Passive thigh heating increases peak torque but does not attenuate declines in force production during repeated isokinetic knee extensor exercise in older adults.
Passive thigh 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.
Key Findings
Results
Passive thigh heating significantly increased peak torque in the heated limb of older adults.
Fifteen healthy older adults (68 ± 8 years) completed 90 minutes of unilateral thigh heating at 50°C via a custom garment.
Peak torque increased by 6 ± 7 N.m in HEAT (from 74 ± 33 N.m to 81 ± 33 N.m, +9%, p < 0.05).
The contralateral unheated control (CONT) limb showed no significant change in peak torque (73 ± 31 N.m to 76 ± 28 N.m).
Peak torque was assessed during a single maximal isokinetic knee extension at 180°/s before and after the heating protocol.
Results
Passive thigh heating did not attenuate fatigue-related declines in average torque during 30 repeated maximal isokinetic knee extensions.
Average torque declined significantly across the 30-repetition fatigue task (p < 0.05).
Average torque decreased from the first third (68 ± 30 N.m) to the middle third (57 ± 26 N.m) and to the final third (51 ± 22 N.m).
There was no difference in averaged torque thirds between HEAT and CONT, indicating that fatigue resistance was unaltered by the intervention.
The exercise protocol involved 30 maximal isokinetic knee extensions at 180°/s.
Results
Total work done during the repeated isokinetic exercise task was not significantly altered by passive heating.
HEAT showed a non-significant 7% increase in total work done (from 1619 ± 1100 J to 1751 ± 976 J, p = 0.273).
CONT showed a non-significant decrease of -4% (from 1589 ± 790 J to 1528 ± 784 J, p = 0.284).
Neither the heated nor the control limb demonstrated statistically significant changes in total work done.
Background
Aging is associated with declines in muscle function leading to increased functional fatigability, providing the rationale for investigating passive heating as an intervention.
Passive heating has demonstrated positive effects on muscle function during brief exercise in older adults.
The impact of heating on repeated contractions was previously unknown prior to this study.
The study used a within-subject design with the contralateral limb serving as an unheated control to isolate heating effects.
Conclusions
The acute performance benefits of passive thigh heating do not appear to extend to sustained or repetitive dynamic exercise tasks in older adults.
While peak torque (a single-contraction measure) improved with heating, neither average torque across repetitions nor total work done showed significant improvement.
The authors concluded that 'the acute benefits of passive heating may not extend to sustained or repetitive tasks.'
The study involved 15 healthy older adults, which represents a relatively small sample size.
The heating protocol was 90 minutes of unilateral thigh heating at 50°C.
What This Means
This research suggests that heating the thighs using a warm garment (at 50°C for 90 minutes) can temporarily boost the peak force that older adults can produce during a single knee extension exercise. In a study of 15 older adults (average age 68), the heated leg showed about a 9% increase in peak torque after heating, while the unheated leg showed no significant change. This finding adds to earlier evidence that warming muscles before exercise may offer short-term strength benefits for older people.
However, when participants performed 30 repeated maximal knee extensions to simulate a more sustained exercise task, the heated leg showed the same pattern of fatigue as the unheated leg — force dropped significantly from the start to the end of the set, and there was no meaningful difference in how much total work was done between heated and unheated limbs. This suggests that while passive heating can sharpen the initial peak of muscle performance, it does not help muscles resist fatigue during prolonged or repeated efforts.
This research matters because muscle weakness and fatigue are common concerns for older adults and can affect everyday activities like climbing stairs or rising from a chair. The findings suggest that passive heating strategies might be useful as a warm-up to briefly enhance maximal muscle output, but they are unlikely to help older adults sustain performance over the course of a longer activity. Future research may need to explore other approaches, or different heating methods, to address fatigue resistance in aging muscles.
Denny D, Low D, Gibson O. (2026). Passive thigh heating increases peak torque but does not attenuate declines in force production during repeated isokinetic knee extensor exercise in older adults.. Physiological reports. https://doi.org/10.14814/phy2.71105