Abstract

Objective: To test whether ventilatory thresholds, measured during an exercise test, could be assessed using time varying analysis of respiratory sinus arrhythmia frequency (f_RSA).

Methods: Fourteen sedentary subjects and 12 endurance athletes performed a graded and maximal exercise test on a cycle ergometer: initial load 75 W (sedentary subjects) and 150 W (athletes), increments 37.5 W/2 min. f_RSA was extracted from heart period series using an evolutive model. First (T_V1) and second (T_V2) ventilatory thresholds were determined from the time course curves of ventilation and ventilatory equivalents for O₂ and CO₂.

Results:f_RSA was accurately extracted from all recordings and positively correlated to respiratory frequency (r = 0.96 (0.03), p<0.01). In 21 of the 26 subjects, two successive non-linear increases were determined in f_RSA, defining the first (T_RSA1) and second (T_RSA2) f_RSA thresholds. When expressed as a function of power, T_RSA1 and T_RSA2 were not significantly different from and closely linked to T_V1 (r = 0.99, p<0.001) and T_V2 (r = 0.99, p<0.001), respectively. In the five remaining subjects, only one non-linear increase was observed close to T_V2. Significant differences (p<0.04) were found between athlete and sedentary groups when T_RSA1 and T_RSA2 were expressed in terms of absolute and relative power and percentage of maximal aerobic power. In the sedentary group, T_RSA1 and T_RSA2 were 150.3 (18.7) W and 198.3 (28.8) W, respectively, whereas in the athlete group T_RSA1 and T_RSA2 were 247.3 (32.8) W and 316.0 (28.8) W, respectively.

Conclusions: Dynamic analysis of f_RSA provides a useful tool for identifying ventilatory thresholds during graded and maximal exercise test in sedentary subjects and athletes.