Sleep is like a secret weapon for runners. While most athletes focus on training plans, nutrition, and gear, the most powerful performance enhancer might be the one we often overlook: a good night's rest.

Consider Sara Hall, one of America's most accomplished marathoners.

With a 2:20 personal record—that's running at a blistering 5:20 pace per mile for 26.2 miles—she represents the pinnacle of distance running achievement. Her journey began in ...