Balancing Exercise Benefits Against Heartbeat Consumption in Elite Cyclists

Abstract

T he cardiovascular system demonstrates remarkable efficacy in responding to the increased metabolic demand during exercise. However, uncertainty persists regarding the potential health implications of more extreme volumes of intense exercise training. 1 Colloquially, the assertion regarding the potential harms of exercise has been trivialized by the statement that we have a fixed number of heartbeats over a lifetime and that exercise might deplete this. This is based on the observation that, across mammalian species, life span is predetermined by the basic energetics of living cells, heart rate serves as a marker of metabolic rate, and that life expectancy is inversely proportional to the heart rate. 2 This concept resonates with the well-established fact that an increased resting heart rate is associated with cardiovascular risk. 3 However, regular exercise also reduces the resting heart rate long-term, likely offsetting a transient exertional heart rate increase. 3 Thus, we are left with balancing the equation between increased heart rates throughout exercise and the lower resting heart rates observed in habitual exercisers. As an exploratory analysis, we aimed to investigate the relationship between exercise training and an average 24-hour heart rate. We examined the average heart rate on 24h-Holter monitoring in 109 athletes and 38 healthy controls using the full Australian cohort of the Prospective Athletic Heart (Pro@Heart) study, which has been described in full previously. 4 Although the Pro@Heart study includes both Belgian and Australian participants, only the Australian cohort was included in this analysis due to the use of a different Holter monitoring device in Belgium and the unavailability of some required data. The study protocol was approved by the Human Research Ethics Committee at each recruiting site. All participants were encouraged to perform their normal activities and exercise training while wearing the Holter monitor which recorded heart rhythm, rate, and an accelerometer-derived estimate of activity time. The athletes were slightly younger than controls (median 19 [17-22] vs 21 [19-22] years; P = 0.001), sex ratio was similar (69.6% male vs What is the clinical question being addressed? What is the relationship between lower resting heart rates and exertional increases in athletes? What is the main finding? The concept of "heartbeat consumption" is introduced as a straightforward metric that may offer insights on training load and the possible adverse effects of intense exercise.