RT Journal Article SR Electronic T1 Physical activity as a risk factor in ALS JF Journal of Neurology, Neurosurgery & Psychiatry JO J Neurol Neurosurg Psychiatry FD BMJ Publishing Group Ltd SP jnnp-2018-318147 DO 10.1136/jnnp-2018-318147 A1 Michael Swash YR 2018 UL http://jnnp.bmj.com/content/early/2018/04/25/jnnp-2018-318147.abstract AB