A new technique to analyse threshold-intensities based on time dependent change-points in the ratio of minute ventilation and end-tidal partial pressure of carbon-dioxide production.

The aim of this study was to test the utility and effectiveness of an alternative computational approach to threshold-intensities based on time dependent change-points in minute ventilation divided by end-tidal partial pressure of CO (V/PCO) to reveal whether respiratory compensation point (RCP) is a third ventilatory threshold, or not. Ten recreationally active young adults and ten well-trained athletes volunteered to take part in this study. Following incremental ramp tests, gas exchange threshold (GET) and respiratory compensation point (RCP) were respectively evaluated by the slopes of VCO-VO and V-VCO using the Innocor system automatically. Respiratory threshold (RT) was analysed based on time dependent change-points in the V/PCO using binary segmentation algorithm. Additionally, those intersections were analysed independently by two experienced investigators using a visual identification technique in a double-blind design. According to the results, in the recreationally active group, there were the first (GET) and the second (GET) gas exchange thresholds which were identical with the RT (139 W; 1.9 L⋅min of VO; 1.73 L⋅min of VCO; 49.9 L⋅min of V versus 139 W; 1.88 L⋅min; 1.7 L⋅min; 49 L⋅min, respectively) and RT (186 W; 2.39 L⋅min of VO; 2.44 L⋅min of VCO; 66 L⋅min of V versus 187 W; 2.41 L⋅min; 2.49 L⋅min; 65.7 L⋅min, respectively). However, there were three threshold intensities which were determined by GET, GET, and RCP in well-trained athletes. Additionally, RT, RT, and RT were determined as valid surrogates of the GET (194 W; 2.56 L⋅min of VO; 1.99 L⋅min of VCO; 57.5 L⋅min of V versus 192 W; 2.61 L⋅min; 1.99 Lmin; 57.7 L⋅min, respectively), GET (267 W; 3.6 L⋅min of VO; 3.29 L⋅min of VCO; 94.5 L⋅min of V versus 266 W; 3.58 L⋅min; 3.26 L⋅min; 93.4 L⋅min, respectively), and RCP (324 W; 4.05 L⋅min of VO; 4.13 L⋅min of VCO; 124 L⋅min of V versus 322 W; 4.02 L⋅min; 4.07 L⋅min; 122 L⋅min, respectively) in well-trained athletes. There were high levels of agreements between the power outputs determined by traditional techniques and newly proposed change-points in RT. All markers were strongly correlated (p < 0.001). It was shown that RT technique can provide an accurate threshold determination. Furthermore, the RCP was observed as a third threshold-intensity for well-trained athletes but not for recreationally active young adults.