Whether sports participation is healthy or detrimental for the individual is a matter of dosage

That regular strenuous physical exercise is an excellent, effective and ‘cheap’ method in the primary and secondary prevention of cardiovascular disease has been well established. Even in the presence of cardiovascular risk factors and/or cardiovascular disease with or without atrial fibrillation, regular physical exercise improves the health and diminishes the burden of arrhythmias in the individual. Early studies proving this concept mainly involved the male part of the population, later the positive effect was also confirmed in preand post-menopausal females. There is, however, much discussion regarding the optimal level (frequency, duration and intensity) of exercise for maximal beneficial effect. Study results show that the higher the level of aerobic physical activity, the better the decrease in cardiovascular risk profile, in male and female athletes. The aerobic physical activity was expressed in specific time slots per week (7h per week spread over several days) or METS (metabolic equivalent (MET) is amount of oxygen consumed per kg body weight per minute; in rest +3.5ml O2) to determine the level that would effectively reduce cardiovascular risk, including arrhythmias such as atrial fibrillation [1, 2]. In the last decade, more vigorous exercise has become ‘fashionable’. Marathon runs are very popular and obstacle races in extreme conditions (wet, ice, mud) have gained in popularity. For 2018, nearly 3,500 races are scheduled worldwide in the ‘ultra’ running category, clearly exceeding the marathon distance. Whether this extreme physical load could cause