Localized and systemic variations in central motor drive at different local skin and muscle temperatures

This study investigated the ability to sustain quadriceps central motor drive while subjected to localized heat and metaboreceptive feedback from the contralateral leg. Eight active males each completed two counter-balanced trials, in which muscle temperature (T_m) of a single-leg (TEMP-LEG) was altered to 29.4 (COOL) or 37.6°C (WARM), while the contralateral leg (CL-LEG) remained thermoneutral; 35.3 and 35.2°C T_m in COOL and WARM respectively. To activate metaboreceptive feedback, participants first performed one 120-s isometric maximal voluntary contraction (MVC) of the knee extensors in the TEMP-LEG, immediately followed by post-exercise muscle ischemia (PEMI) via femoral blood flow occlusion. To assess central motor drive of a remote muscle group immediately following PEMI, another 120-s MVC was subsequently performed in the CL-LEG. Voluntary muscle activation (VA) was assessed using the twitch interpolation method. Perceived mental effort and limb discomfort were also recorded. In a cooled muscle, a significant increase in mean force output and mean VA (force, p<0.001; VA, p<0.05) as well as a significant decrease in limb discomfort (p<0.05) occurred during the sustained MVC in the TEMP-LEG. However, no differences between T_m were observed in mean force output, mean VA or limb discomfort during the sustained MVC in the CL-LEG (Force, p=0.33; VA, p>0.68, limb discomfort, p=0.73). The present findings suggest that elevated local T_sk and T_m can increase limb discomfort and decrease central motor drive, but this does not limit systemic motor activation of a thermoneutral muscle group.

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