Passive thigh heating increases peak torque but does not attenuate declines in force production during repeated isokinetic knee extensor exercise in older adults.

Abstract

Aging is associated with declines in muscle function, leading to increased functional fatigability. Passive heating has demonstrated positive effects on muscle function during brief exercise in older adults, but the impact of heating on repeated contractions remains unknown. This study examined the effects of passive thigh heating on torque production during repeated and prolonged maximal dynamic isokinetic exercise. Fifteen healthy older adults (68 ± 8 years) completed a protocol involving 90 min of unilateral thigh heating (50°C) via a custom garment (HEAT), while the contralateral limb served as an unheated control (CONT). Participants performed 30 maximal isokinetic knee extensions at 180°/s before and after heating to assess peak torque during a single contraction, and average torque and total work done. Peak torque increased by 6 ± 7 N.m in HEAT (from 74 ± 33 N.m to 81 ± 33 N.m, +9%, p < 0.05), whereas CONT saw a no significant change (73 ± 31 N.m to 76 ± 28 N.m). Average torque declined significantly (p < 0.05), with decreases from the first third (68 ± 30 N.m) to the middle (57 ± 26 N.m) and final third of the fatigue task (51 ± 22 N.m). There was no difference in averaged torque thirds between HEAT and CONT highlighting that fatigue resistance was unaltered by the intervention. Total work done showed a non-significant 7% increase in HEAT (from 1619 ± 1100 J to 1751 ± 976 J, p = 0.273), a non-significant decrease of -4% was noted in CONT (from 1589 ± 790 J to 1528 ± 784 J p = 0.284). Passive heating enhanced peak torque production, but not fatigue resistance or work done during repetitive dynamic contractions in older adults indicating that the acute benefits of passive heating, may not extend to sustained or repetitive tasks.