Relationship between carotid baroreflex sensitivity, physical fitness and activity in cyclists.

Carotid baroreceptors were stimulated with neck suction in 24 cycling tourists and pulse interval lengthening was measured. 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 s after the onset of the stimulus. The slope of this relationship was defined as baroreflex sensitivity. Baroreflex sensitivity averaged 7.3 +/- 0.8 ms/mmHg. The cycling tourists underwent an exercise test on a bicycle ergometer until exhaustion, and oxygen uptake, pulmonary ventilation, peak heart rate and exercise duration were determined. In single and multiple regression analysis, baroreflex sensitivity was not significantly related to basal heart rate, peak oxygen uptake and ventilation, duration of exercise or other training characteristics. The results suggest that in man the so-called 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.