A new study indicates that this effect may stem from an individual`s sense of mastery over - or belief in his or her ability to achieve - certain physical goals.

`We base our arguments on fatigue being a symptom of depression,` said Edward McAuley, professor of kinesiology and community health at the University of Illinois who led the study.

This belief in one`s own abilities is called self-efficacy, McAuley said. The conviction that you can jog down the block or climb several flights of stairs without stopping is an example of self-efficacy.

Previous studies have shown that increases in physical activity increase self-efficacy. The effect is almost immediate, McAuley said.

`The evidence is monumental that physical activity has some effect on well-being,` McAuley said. `The question is: Why?`

He and his colleagues wanted to determine whether self-efficacy plays a role in the sequence that leads from physical activity to reduced depression and fatigue.

To test this hypothesis, researchers re-analysed data from two previously published studies, the first involving breast-cancer survivors and the second focusing on individuals diagnosed with multiple sclerosis.

Both studies included self-report questionnaires, but the second used different measures of health status, physical activity, self-efficacy, depression and fatigue, said a university press release.

A statistical analysis showed that in both groups, higher levels of physical activity corresponded to higher self-efficacy and lower levels of depression and fatigue.

The study appears in Psychosomatic Medicine.

Source: IANS