Working out may be bad for getting off to sleep

Exercising during the day can keep you awake at night instead of putting you to sleep, says new research from the United States.

It was believed a good workout helped to send you off by making you more tired - but it now appears the reverse is true.

A study of 14 participants who wore armbands monitoring their movements for 23 days found the more active they were the less they slept.

Total sleep time increased by an average of 42 minutes a night after days with low activity.

The findings, presented at the Associated Professional Sleep Societies' annual meeting in Illinois, suggest exercise and sleep have a more complicated relationship than many people realise.

Heart specialist Dr Arn Eliasson, who led the research, said the results were the opposite of expectations.

Quality of sleep did not improve after days of increased exertion. He said: "It has long been recommended, even championed, that getting exercise is part of the recipe for improved sleep. Our data do not support that notion.

"The longest sleep and best sleep efficiency occurred after days with low non-exercise exertion. Similarly, we expected that better-rested subjects would be more inclined to get exercise or have busier days.

"However, better rested subjects got less exercise and had less calorie expenditure. After relatively more sleep, more than six hours, all measures of exertion decreased."

The data collected included total sleep time, exercise energy expenditure and BMI of the participants, seven of whom were a normal size and the others overweight.

Paradoxically, greater activity was seen in the group with a higher BMI who also walked more.

Dr Eliasson, of the Walter Reed Army Medical Centre in Washington DC, speculated that the findings might be explained by personality types.

Individuals who are ambitious and active during the day may also be more "hyper-vigilant" at night and therefore sleep less. Low-key people who are less active may have no difficulties falling or staying asleep.

Another explanation may be that job and life stresses lead to busier days, more exertion and more calories burned but may interfere with sleep.

Previous studies have suggested exercise can help people who have sleep problems. But there have been conflicting results as to whether morning or afternoon exercise is better.

It was believed exercise improves sleep because it produces a rise in body temperature, which is then followed by a drop a few hours later.

The traditional advice has been to exercise at least three to four hours before your bedtime to give your body time to cool down. But now scientists may have to think again.

- INDEPENDENT