The sleep cycle changes during puberty. And this means that the time of day makes a dramatic difference in the athletic performance of teens.

That's the conclusion of Brown University psychiatry professor Mary A. Carskadon, PhD, director of the chronobiology and sleep research lab at E.P. Bradley Hospital in Providence, R.I. In a review of sleep research on teens, she notes that with puberty come big changes in the human sleep cycle.

Some experts say teens need more sleep than younger children need. Carskadon, an expert in sleep and teen development, says this isn't so. At puberty, she says, teens' nightly need for sleep actually drops a bit. But that's generally a moot point, as few teens come even close to getting enough sleep.

"Young people live in a nearly constant state of chronic insufficient sleep," Carskadon writes in the April issue of Clinics in Sports Medicine.

Internal Teen Clock Out of Sync With Alarm Clock

Part of the problem is that puberty throws the sleep cycle out of whack. Instead of aligning sleepiness and wakefulness with the 24-hour external clock, Carskadon suggests, teens align with an "internal day."

Other things are going on, too. Teens may need more than nine hours of sleep, but as they enter puberty they find they are better able to resist the urge to sleep. And in their rooms they find all kinds of stimulating activities — the Internet, television, and computer games, for example. Meanwhile, the clock ticks toward the early morning school schedule.

"A teenager's need for sleep appears just about identical to when he or she was a preteen, even though nearly every teen succumbs to the adolescent lifestyle — and the constraints of school schedules — by getting less sleep than required on most school nights and partially compensating by oversleeping on weekend days," Carskadon writes.

Teen Sleep and Teen Athletics

This means that before puberty, kids who get enough sleep will be alert in the morning and wide awake all day. After puberty, a teen who got enough sleep would be alert for about eight hours. Then there would be a midafternoon drop in alertness and performance, which would soon reverse as the teen's timing system once again swings toward wakefulness.

Before puberty, kids who don't get enough sleep get most tired in the afternoon and evening. Teens who don't get enough sleep have a different problem — one familiar to almost every parent.

Teens who don't get enough sleep "are extremely impaired in the morning." That's because they've had little restorative sleep to buffer the effects of waking just as their internal clocks make them least alert. But later in the day — despite too little sleep — teens get a jolt of energy as their internal clocks make them most alert. And, of course, teens try to make up for their sleep deprivation by sleeping late on weekends. This may help in the short term, but it is a disaster in terms of finding a healthy, regular sleep schedule.

All this has a profound effect on athletic performance. Carskadon concludes that:

— Before puberty, children and young teens function better early in the day than in the afternoon and evening.

— During and after puberty, teens perform worst in the morning.

— All kids' performance benefits from routine, adequate sleep on a regular schedule.

— Teen teams that travel west across time zones have an advantage early in the day.

— High school or college teams that take long training trips are likely to have schedule problems when they come home. This is especially true for teams on the East Coast that travel west.

Many adults take melatonin supplements to help them adjust to jet lag or as a sleeping aid. Carskadon warns that melatonin may be dangerous for teens as it may delay normal development during puberty.

By Daniel J. DeNoon, reviewed by Michael W. Smith, MD

SOURCE: Carskadon, M.A. Clinics in Sports Medicine, April 2005; vol 24: pp 319-328.