This allows you to push harder physically than you can when those receptors are more responsive.
To perform your best, Roberts suggests spending at least 30 percent more time in bed than you typically do for three nights before any fitness competition. In turn, you'd ideally get 30 percent more shut-eye.
The bottom line:
If that increase seems unrealistic to you, don’t worry: Most people will benefit from getting any amount of extra sleep both in general and right before a race, Roberts says.