An international team, led by the Walter Reed Army Medical Centre in the US, has found that exercising during the day can keep people awake at night instead of putting them to sleep, 'The Daily Telegraph' reported.

Researchers have based their findings on an analysis of an experiment involving 14 people – who wore armbands – monitoring their movements for 23 days.

The study found the more active they were the less they napped. Surprisingly, total sleep time increased by an average of 42 minutes a night after days with low activity, the findings revealed.

In fact, the data collected included total sleep time, exercise energy expenditure and BMI of the participants, seven of whom were a normal size with the others overweight. The increased activity was seen in the group with a higher BMI who also walked more.

"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," lead researcher Dr Arn Eliasson said.