The Effect of a Secret Manipulation of Ambient Temperature on Heat Storage and Voluntary Exercise Intensity

Abstract

The Central Governor Model (CGM) suggests that physiological afferents, such as changes in ambient temperature or perturbations in the rate of heat storage (HS), are centrally integrated in a dynamic feed-forward manner, with the end goal of regulating voluntary exercise intensity in order to maintain physiological homeostasis. One limitation of previous research into this model is that subjects have been aware of the existence of an environmental manipulation. Because of this, a placebo effect may have influenced the anticipatory planning before the start of exercise, making it difficult to isolate the dynamic integration during exercise itself. PURPOSE: To directly test the CGM by secretly manipulating ambient temperature (Tam) while cycling at a set rate of perceived exertion (RPE). METHODS: Using a single trial to remove between-trial variability, participants cycled at a constant RPE of 14 while Tam was manipulated in an A-B-A pattern at 20-minute intervals from 20°C to 35°C, then returned to 20°C. Participants were deceived, both to the true purpose of the study and the Tam manipulation, to elicit dynamic pacing strategies without conscious anticipation. Power output was measured continuously throughout each trial and its synchronicity with changes in HS and Tam were quantified using Auto-Regressive Integrated Moving Averages (ARIMA) analysis. Furthermore, blood lactate measurements were taken and A-B-A differences were analyzed using repeated measures ANOVA. RESULTS: Ten recreational to competitive cyclists (mean±SD, age: 35.1±13.5 y, mass: 72.5±15.9 kg, height: 174.9±9.1 cm, body fat: 11.2±5.6%, VO2peak 57.6±6.3 mL/kg/min, and peak power output: 332±53 W) participated. Exercise intensity decreased during the 35°C manipulation in all subjects and ARIMA analysis indicates that power output is significantly correlated to changes HS (r2 = 0.984, Ljung-Box statistic = 0.083). There were no significant differences in blood lactate concentration throughout each trial (p = 0.164) despite changes in Tam. CONCLUSIONS: Real time dynamic sensation of Tam and integration of HS directly influences voluntary pacing strategies during sub-maximal cycling at a constant RPE while non-significant changes in blood lactate suggest an absence of peripheral fatigue. Supported by NSERC Discovery 227912-2007.