V˙O2 linear-onset kinetics spanning steady- and non-steady-state exercise

Introduction The traditional method for quantifying the kinetics of the increase in the body’s consumption of oxygen ( V˙ O 2 ) during exercise transitions to steady state involves application of a mono-exponential function. Anomalies exist to question the validity of this method, as they show the initial (∼1 min) of this V˙ O 2 response is linear. Methods Fourteen highly endurance trained subjects (12 males, 2 females) completed a ramp incremental cycling protocol, as well as 8 different constant load trials at 43 to 148 % of their critical power (CP). Results For the initial five exercise bouts, the linear fit of the initial segment was significantly more accurate (lower standard error of estimates; SE) compared to the mono-exponential fit (p < 0.001). There were two different systematic profiles of the linear onset (LO) V˙ O 2 slope from different bouts of increasing exercise intensities; 1) a sustained increase (increased kinetics) (n = 7), and 2) a plateau or decrease (impaired kinetics) (n = 7). Both sub-groups were similar in all measures of cardio-respiratory and muscular endurance. Discussion The LO V˙ O 2 kinetics method is superior to the traditional approach as it was a more valid representation of the initial V˙ O 2 response, can be applied to both steady and non-steady state exercise intensities, requires less than 2 min of exercise, but across multiple bouts, and identifies more complex physiology than the mono-exponential method. Added research is needed to discern the most valid methods to measure LO V˙ O 2 kinetics, and to learn more about its physiological determinants compared to the traditional mono-exponential method.