In adults, muscle diseases are usually chronic long-term conditions that do not have a definitive cure. Supportive care has been shown to reduce complications from muscle disease and improved survival in some cases. However, there has been limited research to evaluate interventions that may improve quality of life (QoL) with this patient group. The QoL of those with MD is not just affected by the severity of their MD but also a variety of psychological variables. Based upon the knowledge of these psychological variables the investigators feel that a particular type of psychological intervention known as "acceptance and commitment therapy" (ACT) could potentially improve QoL in those with MD. The investigators therefore propose to test whether ACT does in fact improve QoL in those with MD by randomising 154 patients to receive either standard medical care plus a guided self-help ACT programme, or standard medical care only.

Previous research has shown that while QoL is determined by the severity of the MD, this does not explain all aspects of the reduced QoL of those with MD. Previous research suggested that a cognitive behavioural approach using Acceptance and Commitment Therapy (ACT) would best suit those with MD. A pilot study of this approach in seven participants with MD was promising, and has led to this definitive trial of ACT. The aim of this study is to determine the efficacy of an ACT intervention to improve the QoL of individuals with MD.

Patients with one of the following muscle diseases will be recruited: limb girdle muscular dystrophy, dystrophinopathies resulting in a Becker' muscular dystrophy phenotype, facioscapulohumeral muscular dystrophy and inclusion body myositis. Patients will be recruited primarily through muscle clinics at King's College Hospital (KCH) and The Royal London Hospital (RLH) but also via Muscular Dystrophy UK (MDUK) and UK registries of patients with these muscle diseases.

Inclusion Criteria:

1. Diagnosed with one of four specific muscle diseases on the basis of diagnostic criteria:

   1. Limb girdle muscular dystrophy; symptomatic limb girdle muscular dystrophy genetically or pathologically proven
   2. Dystrophinopathies resulting in a Becker' muscular dystrophy phenotype (excluding Duchenne muscular dystrophy) with pathology or genetic diagnosis
   3. Facioscapulohumeral muscular dystrophy diagnosed clinically with specific genetic abnormality in the subject or their family
   4. Inclusion body myositis clinic-pathologically defined, clinically defined or probable IBM based on ENMC research diagnostic criteria 2013 (submitted)

2. duration of muscle disease greater than six months

3. over the age of 18 years

4. access to the internet and a computer on which they can receive the intervention materials

5. HADS scores > 8 for depression or >8 for anxiety

Exclusion Criteria:

1. Major active co-morbidities unrelated to muscle disease such as arthritis, respiratory disease, cardiovascular disease

2. Unstable complications of muscle disease including:

   1. neuromuscular respiratory weakness
   2. cardiomyopathy

3. Cognitive impairment that prevents comprehension of the questionnaires; assessed using the Montreal Cognitive Assessment

4. Unable to read English questionnaires

5. Major diagnosed active mental health co-morbidities e.g. psychosis, major depression, obsessive compulsive disorder, active suicide risk

6. Current or recent participation in other treatment intervention studies (< 4 weeks after completion)

7. Currently receiving psychological support or psychotherapy