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

Authors

Jose Ignacio Priego Quesada, Nathan Mackay, Dami Adejuwon, Daniel Keir

Published in

Physiological measurement. Jul 13, 2026. Epub Jul 13, 2026.

Abstract

We tested the hypothesis that the oxygen uptake (V̇O2) associated with systematic changes in skin temperature (Tsk) during ramp-incremental exercise would coincide with the respiratory compensation point (RCP) and not the gas exchange threshold (GET).
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 depending on self-reported aerobic fitness; selected to induce task disengagement within 10-15 minutes) in a climate-controlled laboratory. Throughout the protocol, ventilatory and gas exchange variables were acquired breath-by-breath using a metabolic cart and Tsk of the posterior calf was recorded revolution-by-revolution using an infrared camera.
The Tsk-time relationship exhibited either an abrupt or gradual deceleration as exercise time progressed. The V̇O2 associated 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. The V̇O2 at GET and RCP were determined visually. Overall, the V̇O2 at GET, RCP and Tsk breakpoint identified visually or modelled were 1884±466, 2633±747, 1969±462, and 1769±508 mL∙min-1, respectively. Compared to the V̇O2 at GET, higher values were reported when Tsk breakpoint was identified visually (p=0.04, ESg=0.3, 95%CI[1, 170 ml/min]) and lower by the second derivative (p<0.01, ESg=0.4, 95%CI[30, 199 ml/min]). Larger effect sizes were observed for RCP (visually: p<0.001, ESg=1.3, 95%CI[524, 803 ml/min]; second derivative: p<0.001, ESg=1.7, 95%CI[724, 1003 ml/min]). Intraclass correlation of V̇O2 between Tsk and 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%).
Findings suggest a statistical association between intensity-dependent changes in metabolism and the Tsk response of the calf.

PMID:
42443136
Bibliographic data and abstract were imported from PubMed on 14 Jul 2026.

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