Core body temperature correlates of transition from aerobic to anaerobic metabolism in running

• Published in: PeerJ (San Francisco, CA) Vol. 13; p. e19686
• Main Authors: Rakovac, Marija, Šentija, Davor, Maršić, Tošo, Babić, Vesna
• Format: Journal Article
• Language: English
• Published: United States PeerJ. Ltd 17.07.2025; PeerJ, Inc; PeerJ Inc
• Subjects: Acidosis; Adult; Anaerobic threshold; Anaerobic Threshold - physiology; Analysis; Anatomy and Physiology; Body temperature; Body Temperature - physiology; Breakpoints; Carbon dioxide; Correlation; Data exchange; Electromyography; Exercise intensity; Exercise Test; Exercise tests; Fitness equipment; Gas exchange; Heart rate; Humans; Hyperventilation; Hypotheses; Kinesiology; Male; Metabolism; Method comparison study; Physical activity; Physical fitness; Physiological aspects; Physiology; Rectal temperature; Reliability analysis; Reproducibility of Results; Running; Running - physiology; Segments; Sports Medicine; Statistical analysis; Thresholds; Treadmill running; Ventilatory threshold; Young Adult; Italy; Gas exchange; Method comparison study; Rectal temperature; Ventilatory threshold; Treadmill running
• ISSN: 2167-8359; 2167-8359; 2376-5992
• DOI: 10.7717/peerj.19686

We investigated core body temperature (CBT) during a graded exercise test (GXT) in comparison with gas exchange dynamics. Thirty-two active males performed a treadmill GXT (0.5 km/h increments every 30 seconds, 1.5% incline) until exhaustion. Gas exchange data and rectal temperature (T ) were continuously registered. Ten participants repeated the test for reliability assessment. The first and second gas exchange thresholds (VT and VT ) were determined by the simplified V-slope method, while CBT dynamics and eventual temperature thresholds (TT and TT ) were assessed according to the criteria defined in this study. Three independent evaluators determined gas exchange and temperature thresholds. In 29 subjects, T increase was best fitted with a 3-phase segmented model of successively steeper slopes, with a linear relationship in all three segments (17 subjects), or in two segments, with a quadratic relationship for the remaining segment (12 subjects). The between-segment intersection points were considered as TT and TT . In three participants, T was best fitted with a two-segment, single-breakpoint (TT or TT ) model. The evaluators' objectivity was satisfactory for VT (α = 0.786), very high for TT (α = 0.941) and VT (α = 0.948). TT and VT were moderately correlated (  = 0.41,  = 0.021) while VT and TT were highly correlated (  = 0.78,  < 0.001) showing a small, yet statistically significant difference (12.95 ± 1.9 vs 13.43 ± 1.7 km/h,  = 0.039). However, test-retest reliability was low. The breakpoints in CBT increase observed during graded running may represent transitions between the three intensity domains of physical activity.