This is one of life's impossible questions, and as you may have guessed, the answer is complicated. "Obviously, you want to do both, get sufficient sleep and be physically active — that would be ideal," says Christopher Kline , PhD, assistant professor in the department of health and physical activity at the University of Pittsburgh, and spokesperson for the American Academy of Sleep Medicine. But we only have 24 hours in a day, and most of those hours are jam-packed with responsibilities, which means we have to allocate our time wisely. And it often comes down to weighing the benefits of exercise with the benefit of having an hour more of sleep, he says.