Objective: To assess the association between exercise capacity and the risk of developing atrial fibrillation (AF).; Patients and Methods: A symptom-limited exercise tolerance test was conducted to assess exercise capacity in 5962 veterans (mean age, 56.8 +/- 11.0 years) from the Veterans Affairs Medical Center, Washington, DC. None had evidence of AF or ischemia at the time of or before undergoing their exercise tolerance test. We established 4 fitness categories based on age-stratified quartiles of peak metabolic equivalent task (MET) achieved: least fit (4.9 +/- 1.10 METs; n = 1446); moderately fit (6.7 +/- 1.0 METs; n = 1490); fit (7.9 +/- 1.0 METs; n = 1585), and highly fit (9.3 +/- 1.2 METs; n = 1441). Multivariable Cox proportional hazards regression models were used to compare the AF-exercise capacity association between fitness categories.; Results: During a median follow-up period of 8.3 years, 722 (12.1%) individuals developed AF (14.5 per 1000 person-years; 95% CI, 13.9-15.9 per 1000 person-years). Exercise capacity was inversely related to AF incidence. The risk was 21% lower (hazard ratio, 0.79; 95% CI, 0.76-0.82) for each 1-MET increase in exercise capacity. Compared with the least fit individuals, hazard ratios were 0.80 (95% CI, 0.67-0.97) for moderately fit individuals, 0.55 (95% CI, 0.45-0.68) for fit individuals, and 0.37 (95% CI, 0.29-0.47) for highly fit individuals. Similar trends were observed in those younger than 65 years and those 65 years or older.; Conclusion: Increased fitness is inversely and independently associated with the reduced risk of developing AF. The decrease in risk was graded and precipitous with only modest increases in exercise capacity. These findings counter previous suggestions that even moderate increases in physical activity, as recommended by national and international guidelines, increase the risk of AF, with marked protection against AF noted with increasing levels of fitness. (C) 2016 Mayo Foundation for Medical Education and Research
