Study participants -- five healthy students on the Stanford University men's and women's swimming teams -- maintained their usual sleep-wake pattern for two weeks and then extended their sleep to 10 hours per day for six to seven weeks.

After more sleep, athletes swam a 15-meter sprint 0.51 seconds faster, reacted 0.15 seconds quicker off the blocks, improved turn time by 0.1 seconds and increased kick strokes by five kicks. Mood and alertness improved as well.

Accumulating a sleep debt -- not obtaining each night's individual sleep requirement -- has detrimental effects on cognitive function, mood and reaction time.

"These negative effects can be minimized or eliminated by prioritizing sleep in general and, more specifically, obtaining extra sleep to reduce one's sleep debt," study lead author Cheri Mah of the Stanford Sleep Disorders Clinic and Research Laboratory says in a statement.

"While this study focuses specifically on collegiate swimmers, these results begin to elucidate the importance of sleep on athletic performance and, more specifically, how sleep is a significant factor in achieving peak athletic performance."

The findings were presented at the annual meeting in Baltimore of the Associated Professional Sleep Societies.