Using Thorax Expansion to Detect a Ventilatory Inflection Point in the Field

Assessing an individual's physical fitness can usually be achieved through evaluating lactate or ventilatory thresholds. Unfortunately, the detection of ventilatory thresholds still requires uncomfortable mass flow sensors and a laboratory setting. Therefore, this study aimed to evaluate a ventilatory inflection point (VIP) derived from thorax expansion as a useful surrogate to assess an individual's physical fitness under field conditions. 348 and 107 ramp tests have been selected respectively to examine validity and retest variability of VIP. The individual anaerobic threshold (IAT) determined by means of blood lactate sampling was used as reliable rationale for evaluation. Calibrated respiratory inductance plethysmography (RIP) was utilized to derive ventilation from thorax expansion during the ramp test. An automated software routine was applied to detect the VIP. Speed, heart rate and ventilation at the VIP correlated significantly to corresponding values at IAT (r=0.840, 0.876, 0.933). Non-systematic differences between repeated testing ranged within ±1.15 km·h(-1), ±8.74 b·min(-1) and ±12.69 l·min(-1) (±1.96 SD). The timing of VIP is not solely dependent on the aerobic capacity and might instead quantify an individual's physical fitness in terms of the efficiency of the compensative and supportive ventilatory response during increased exercise intensities.