London, Dec 14 (IANS): Engaging in moderate physical activity including walking, cycling or jogging in the evening does not cause sleep problems, suggest researchers.

The research challenges previous studies that suggested that sleep quality can be improved by avoiding exercise in the evening.

The findings showed that doing exercise for four hours before going to bed does not have a negative effect on sleep.

However, vigorous training within an hour before bedtime may have a negative effect on sleep.

"If doing sport in the evening has any effect on sleep quality at all, it is rather a positive effect, albeit only a mild one," said Christina Spengler, Deputy Head from the ETH Zurich in Switzerland.

In the study, published in the journal Sports Medicine, a small group of people after taking part in some kind of sport in the evening, spent 21.2 per cent of their sleeping time in deep sleep, compared to 19.9 per cent following an evening without exercise.

However, those who completed an intensive training session shortly before bedtime took longer to fall asleep.

The reason could be because they were not able to recover sufficiently in the hour before they went to bed. Their hearts were still beating more than 20 beats per minute faster than their resting heart rate.

Although the difference is small, it is statistically significant. Deep sleep phases are especially important for physical recovery, the researchers noted.

"Moderate exercise did not cause sleep problems in any of the studies examined, not even when the training session ended just 30 minutes before bedtime.

"However, vigorous training or competitions should be scheduled earlier in the day, if possible," said Jan Stutz, doctoral student at the varsity.