Global and national public health authorities recommend that adults take part in 150 min of moderate to vigorous physical activity (MVPA) each week. The epidemiological literature strongly supports the beneficial associations of the total amount of MVPA with health outcomes. Several systematic reviews and meta-analyses have summarised the evidence for the association between MVPA and the risk of disease-specific and all-cause mortality. For example, one meta-analysis found that insufficient MVPA (defined as not meeting the current World Health Organization (WHO) guidelines for MVPA1) is associated with a 28% higher risk of all-cause mortality, compared with sufficient MVPA. Considering the high levels of physical inactivity globally, Lee and colleagues estimated that more than 5 million premature deaths a year would be prevented if physically inactive people became sufficiently active. Considerable interest has also been shown in the effects of different types of physical activity (eg, walking, cycling, running, swimming) on health and risk of premature mortality. In other words, for a given amount of MVPA, does the type of physical activity matter?
Running is among the most popular types of physical activity. It has been estimated that each month around 3.7 million (8.5%) English adults take part in running as a sport or recreational activity. Other countries, such as Australia and the USA, also have high participation rates. The 2017 Physical Activity Council’s survey ranked running in the top 10 preferred activities in which inactive 25–44-year-old US adults wished to take part. Given its popularity, running has great potential for improving population health. The Royal College of General Practitioners (RCGP) has acknowledged this potential by partnering with the parkrun UK initiative, to promote the uptake of running and walking among general practitioners and their patients.
In a systematic review, Oja et al17 concluded that the evidence for health benefits is scarce for participation in all sports except for running and football. The authors concluded that there is
(i) moderate evidence for the associations between running and improved aerobic fitness, cardiovascular function and running performance.
(ii) limited evidence for associations of running with improvements in metabolic fitness, adiposity status and postural balance.
(iii) inconclusive evidence for the associations of running with cardiac adaptation, muscular strength and disease-specific and all-cause mortality.
Oja et al17 identified only one study on running participation and the risk of mortality. A subsequent, comprehensive narrative review summarised the evidence for the association of running and a range of health outcomes, including major cardiometabolic outcomes, bone and respiratory health, disability and disease-specific and all-cause mortality. The strength of the association between running participation and the risk of all-cause and disease-specific mortality varied across different studies. To date, no meta-analysis has synthesised evidence on the association between running participation and the risk of mortality.
To enable evidence-based prescribing of running as a health-enhancing physical activity, it is crucial to identify its optimal dose. The 'dose' of running is usually defined by its frequency (eg, two times a week), overall duration in a given period (eg, 40 min/week), pace (eg, 10 km/h) and the total volume (eg, expressed as the product of the overall weekly duration of running and the metabolic equivalent (MET) of running at a given pace; 800 MET-min/week). It might be expected that higher running doses would lead to better health outcomes, such as improved physical and metabolic fitness. However, contrary to this assumption, Schnohr et al31 suggested there may be a U-shaped relationship between the dose of running and the risk of all-cause mortality. Compared with ‘sedentary’ non-runners, those who ran <2.5 hours a week, those who ran less than four times a week and those who ran at a slow or average pace had significantly lower risks of all-cause mortality.31 No statistically significant adjusted hazard ratios (HRs) were found for those who ran ≥2.5 hours a week, those who ran four or more times a week and those who ran at a fast pace.31 The U-shaped relationship may be explained by possible pathological changes in cardiovascular tissues induced by extreme doses of endurance sports over a long term—for example, the development of patchy myocardial fibrosis, creating a substrate for heart arrhythmias. However, a relatively small number of participants in the study of Schnohr et al31 were classified as “strenuous” runners and only a few deaths were registered in this group, limiting the statistical power of the analysis. The finding has sparked much discussion among researchers. To date, the available evidence on the dose–response relationship between running and the risk of mortality has not been synthesised in a meta-analysis.
The aim of this systematic review and meta-analysis was, therefore, to synthesise available evidence on the association of running participation and the dose of running with the risk of all-cause, cardiovascular and cancer mortality.