Passive thigh heating improves isokinetic but not isotonic muscle function.

PURPOSE: Optimal skeletal muscle function occurs when tissue temperature is elevated above resting. This study examined muscle torque production and maximal velocity responses to passive thigh heating on two occasions to determine the efficacy and reliability of the intervention.

METHODS: Twenty active, young participants (10 female) completed two identical visits whereby one thigh was wrapped in a water perfused garment circulating 50 °C water for 90 min; with the contralateral limb remaining unheated. Four maximal isokinetic repetitions were conducted at three speeds (slow, 60°/s; moderate, 180°/s; fast, 300°/s) followed by an isotonic set (25% MVIC) to assess muscle function on both limbs at baseline and every 30 min for 90 min. Muscle temperature (vastus lateralis) was assessed every 30 min.

RESULTS: Heating increased muscle temperature from baseline (32.2 ± 1.1 °C) to 30 min (36.8 ± 0.7 °C) with further 0.4 ± 1.3 °C increases in the following 30 min periods (p < .05). Heating increased peak torque during moderate (+10 ± 12 N m) and fast (+10 ± 11 N m) contractions from 30 min onwards relative to the unchanged control leg (p < .05). Peak torque during slow isokinetic and isotonic contractions were unchanged. Rate of force production and early force production increased in from baseline in the heated leg during the slow contractions by 14 % and 15 % respectively, whilst the control leg was unchanged throughout. Isokinetic and isotonic force muscle function was found to have excellent reliability across all contractile speeds (ICC>0.9) DISCUSSION: Passive heating of skeletal muscle improves peak torque production during moderate and fast isokinetic contractions and increases early force production in slow isokinetic contractions.