Physical activity, and physical activity related to sports, leisure and occupational activity as risk factors for ALS: A systematic review

Background: Amyotrophic lateral sclerosis (ALS) is considered a multifactorial, multisystem neurodegenerative disease due to an interaction between environmental and genetic factors. This systematic review aims at gathering all available evidence on the association between physical activity (PA) and the risk of ALS. Methods: Relevant literature published up to January 2015 was gathered through structured searches on Medline, The Cochrane Library, and the ISI Web of Science databases. Studies considering any type of PA as the main exposure and a diagnosis of ALS or motor neuron disease were selected. Data were extracted in standardized forms, and the quality of included studies was assessed using the Newcastle-Ottawa Scale (NOS). Results: Bibliographic searches yielded 3168 records. Nineteen case control studies and 7 cohort studies met the inclusion criteria, and were included in the analysis. Evidence on cumulative measures of PA as a risk factor for ALS remain inconclusive. However, cohort studies report a significantly higher number of cases of ALS in professional soccer and American football players, and a slightly increased risk of ALS in varsity athletes.