Carotid baroreflex sensitivity and physical fitness in cycling tourists.

Carotid baroreceptors were stimulated with neck suction in 47 healthy subjects. Pulse interval lengthening was measured and the time course of the response was evaluated. Eight intensities of neck chamber suction were applied to select a criterion for computing the "RR response" that gives a significant linear relationship with the magnitude of the stimuli in the highest number of individuals. The best criterion was the maximal RR prolongation within 5 seconds after the onset of the stimulus. The slope of this relationship was defined as baroreflex sensitivity. The effect of physical fitness on baroreceptor function was investigated in 24 cycling tourists with a wide range of peak oxygen uptake and training characteristics. Baroreflex sensitivity averaged 7.3 +/- 0.8 msec X mm Hg-1 and was not significantly related to age, weight, basal heart rate, peak oxygen uptake and ventilation and other training characteristics. The results suggest that in man the so defined sensitivity of the carotid baroreflex control of heart rate is not influenced by the level of physical fitness and therefore the measurement of these characteristics can be neglected in evaluating baroreflex sensitivity.