Heart-rate recovery (HRR) can be defined as the rate at which heart rate declines, usually within minutes after the cessation of physical exercise. [1][2][3] The autonomic nervous system (ANS) regulates both the initial increase in heart rate after the start of physical activity and the decrease in heart rate immediately after physical activity ends. The ANS is composed of a parasympathetic and a sympathetic branch that operate in a reciprocal and inverse manner: An increase in heart rate is caused by an increase in sympathetic activity combined with decreased parasympathetic drive, whereas HRR is characterized by parasympathetic reactivation and sympathetic withdrawal. [3][4][5][6][7] Cardiac output is adjusted during exercise based on the metabolic demand. The regulation occurs by intrinsic autoregulation of cardiac pumping (the so-called Frank-Starling law of the heart) and by sympathetic activation and parasympathetic deactivation, which increases heart rate and the contraction force of mainly the left ventricle. 8 Increased sympathetic activity combined with parasympathetic withdrawal (eg, during exercise) leads to reduced skin blood flow and increased blood flow to the muscles. 9 When the exercise stops, cardiac output is reduced by intrinsic autoregulation (by the ANS), more specifically by parasympathetic nervous system reactivation and inhibition of sympathetic impulses.Although it is well documented that changes in HRR coincide well with changes in training status in patient populations, 10 to our knowledge a systematic review on the use of HRR in athletes is missing. HRR may be an indicator of fitness, which is currently generally expressed in terms of VO 2max or VO 2peak , the maximum oxygen uptake during exhaustive exercise. Although VO 2max has a strong relationship with training status in a general population, it loses its predictive value for aerobic performance in already well-trained and elite athletes. 2 In addition, the typical error of measurement of VO 2max is relatively high, which makes VO 2max unreliable to monitor training changes over time. 2 In contrast, parameters such as HRR, peak power output, and/or peak treadmill running speed have lower typical errors of measurements, which makes them more sensitive to detect changes in training status.Therefore, the aim of this study was to conduct a systematic review on the use of HRR in athletes to track long-term changes in training status.
Methods
Data SourcesAn electronic literature search was performed in the digital databases of Scopus, EMBASE, and PubMed. The search terms used were a combination of heart/pulse rate(s), recovery/deceleration, (physical) exercise, and health(y) subjects/population. This search yielded 90 scientific articles (see Figure 1). Heart-rate recovery (HRR) has been proposed as a marker of autonomic function and training status in athletes. The authors performed a systematic review of studies that examined HRR after training. Five cross-sectional studies and 8 studies investigating changes over time (longitudinal)...