There is little consensus about measurement of physical activity in adults with muscular dystrophy. This systematic review summarizes evidence for measurement properties of direct and indirect measures of physical activity in adults with muscular dystrophy. A two-phase search for peer-reviewed articles identified firstly, studies which measured physical activity in this population and secondly, studies reporting the measurement properties of activity measures. Methodological quality was assessed using COSMIN guidelines and a best evidence synthesis conducted. Phase 1 included 53 studies identifying 63 measures including accelerometers, direct observation, heartrate monitors, calorimetry, positional sensors, activity diaries, single scales and questionnaires. Phase 2 included 26 studies of measurement properties for 32 measures. Methodological quality of the included studies was low, only 2 were rated good. There was insufficient evidence to robustly recommend any physical activity measures and further research is required to validate measures of physical activity for adults with muscular dystrophy. Based on the findings of this review, measures with potential for further study have been highlighted.