What is the PACE trial?
This large-scale trial is the first in the world to test and compare the effectiveness of four of the main treatments currently available for people suffering from chronic fatigue syndrome (CFS), also known as myalgic encephalomyelitis (ME). These are adaptive pacing therapy, cognitive behaviour therapy, graded exercise therapy, and standardised specialist medical care (see below). All of the treatments offer ways for patients to deal with and improve the symptoms of CFS/ME and its effects on disability. The participants in the trial are randomly allocated to one of the treatments and then given a 12-month programme involving appointments with specialised doctors and, for three of the four treatment groups, therapists. Participants' progress is closely monitored by specially-trained research nurses or assistants. The five-year trial will involve 600 participants, aged 18 and over, in Scotland and England. All have to be referred from the specialist hospital CFS/ME clinics involved in the trial and these are based in Edinburgh, Oxford and three London hospitals.

What is CFS/ME?
CFS/ME is a common disorder. Estimates vary, but it is believed that between one in 40 and one in 250 of the population will suffer from the illness at any one time. CFS/ME causes disability as a result of persistent, abnormal tiredness which is made worse by activity. Other symptoms can include disturbed or unrefreshing sleep, or sleeping for longer, problems concentrating or remembering, pain in the muscles and/or joints, headaches, sore throats and tenderness in the neck. The diagnosis of CFS/ME sometimes can be difficult because it requires that a large number of other possible causes of the symptoms, such as thyroid gland disease and severe depression, are excluded.

What are the treatments being tested?
The four treatments are standardised specialist medical care (SSMC) alone, SSMC plus adaptive pacing therapy, SSMC plus cognitive behaviour therapy and SSMC plus graded exercise therapy. The therapies are delivered, as appropriate, by occupational therapists, physiotherapists, clinical psychologists or by other healthcare staff with specialist training.

• Standardised specialist medical care. This is the most common treatment for CFS/ME. Specialist doctors can give an explanation of why participants are ill and general advice about managing the illness. They may also prescribe medicines to help with troublesome symptoms such as insomnia and pain, or advise GPs on what medicine is appropriate. If a participant is randomised to this treatment alone, they are encouraged to use specific self-help management that make most sense to them.
• Adaptive pacing therapy. This therapy is about carefully matching activity levels to the amount of energy available. Therapists work with participants in this treatment group to help monitor activity and symptoms, aiming to improve quality of life and create the best conditions for a natural recovery.
• Cognitive behaviour therapy. This therapy is about examining how thoughts, behaviour and CFS/ME symptoms interact with each other. Between therapy sessions, participants in this treatment group are encouraged to try out new ways of coping with their illness.
• Graded exercise therapy. This is about gradually increasing physical activity to improve fitness and get the body used to activity again. A therapist helps participants in this treatment group to work out a basic activity routine and slowly build up the amount of exercise as fitness increases.