Time Course of Cardiac Arrhythmia Following High-Volume Exercise in Recreational Cyclists

The aim of this study was to investigate the time course of cardiac arrhythmias following a bout of high-volume exercise and to identify factors associated with abnormal cardiac arrhythmia.

Thirty-four recreational cyclists with 12 (interquartile range, 7-20) years of riding experience were recruited for this repeated-measure cohort study. Participants cycled for up to 6 hours at ≈80% heart rate reserve. Cardiac arrhythmias were recorded using a 5-lead Holter monitor for 4 days before exercise, the day of exercise, and 4 days after exercise. Arrhythmias were quantified as totals, abnormal arrhythmias (arrhythmias meeting international consensus criteria for cardiac arrhythmias requiring further investigation), and relative risk.

Sixty-eight percent of participants displayed abnormal cardiac arrhythmias. No between-day differences in the number of arrhythmias were found (P>0.10). However, the proportion of cyclists with abnormal ventricular arrhythmias was higher on the exercise day compared with preexercise days and the day after exercise (P<0.05). The relative risk of abnormal cardiac arrhythmia on the exercise day increased proportionally with the number of days that preexercise arrhythmias were recorded (peaking at a relative risk of 5.0 for those with arrhythmia on ≥3 preexercise days). Abnormal cardiac arrhythmia on the exercise day was associated with age, preexercise premature ventricular contractions, and preexercise abnormal cardiac arrhythmia.

High-volume cycling increased the likelihood of abnormal ventricular arrhythmia on the day of exercise. Extended monitoring revealed a high prevalence of abnormal cardiac arrhythmias among recreational cyclists. Current screening practices in many countries are typically limited to elite athletes, meaning recreationally active people are not routinely assessed for exercise-induced arrhythmias. Our findings suggest that some individuals in this group may have clinically relevant arrhythmias that would otherwise go undetected without targeted evaluation.