• Health promotion

The impact of (in)sufficient levels of physical activity (PA) have been well described and without argument, the promotion of PA—defined as moderate to vigorous physical activities, including sports and exercise—is now a cornerstone of contemporary public health.1 In our global effort to decrease the individual and public burden of chronic and lifestyle-related diseases, PA is being promoted as a medicine or drug, with the implication that it is a treatment and a preventive measure. Although the pharmacological benefits of PA have been well described,2 the analogy between PA as medicine is not drawn in full, because any substance that is capable of producing a therapeutic effect can also produce unwanted or adverse effects.3 The potential for adverse effects of PA, and the need to mitigate them, are mostly ignored in PA research and PA interventions alike.

An adverse drug reaction is defined by the WHO as “a response to a drug that is noxious and unintended and occurs at doses normally used in man for the prophylaxis, diagnosis or therapy of disease, or for modification of physiological function.”3 An injury resulting from the recommended daily dose of 30 min of moderate to vigorous PA certainly fits this definition. However, truth be told, while adverse effects of actual drugs are regulated and monitored by law, PA and its promotion are neither governed by any official administrative body nor should they be. Yet, reporting guidelines drive our research, particularly for randomised controlled trials (ie, CONSORT4) that all recognise the importance of adverse events and require them to be reported in trial reports.

Why then, if this is the best scientific practice, are adverse effects of PA not reported in most PA trials? The literature provides sufficient examples of epidemiological studies that describe the incidence and burden of PA-related injury sustained during high-intensity sports and also during recommended types of lower intensity PA. This justifies their consideration in any PA intervention.5–8 The Women's Injury study (WIN), as an example, observed a musculoskeletal injury rate of 35% (!!) in a representative sample of community-dwelling women participating in all forms of PA.6 In another study, Carlson et al7 reported age-adjusted incidences of all-cause injury from the US National Health Interview Survey. With an incidence of 29.4 injuries per 1000 respondents (95% CI 25.2 to 33.6), active respondents had a greater incidence of injury related to sport and PA than did inactive respondents (15.2/1000; 95% CI 12.1 to 18.3). This may suggest that the risk of injury in inactive individuals is low. Yet, these numbers are not corrected for hours of participation in sport (ie, injury incidence density). Consequently, while one can only sustain a sports or PA related injury while participating in such activities, the comparison between active and inactive respondents made by Carlson et al7 may be biased by actual risk exposure. Other recent studies that do take actual risk exposure into account have indicated that injury risk is increased among those who are least physically active or start to take up PA.8 ,9 The latter group of participants is of special importance, as these lower active individuals, who are inherently more susceptible to injury, are at the same time the target groups of active PA promotional efforts. Consequently, without proper interventions in place to minimise injury risk, a large group of individuals who choose to move to a healthier lifestyle will be affected by the potential adverse effects of otherwise healthy PA. Next to the general public burden of these ‘to be expected’ injuries, the burden sustained by the individual negatively affects current and future PA participation and, ultimately, the individuals’ overall health status.5

While PA is clearly not without risk of injury, the two segregated fields of PA promotion and injury prevention must combine forces. Unfortunately, this message is mostly neglected and ignored by the exercise is medicine field. As an example, the latest ‘Exercise is Medicine’ issue of the British Journal of Sports Medicine (Volume 48; Issue 3) provided a mix of articles that outlined the need for, and the positive effects of, PA on public and individual health. Yet, none of the included articles acknowledged potential side effects of their advocated medicine. Perhaps even more worrisome is the recently published IOC consensus statement on prevention and management of non-communicable disease (NCD).10 While advocating the crucial role of PA for the prevention of NCDs, no mention of injury risk or injury prevention is made in any of its messages. In fact, the word ‘injury’ is mentioned once, but only in the title of one of the cited references. The word ‘safety’ is mentioned once in the context of defining primary, secondary and tertiary prevention. The word ‘adverse’ does not appear at all.

In all honesty, in our call to acknowledge that PA is not without risk, we recognise that the risk and severity of injury due to PA at the population level may be minimal relative to the clear benefits of PA. Yet injuries still occur. Just as side effects and adverse events of clinical treatments must be disclosed, so should injury risks. Additionally, from a research perspective, we are all bound by trial reporting guidelines, which require the complete and transparent reporting of adverse effects of interventions. Simply neglecting, omitting or deliberately ignoring the word ‘injury’ in messages to promote PA does not stop them from happening. Active prevention and recognition of risks is what prevents injury and increases safety, and as such must be a key component of PA promotion. Injury prevention strategies will ensure that all can enjoy PA throughout their lifespans.