Changes in calf skin temperature during ramp-incremental cycling exercise and their association with gas exchange and...

Objective.We tested the hypothesis that the oxygen uptake (O₂) associated with systematic changes in skin temperature (T_sk) during ramp-incremental exercise would coincide with the respiratory compensation point (RCP) and not the gas exchange threshold (GET).Approach.Thirty-eight healthy adults (16 females; 24 ± 5 years, body mass 73.0 ± 11.4 kg, height 174.8 ± 8.5 cm) completed a ramp-incremental exercise test on a cycle ergometer (20-45 W min^-1depending on self-reported aerobic fitness; selected to induce task disengagement within 10-15 min) in a climate-controlled laboratory. Throughout the protocol, ventilatory and gas exchange variables were acquired breath-by-breath using a metabolic cart andT_skof the posterior calf was recorded revolution-by-revolution using an infrared camera.Main results.TheT_sk-time relationship exhibited either an abrupt or gradual deceleration as exercise time progressed. TheO₂associated with this change-point was identified visually or by finding the local maximum of the second derivative of a 6th-order polynomial fit to the data. TheO₂at GET and RCP were determined visually. Overall, theO₂at GET, RCP andT_skbreakpoint identified visually or modelled were 1884 ± 466, 2633 ± 747, 1969 ± 462, and 1769 ± 508 ml∙min^-1, respectively. Compared to theO₂at GET, higher values were reported whenT_skbreakpoint was identified visually (p= 0.04, ESg = 0.3, 95%CI[1, 170 ml min^-1]) and lower by the second derivative (p< 0.01, ESg = 0.4, 95%CI[30, 199 ml min^-1]). Larger effect sizes were observed for RCP (visually:p< 0.001, ESg = 1.3, 95%CI[524, 803 ml min^-1]; second derivative:p< 0.001, ESg = 1.7, 95%CI[724, 1003 ml min^-1]). Intraclass correlation ofO₂betweenT_skand GET ranged from very good-to-excellent (0.67-0.92) but were not significant for RCP. For GET, mean absolute percentage error was 12.5% (95%CI: 9.4%-15.7%) and 14.5% (95%CI: 11.1%-17.9%) for the visual and second-derivative methods, respectively, and for RCP, 23.2% (95% CI: 18.6%-27.8%) and 31.4% (95% CI: 26.7%-36.2%).Significance.Findings suggest a statistical association between intensity-dependent changes in metabolism and theT_skresponse of the calf.