How robust is ACTIVLIM for the follow-up of activity limitations in patients with neuromuscular diseases?

•ACTIVLIM: a valid and accurate measure of activity in neuromuscular diseases.•ACTIVLIM is consistent across age, gender, language and time in a nationwide case mix.•ACTIVLIM allows clinically meaningful follow-up of children and adults.•A slight decrease in activity over one year is shown in most neuromuscular diseases.•Over 1 year, level of activity is most decreased for ALS and most increased for CIDP.