Studies have shown an association between vigorous physical activity and amyotrophic lateral sclerosis (ALS). Now a new study has suggested that it is the occupational physical activity, and not leisure time physical activity like walking, cycling etc. which is a risk factor for ALS.

The study reported in the journal Neurology involved 393 persons with a recent diagnosis of ALS. The control group included 791 persons, who did not have ALS.

All the participants were instructed to complete a questionnaire detailing the type of and amount of work and leisure time activity they got when they were 20, 30, 40, 50 and 60 years old. Physical activity was categorized into two based on the amount and intensity of the activity. Sweaty activity, which involved sports or heavy physical work (occupational physical activity) and light activity (leisure time physical activity), which included activities like walking, cycling or light physical activity. Each hour of sweaty activity was given eight metabolic equivalents (METs), while each hour of light physical activity was allocated three METs.

Total physical activity did not show an association with risk of ALS risk when activity levels up to five years before the study began, were examined. Both people with and without ALS logged in an average of 17-18 MET hours per week of total physical activity. A sharp decrease in physical activity was observed in persons with ALS five years before their diagnosis suggesting that the disease process starts much earlier than it manifests and becomes clinically evident.

The risk of developing ALS was 2-folds higher in persons engaged in heavy occupational work (OR 1.97), while no such association was observed for persons with light physical activity on the job. Twenty-two percent of persons with ALS had occupations that required heavy physical activity in comparison to 13% of those without ALS. This association persisted even after adjustment for other probable risk factors such as age, sex, smoking.

Level of physical activity was also found to have an impact on the survival of patients with ALS.

Sedentary persons and those who had the highest activity levels (25 MET hours per week, or the equivalent of biking or walking about 5 hours per week) had the lowest survival time post-diagnosis; 15.4 months and 19.3 months, respectively.

Persons who engaged in around 11 MET hours per week of physical activity, equivalent to cycling or walking for 2 hours a week, had the best average survival rate. ALS patients who logged in this amount of physical activity at the time of their recruitment into the study survived for average of 29.8 months after diagnosis.

ALS is a progressive neurodegenerative disease; it is a rare disease. The usual life span after diagnosis is 2-5 years. Perhaps the most famous person with ALS was Stephen Hawking, who defied the odds and survived his diagnosis for 55 years.

Although the study did not establish a cause-and-effect association, it did find that the risk of ALS was increased with intense physical activity that occurs during work. Both inactivity and high activity levels adversely affected survival of persons once they had been diagnosed with ALS indicating that intensity of physical activity may be a disease modifying factor. Moderate exercise is beneficial for ALS patients.

Reference

1. Rosenbohm A, et al. Life course of physical activity and risk and prognosis of amyotrophic lateral sclerosis in a German ALS Registry. Neurology Oct 2021, 10.1212/WNL.0000000000012829; DOI: 10.1212/WNL.0000000000012829.
2. American Association of Neurology (AAN) News release, October 20, 2021.