BACKGROUND: Physical fitness is known to influence arterial stiffness. Resting heart rate is reduced by exercise and positively associated with arterial stiffness. This study aimed to investigate the role of resting heart rate in the relationship of physical fitness with arterial stiffness. METHODS: Subjects were 2,328 young adults from the Childhood Determinants of Adult Health study. Cardiorespiratory fitness was estimated as physical work capacity at a heart rate of 170 bpm. Muscular strength was estimated by hand-grip (both sides), shoulder (pull and push), and leg strength. Arterial stiffness was measured using carotid ultrasound. RESULTS: Arterial stiffness was negatively associated with cardiorespiratory fitness (men P < 0.001; women P = 0.002), and positively associated with muscular strength in women (P = 0.002) but not in men. Resting heart rate was positively associated with arterial stiffness (P < 0.001 both men and women). Adjustment for resting heart rate reduced the inverse association of arterial stiffness with cardiorespiratory fitness by 93.7% (men) and 67.6% (women) but substantially increased the positive association of arterial stiffness with muscular strength among women and revealed a positive association of arterial stiffness with muscular strength among men. These findings were independent of body size, blood pressure, biochemical markers, socioeconomic status, smoking, and alcohol consumption. CONCLUSIONS: Our findings attribute a key intermediary role for resting heart rate in the relationship between fitness and arterial stiffness, whereby higher cardiorespiratory fitness may reduce arterial stiffness mainly through resting heart rate, and higher muscular strength might have deleterious effects on arterial stiffness that are partially offset by lower resting heart rate.
