Cardio-protective effects of endurance exercise

A report that appeared on the BBC news webpages on the 14th May 2014 suggested that lifelong endurance training could increase the risk of developing cardiac arrhythmia later in life ( The report is based on a paper published in Nature Communications in May 2014 ( advice, however, appears to contradict known cardio-protective effects of endurance exercise, writes Dr. Derek Ball of Heriot Watt University.


The Nature Communications report looked at the effects endurance training in rats or mice; either 12 weeks of interval training consisting of 60min/day, five days per week or two sessions per day of 60min of swimming every day for 4 weeks. The authors (D'Souza et al 2014) concluded that endurance training in the animals resulted in a reduction in resting heart rate (a normal response to endurance type training) and that the response was due to remodelling of the pacemaker cells of the heart rather than a change in the activity of the nerves that innervate the heart (the accepted explanation for a reduced resting heart rate). The authors concluded that these changes in resting heart rate were due to a direct effect on the pacemaker cells rather than any change in the way the nervous system can lower heart rate. Unlike the BBC headline, these authors did not report any abnormal changes in the rhythmicity of the heart - only that the resting heart of had lowered subsequent to training.


So where does the link to developing cardiac problems stem? In setting the scene for the paper D’Souza et al. (2014) suggest that the incidence of arrhythmia (an irregular heart beat) is more prevalent in older athletes than in an aged-matched cohort. The source of these data were taken from a cross-sectional study of former professional athletes (Cyclists that had participated in the Tour de Suisse) that were in their early-to-mid 60’s and were reported to have a higher incidence of atrial flutter and ventricular fibrillation than aged-matched controls (Baldesberger et al 2008 European Heart Journal). The rate of pacemaker treatment in the normal population of Switzerland is ~0.5% and, out of the cyclists, 2% had a pacemaker fitted – this seems to be an elevated proportion. However, not all of the reported abnormalities in the cyclists were confined to the pacemaker cells but other areas of the heart that too would require pacemaker insertion.


How should we view these findings in terms of advantages and disadvantages of continuing to exercise? A highly influential epidemiological study was published in the New England Journal of Medicine in 2002 by Myers and co-workers, their analysis of data collected in both a healthy cohort and patients with a history of cardiovascular disease quite clearly demonstrated that a low exercise capacity was associated with a greater mortality risk. In fact, the authors reported that a low aerobic capacity was the strongest predictor of risk of death in both cohorts. Exercise per se carries some risk and the studies by De’Souza et al (2014) and Baldesberger et al (2008) are by no means the only studies suggesting that prolonged participation in endurance exercise can be associated with a risk in terms of cardiac function. The benefits of exercise, however, far outweigh the risk in terms of overall metabolic and cardiovascular health and a sedentary lifestyle only increases mortality risk. Taken together, these epidemiology studies in mortality risk demonstrate that an enhanced aerobic capacity reduces mortality risk and the only way to improve or maintain your aerobic capacity is through exercise.