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

PURPOSE

We investigated core body temperature (CBT) during a graded exercise test (GXT) in comparison with gas exchange dynamics.

METHODS

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.

RESULTS

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.

CONCLUSION

The breakpoints in CBT increase observed during graded running may represent transitions between the three intensity domains of physical activity.