Effect of environmental temperature change on the neuromechanical function of the quadriceps muscles

This study compared neuromechanical characteristics of voluntary (maximum voluntary contraction (MVC) peak torque, rate of torque development (RTD), voluntary activation (VA)) and electrically stimulated contractions (peak torque, RTD) when performed under the same temperature conditions. Twelve physically active males performed two isometric MVCs of the knee extensors in an isokinetic dynamometer. The MVCs were performed after lower limb submersion for 20 min in hot (40 degrees C) or cold (10 degrees C) water. A control MVC was performed in ambient room temperature (17 +/- 0.7 degrees C). Electrical twitches were delivered at rest pre-MVC (Unpotentiated), during the plateau phase of the MVC (Superimposed) and post-MVC (Potentiated). Peak torque for MVC, Unpotentiated and Potentiated was recorded. RTD was calculated for the MVC (at 50, 100, 150, 200 ms and peak torque time points), Unpotentiated and Potentiated twitches, while muscle activation capacity (using the central activation ratio method) was calculated. There was no significant change between conditions in MVC peak torque, MVC RTD, muscle activation capacity and (averaged) twitch peak torque (p > 0.05). Twitch RTD for the hot condition (1025.0 +/- 163.0 N.m.s(-1)) was significantly higher (p = 0.003) than control (872.3 +/- 142.9 N.m.s(-1)). In conclusion, environmental temperature changes, in the range examined, do not affect the ability to generate maximum torque or any of the RTD parameters in maximum voluntary isometric contractions. In contrast, increased heat results in higher RTD in electrically stimulated contractions, most likely induced by reduced contraction time. This has practical implications for the use electromyostimulation tools for injury prevention.