REF-1583 · Stadnyk et al., 2018 · Temperature · Paper · PubMed · Free full text

Heating one thigh above 38 °C during and for 20 min after each of 30 knee-extension sessions over 12 weeks showed no clear gain or loss in muscle or strength against the unheated thigh in 10 untrained young adults

Quadriceps lean mass rose 15% in both legs (difference p = 0.94), and torque, rate of torque development and 3-RM gains did not differ significantly; from the abstract

Main caveat: n = 10; one exercise; untrained people.
limited evidenceMeasured on non-athletes and recreational peopleRead from the abstract only

Stadnyk and colleagues tested whether warming the working muscle around each lifting session changes what the training builds, since heat can switch on protein-synthesis pathways. Ten healthy untrained young adults trained both legs separately on knee extension for 12 weeks.

One thigh, chosen at random, was warmed with an electric pad during each session and for 20 min afterwards, bringing muscle temperature above 38 °C; the other thigh trained unheated. Lean mass and strength rose by similar amounts in both legs, with no significant differences, and the authors report no clear positive or negative effect of the heating.

Participants

n = 10 (5 women), 21 ± 3 y, healthy, not resistance-trained.

Protocol

Training: 30 sessions over 12 weeks; 4 × 8 single-leg knee extensions at 70% of 1RM; loads progressed from strength tests every 4 weeks.
Heating (HOT leg): electric pad during and for 20 min after each session; muscle temperature >38 °C.
Control (CON leg): same training, no heat.
Outcomes: quadriceps lean mass (DXA), peak isokinetic torque at 90°/s, rate of torque development, 3-RM.

Key Results

OutcomeHeated legUnheated legBetween legs
Quadriceps lean mass+15 ± 7% (p = 0.00 as printed)+15 ± 6% (p = 0.00 as printed)p = 0.94 (authors: trivial)
Peak isokinetic torque, 90°/s+30 ± 25%+34 ± 33%p = 0.84
Rate of torque developmentabout +40%about +40%p = 0.73
3-RM+75 ± 16%+71 ± 14%p = 0.80
Changes in mass and strength did not differ between men and women.

Practical Application

Does heat around a lifting session help or hurt muscle gain? In 10 untrained young adults, keeping one working thigh above 38 °C during and 20 min after each of 30 sessions showed no clear difference in its growth or strength gain from the other leg — no sign of blunting and no sign of a bonus. This was local pad heating, not a sauna, in people new to lifting.
Inference, not tested here: with 10 people, a small effect in either direction cannot be ruled out, and beginners gaining 15% in 12 weeks may mask a small effect that trained lifters, gaining more slowly, would show.
The contrast in the base: cold water after strength training blunted gains in REF-011; this trial found no blunting from heat. Different temperatures, different trials, so it is not a head-to-head comparison.
Practice, not from this paper: the base's recovery guide does not list sauna or hot water after training as a recovery tool (SYNTH-70).

Limitations

n = 10; one exercise; untrained people.
Inference, not tested here: in a contralateral design both legs share the same blood and hormones, so any whole-body effect of heating one thigh would reach the control leg too.
Local heating only; core temperature and the number of people with any side effects are not given in the abstract.
Written from the abstract (the full text was not read).
How this entry was checked and changed
Why this level

a within-person comparison in 10 people, which the rubric treats like a crossover under 15 (B); the outcomes are DXA lean mass and strength, not markers, and the abstract gives the design and results in detail