Low-intensity aerobic exercise can increase energy levels and decrease fatigue, finds a new study.

Researchers at the University of Georgia found that when a group of sedentary people were exposed to low-intensity aerobic exercise for 20 minutes three times a week for six weeks, their fatigue levels dropped by 65 per cent and their energy levels rose by 20 per cent.

Thirty-six healthy young people took part in the study. All had reported persistent fatigue prior to the study, which had not been medically diagnosed as chronic fatigue syndrome. The authors believe that about 25 per cent of the population suffers from this type of fatigue.

Another group that engaged in moderate intensity aerobic exercise for the same period had a 20 per cent increase in energy levels but only a 49 per cent decrease in fatigue.

"It could be that moderate-intensity exercise is too much for people who are already fatigued," said Patrick O'Connor, a co-author of the study and co-director of the UGA Exercise Psychology Laboratory, in a release. "And that might contribute to them not getting as great an improvement as they would had they done the low-intensity exercise."

The authors theorize that exercise causes the central nervous system to increase energy and reduce tiredness.

The authors say that people who feel tired should see exercise not as a fatiguing but as an energizing activity.

"Too often we believe that a quick workout will leave us worn out — especially when we are already feeling fatigued," said lead author Tim Puetz. "However, we have shown that regular exercise can actually go a long way in increasing feelings of energy — particularly in sedentary individuals."

The study is in the February issue of the journal Psychotherapy and Psychosomatics.