Physical activity has always been at the forefront of factors associated with MND, but studies investigating its effect have often been conflicting. The reason why we might see contrasting results is often due to different cohorts and numbers of people included in the study, the method by which the data was collected, or the types of questions asked and the way they were presented. Increased number of studies on the same topic might then improve the way these are conducted in the future and provide more reliable conclusions.
The most recent multi-centre study that included over 1,500 people with MND and nearly 3,000 control participants was conducted by the Euro-MOTOR consortium under the leadership of Prof Leonard van den Berg. Today (24 April), the group published a paper on their findings in the Journal of Neurology, Neurosurgery and Psychiatry . The study collected data using thorough questionnaires, presented to Dutch, Irish and Italian participants either face-to-face or on paper, asking about their exposure to smoking, alcohol, and the type and amount of physical activity throughout their lifetime – both occupational and leisure. A score was then assigned to each person based on the amount of energy expenditure each activity requires – this is called metabolic equivalent of task (MET).
Aside from showing that people with MND smoked more and drank less alcohol compared to control participants, a significant positive relationship between physical activity and likelihood of MND was confirmed, shown by an odds ratio (OR) for all physical activities of 1.06 (1.07 for leisure time activities only). This statistic represents the ‘odds’ of a risk effect (here, physical activity) occurring in one group compared to another, where an OR of 1.0 shows no difference between the groups, OR greater than 1.0 shows increased risk and any score below 1.0 shows reduced effect in the test group = protective effect. In effect, this means that there was a 6% increase in risk to people with high activity levels.
While main focus was on the association of physical activity and the risk of developing MND, other analyses were ran to explore the relationship even further. The researchers looked at whether the relationship is affected by (a) gender, (b) presence of C9orf72 repeat expansions, (c) educational level, (d) hours per week, start and stop time of physical activity, (e) onset of the disease: i.e. bulbar or spinal, and (f) age of disease onset. None of these factors were shown to impact the results and affect the OR of the relationship.
The authors also pointed out that exposure to potential factors during leisure and occupational physical activities (e.g. exposure pesticides) is unlikely to drive the relationship between MND and physical activity and it is rather the direct effect of physical activity that causes the association (and not a side effect of another factor).
While this study adds to the cumulative evidence that physical activity is associated with MND, it is crucial to say that it is not a major factor in the development of the disease. Rather, it is another risk factor that together with others (including genetics) may increase the chances of MND development. It is likely that physical activity is only a risk factor in the presence of certain genetic profile, making some people more susceptible to motor system damage.
It is important to note that the take-home message of this study isn’t to stop exercising as the benefits of exercise greatly outweigh the potential negatives, especially when we consider the the high odds of developing cardiovascular diseases due to sedentary lifestyle.
To find out more about previous studies investigating the link between physical activity and MND, see our previous article Physical activity and MND – is there a link?