Gentle, graded exercise can alleviate the symptoms of some people with myalgic encephalomyelitis (ME), also known as chronic fatigue syndrome, scientists have stressed.
People with ME sometimes fear physical activity can worsen their symptoms.
Reporting in the Lancet Psychiatry journal, scientists investigated how such concerns influenced the success of exercise therapies.
Charities stress there is no one-size-fits-all treatment.
About a quarter of a million people have ME in the UK, but there has been much debate about the most appropriate treatments. And the cause of the condition remains unknown.
- severe tiredness
- poor concentration
- disturbed sleep
- muscle and joint pain
Treatments offered on the NHS include:
- cognitive behavioural therapy - changing how people think and act
- graded exercise therapy - gradually increasing the amount of exercise a person does
But for many years people focused on adaptive pacing therapy - planning activity carefully to avoid fatigue.
A team of British researchers found behavioural and exercise therapies were better at reducing fatigue and disability than adaptive pacing strategies.
And a separate analysis by scientists from London and Oxford suggests these treatments work by helping people overcome fearful thoughts and behaviours - such as avoiding exercise in the belief it could make things worse.
Researchers say both beliefs and behaviours play a part in perpetuating fatigue and disability.
Sonya Chowdhury, from the charity Action for ME, said this did not mean it was a psychological illness.
"Nor do we believe that people with ME are afraid of taking part in appropriate activity or exercise - appropriate activity might involve a short walk or for someone with severe ME, small movements or even sitting up in bed.
"Fear avoidance is a well-documented factor that can affect the experience of any chronic pain condition, regardless of pathology."
She pointed out that people with the most severe form of the disease, who are bed-bound, had not been included in this research.
Experts advise gradual increases in activity such as walking, working towards the more general recommendation of 30 minutes of physical exercise, five days a week.
They say it is important exercise therapy is carried out by trained staff and that both extreme activity and excessive rest are avoided.