Can You Get Too Much Exercise ?
Circulation has just published an article by Svedberg and colleagues examining the incidence of Afib in particpants in the Vasaloppet x-country ski races. I wrote a commentary for PracticeUpdate published on Sept 5, 2018. PracticeUpdate is a great (& free) way to stay up with the latest in cardiology. I occasionally write on exercise and heart disease and on cardiac prevention for them. Here is my summary of the Svedberg article, which is released electronically, but not yet in print.
The practice of endurance exercise and exercise training has been linked to a higher incidence of atrial fibrillation (AF). Svedberg and colleagues used results from the Vasaloppet ski races from 1989 to 2011 to examine the incidence of AF in Swedish participants. The races ranged from 30 to 90 km (18.6 to 55.8 miles) in distance. Swedish national databases were used to determine the date of AF diagnosis, use of oral anticoagulants, income and education level, CHA2DS2-VAS score, and death. Performance was divided into five groups based on the individual’s best finishing time, calculated as a percentage of the winning time. Percentage of the winning time helped adjust for differences in race length and weather conditions that could have affected performance. Performances among skiers were separated into those performing in the 5th, 35th, 50th, 65th, and 95th percentile. A total of 208,654 skiers were matched with 524,448 non-skiers from national registries, and the risk of AF, stroke, and death were compared between skiers and non-skiers and among the skiers.
Skiers were, on average, 5 years younger than non-skiers at study entry and had higher education levels, higher income, and fewer concomitant diseases. Consequently, the analysis included adjustments as appropriate for age, socio-economic status, diseases associated with AF, and age at study inclusion.
A total of 1.2% of the skiers and 1.7% of the non-skiers were diagnosed with AF over the duration of the study. Strokes occurred in 0.3% of the skiers and 1.4% of non-skiers. Death occurred in 1.2% of skiers and 3.9% of non-skiers. In skiers with AF, 8.3% had a stroke and 10.7% died. In non-skiers with AF, 9.7% had a stroke and 20.3% died.
Skiers were 1.8 years younger than non-skiers when diagnosed with AF. Skiers had lower CHA2DS2-VASc scores at diagnosis (0.96 vs 1.38) and therefore a lower indication for anticoagulation by European guidelines (49.7% vs 63.1%), but more skiers actually received oral anticoagulants (58.0% vs 52.3%).
Female skiers had a lower incidence of AF than non-skiers. The incidence of AF in male skiers was not different from that in non-skiers in unadjusted data; but, after adjustment for conditions associated with AF, the incidence was higher in the male skiers. Furthermore, among male skiers, the incidence of AF was higher in those completing the most races and in those with the best performance times, probably representing what the authors call the “training load.” Both male and female skiers had lower rates of stroke compared with non-skiers. The stroke incidence was highest among non-skiers with AF, but the incidence of stroke was higher in skiers with AF than in skiers and non-skiers without AF. Skiers with AF had half the mortality rate of non-skiers with AF.
The strength of this study is its enormous sample size, but there are weaknesses, including an inability to match skiers and non-skiers on AF risk factors and absence of information on diet, tobacco, and alcohol use. The outpatient data included visits to emergency departments and to specialists, but did not include primary care visits and could have missed AF episodes not referred to cardiologists. There were no data on physical activity among the non-skiers, and few women participants in the 90 km Vasaloppet race, so there are less data on high training loads in women.
Despite these limitations, the large sample size and the thoroughness of the analysis add to the suspicion that large amounts of endurance exercise can increase the incidence of AF and that AF in endurance athletes is not benign.
