Physical activity in amyotrophic lateral sclerosis: a systematic review of the methodologies used to assess a possible association.

Growing evidence suggests that strenuous physical activity (PA) may be associated with an increased risk of developing Amyotrophic Lateral Sclerosis (ALS), a fatal neurodegenerative disease. However, there are inconsistent findings across studies that may reduce our understanding of any potential associations. We propose that these differences may reflect the tools used to record historical PA. We conducted a systematic review evaluating the risk of developing ALS due to PA. The inclusion criteria were met by 22/113 studies, and an association between increasing PA and ALS was found in 15 studies. Studies that found a positive association were more likely to have longer recall periods and convert data into Metabolic Equivalent of Task values. Studies that did not find an association with increasing PA were more likely to use questionnaires with no validity or reliability data. Questionnaires with validity data all showed at least a moderate correlation of PA compared to objective measures, with reliability ranging from poor to good. Study designs included prospective cohort and case-control, which may also contribute to heterogeneity in findings. This work highlights the need for consensus on the type of questionnaire to use to assess potential associations between PA and ALS.