Federated sport activity in amyotrophic lateral sclerosis: a case-control study

Amyotrophic lateral sclerosis (ALS) develops in a multistep process combining environmental variables and genes. Among the identified risk factors, the role of regular vigorous physical activity is still debatable. Objective: This case-control study investigated the relationship between ALS and different degrees of sports engagement, with federated status as a proxy for strenuous activity. Methods: 586 ALS patients and 558 controls were consecutively assessed by using a standard questionnaire. Due to low female participation in regular or intensive sports activity, the study focused on men (327 with ALS and 314 controls). Results: Overall, football (soccer) had the most practitioners (n = 137, 35.8%), accounting for 62.1% of ALS and 32.3% of control federated athletes. Male football players have a 3.07-fold increased ALS risk (95% CI: 1.82-5.19) compared to other men (p < 0.0001) and 3.43-fold increase (95% CI: 1.77-6.68) compared to those federated in other sports (p = 0.0003). After controlling for age and trauma, football players still had 2.91-fold (95% CI: 1.70-5.01) increased risk compared to non-federated and non-participants in contact sports intensively. No significant ALS risk difference existed for other sports practiced with identical intensity and contact levels. Clinical characteristics of ALS federated football players were similar to other ALS patients. Conclusion: Our results suggest ALS susceptibility is not linked to general physical activity, but specifically to competitive football, regardless of a history of head and neck trauma. Given football's popularity, even a small risk increase could impact many. Further research is required to understand the mechanisms linking football to ALS, and why this association is not observed in other sports.