Exercise boosts quality of sleep in teens

Exercising for more than usual may lead to improved quality and duration of sleep at night, according to a study on teenagers published Wednesday.

The study in Scientific Reports journal found that getting more exercise than normal – or being more sedentary than usual – for one day may be enough to affect sleep later that night.

It found that for every extra hour of moderate-to-vigorous physical activity, the teens fell asleep 18 minutes earlier, slept 10 minutes longer and had about one per cent greater sleep maintenance efficiency that night.

"Adolescence is a critical period to obtain adequate sleep, as sleep can affect cognitive and classroom performance, stress, and eating behaviours," said Lindsay Master, data scientist at Pennsylvania State University in the US.

"Our research suggests that encouraging adolescents to spend more time exercising during the day may help their sleep health later that night," Master said.

In contrast, the researchers also found that being sedentary more during the day was associated with worse sleep health.

When participants were sedentary for more minutes during the day, they fell asleep and woke up later but slept for a shorter amount of time overall.

"You can think of these relationships between physical activity and sleep almost like a teeter totter," said Orfeu Buxton, professor of biobehavioral health at Penn State.

"When you're getting more steps, essentially, your sleep begins earlier, expands in duration, and is more efficient. Whereas if you're spending more time sedentary, it's like sitting on your sleep health: sleep length and quality goes down," Buxton said.

While previous research suggests that adolescents need eight to ten hours of sleep a night, recent estimates suggest that as many as 73 percent of adolescents are getting less than eight.

Previous research has also found that people who are generally more physically active tend to sleep longer and have better sleep quality.

However, the researchers said less has been known about whether day-to-day changes in physical activity and sedentary behaviour affected sleep length and quality.

They used data from 417 participants in the Fragile Families and Child Wellbeing study, a national cohort from 20 US cities.

When the participants were 15 years old, they wore accelerometers on their wrists and hips to measure sleep and physical activity for one week.

"One of the strengths of this study was using the devices to get precise measurements about sleep and activity instead of asking participants about their own behaviour, which can sometimes be skewed," Master said.

"The hip device measured activity during the day, and the wrist device measured what time the participants fell asleep and woke up, and also how efficiently they slept, which means how often they were sleeping versus tossing and turning," she said.

In addition to finding links between how physical activity affects sleep later that night, the researchers also found connections between sleep and activity the following day.

They found that when participants slept longer and woke up later, they engaged in less moderate-to-vigorous physical activity and sedentary behaviour the next day.