While a 2017 review found that exercise improves sleep quality and duration, working out right before bed may actually cause your sleep to suffer. "Your circadian clock and metabolism are connected. Exercise revs up metabolism, and it can stay elevated for hours, keeping you awake," Mary Ellen Wells, PhD, director and assistant professor of neurodiagnostics and sleep science at the University of North Carolina School of Medicine, told POPSUGAR. "For this reason, avoid exercise a few hours before bedtime."