Why is this review important?
The term 'muscle disease' comprise a heterogeneous group of conditions affecting predominantly the skeletal muscles but may also involve other systems. Synonymous terms of muscle disease are myopathy, myopathies, myopathic condition and muscular disorder. They can be acquired, congenital and/or familial with a diversity of causes. Muscle disease affects patients’ function at many levels making it challenging to plan interventions and predict its prognosis.
Physical fitness training is defined as a planned, structured regimen of regular physical exercise deliberately performed to improve physical fitness, cardiorespiratory fitness, and body-composition. Strength training is aimed to improve muscle strength and endurance, whereas aerobic exercise to improve cardiorespiratory endurance, optimising physical fitness and preventing further muscle wasting.

Who is it relevant for?
Persons with muscle disease, caregivers, professionals and researchers, general physicians and policy makers.

What is it about?
The aim of this review was to assess the effects (benefits and harms) of strength training and aerobic exercise in people with a muscle disease. 
The analysis included 14 randomized trials published till November 2018, focusing on aerobic exercise (five), strength training (three), or both exercises (six) with training duration from eight to 52 weeks. Total participants were 428 with facioscapulohumeral muscular dystrophy, dermatomyositis, polymyositis, mitochondrial myopathy, Duchenne muscular dystrophy, or myotonic dystrophy. 
Outcomes analysed included: (i) muscle strength, (ii) aerobic capacity (physical work capacity, oxygen consumption, cardiac function and/or respiratory function), (iii) muscle performance (like 6-minute walk test), (iv) quality-of-life measures (like Short Form 36), (v) pain (analogue pain scale), and (vi) adverse effects requiring withdrawal of the participant from the study (increase in pain, injury, etc.).   

Authors’ conclusions
The evidence regarding strength training and aerobic exercise interventions remains uncertain. Evidence suggests that strength training alone may have little or no effect, and that aerobic exercise training alone may lead to a possible improvement in aerobic capacity, but only for participants with facioscapulohumeral muscular dystrophy. For combined aerobic exercise and strength training, there may be slight increases in muscle strength and aerobic capacity for people with dermatomyositis and polymyositis and a slight decrease in aerobic capacity and increase in muscle strength for people with juvenile dermatomyositis. More research with robust methodology and greater numbers of participants are required.

Future perspective
There is a need of further studies to establish whether strength training is beneficial in all forms of muscle diseases. Authors recommend that participants with different muscle disorders can be involved but data needs to be presented for each major type of muscle disease separately. The research design needs to be randomised controlled, blinded, with details defined for intervention-strategies, duration of minimum six weeks, intensity-frequency of training, post-training effects, long-standing effects after-training is finished. Outcomes also need to include details for measures muscle strength, endurance, functionality, pain, adverse-effects and quality of life

Comment by Sunita Gudwani