ioral and Societal Sciences, Soesterberg, The Netherlands.

Heart-rate recovery (HRR) can be defined as the rate at which heart rate declines, usually within minutes after the cessation of physical exercise.1–3 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 activ-ity 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 charac-terized by parasympathetic reactivation and sympathetic withdrawal.3–7 Cardiac output is adjusted during exercise based on the metabolic demand. The regulation occurs by intrinsic autoregulation of cardiac pumping (the so-calle