Strenuous physical activity is associated with a younger age of amyotrophic lateral sclerosis onset in two independent cohorts.

Amyotrophic lateral sclerosis (ALS) is a complex neurodegenerative disease characterized predominantly by degeneration of both upper and lower motor neurons, thought to occur due to an interplay between genetics and environmental factors. Physical activity has been suggested as a potential risk factor for ALS; however, the exact role of exercise in the onset and progression of the disease is still unclear. We assessed lifetime physical activity in two independent ALS cohorts: post-mortem brain donors from the London Neurodegenerative Diseases Brain Bank (n = 139) and patients from the Motor Neurone Disease (MND) Register of England, Wales and Northern Ireland (n = 166 cases, 196 controls). In both cohorts, highly active individuals developed ALS symptoms at a significantly younger age, 54.2 years (mean, standard deviation = 7.5) in the post-mortem cohort and 58.0 years (median, interquartile range = 15) in the MND Register, compared with 63.9 years (mean, standard deviation = 11.5) and 63.0 years (median, interquartile range = 17.5) in inactive individuals, respectively [one-way analysis of variance (ANOVA), F(2, 136) = 6.10, P = 0.003, η 2 = 0.08, 95% confidence interval (CI) 0.02-1.00 and Kruskal-Wallis, H(2) = 7.39, P = 0.02, η 2 = 0.03, 95% CI 0.003-0.12]. Cox regression showed a higher hazard of earlier onset in highly active patients [post-mortem: hazard ratio (HR) 2.84, 95% CI 1.55-5.26, P = 0.0008; MND Register: HR 2.34, 95% CI 1.30-4.23, P = 0.005]. Our findings suggest that strenuous physical activity may be associated with a significantly younger age of ALS onset, replicated in both the post-mortem and MND Register cohorts, but not with an increased risk of developing ALS. Logistic regression analysis confirmed that neither highly active [odds ratio (OR) 1.43, 95% CI 0.69-2.99, P = 0.333] nor being active (OR 1.30, 95% CI 0.72-2.37, P = 0.386) was significantly associated with ALS risk, whereas a history of head injury was (OR 1.72, 95% CI 1.03-2.88, P = 0.038). These results suggest that strenuous exercise may accelerate disease onset in predisposed individuals, while the role of head injury requires further study and the findings may in fact indicate reverse causality.