REF-1582 · Ahokas et al., 2025 · Frontiers in Sports and Active Living · Paper · PubMed · Free full text
In 36 female team-sport athletes (18 per group analysed) on a 6-week strength-and-power block, 10 min of mild infrared sauna after training three times a week did not change muscle growth against no sauna (thigh cross-sectional area grew in both groups, with no group-by-time interaction for any hypertrophy measure), while one loaded jump improved only in the sauna group; the groups were pair-matched, not randomised, and the cabin was set to 50 °C but measured about 31 °C at hip height
Main caveat: Not randomised: pairs were matched on team, performance and age, and how each pair was split is not described; the loaded-jump baseline differed between groups.
Ahokas and colleagues asked whether a regular infrared sauna after training adds to the gains of a strength programme.
Forty female team-sport athletes were matched in pairs and split into a sauna group and a control group of 20 each; 36 were analysed (two dropped out, one used a traditional sauna and hot-water immersion in her free time against instructions, and the partner of one drop-out was removed).
Both groups did 6 weeks of strength and power training two or three times a week; the sauna group also sat 10 min in an infrared cabin after training three times a week. Training raised vastus lateralis cross-sectional area and lower-body lean mass in both groups, and no hypertrophy measure showed a group-by-time interaction.
A countermovement jump with 15% of body mass added improved in height and peak power only in the sauna group (interaction p = 0.002 and p = 0.010), and the 5-m sprint split showed an interaction without significant post hoc differences.
The authors conclude that the sauna did not significantly affect hypertrophy and might help power, call the positive effects minor or unclear, and write that their data give no reason to expect a brief infrared sauna to impair adaptation.
Participants
n = 40 enrolled (20 sauna, 20 control); 36 analysed (18 and 18).
At enrolment: sauna group 22 ± 5 y, 167 ± 7 cm, 69.4 ± 18.2 kg; control group 23 ± 5 y, 168 ± 6 cm, 69.5 ± 13.7 kg. Basketball 14, futsal 18, ice hockey 4, American football 4; some under 18 (guardian consent).
Earlier sauna habits ranged from none in six months (3) to 2-5 times a week (6); one had used an infrared cabin once.
Hormonal status (diaries): 23 naturally menstruating (4 of them amenorrhoeic or oligomenorrhoeic), 7 on combined and 5 on progestin-only contraception; 5 did not return the diary.
Protocol
Training: 2 sessions a week (two teams, n = 10) or 3 (four teams, n = 30), each pairing a resistance exercise with an explosive one (for example squats with box jumps, hip thrusts with resisted 10-m sprints), 2 min rest. Weeks 1-2: 3 sets at 70-80% 1RM; weeks 3-4: 4 sets at 80-85%; weeks 5-6: 3 sets at 50-55%; mostly 4-6 reps, moved fast, guided by reps in reserve, not near failure. Team practice otherwise as usual.
Sauna: 10 min, three times a week (18 sessions), after strength or sport sessions, in two full-spectrum infrared models. Set to 50 °C 15-25 min beforehand; measured air at hip height 31.3 (4.6) °C, humidity 48 (10)%.
Heat load (pilot of 8 other people, not the participants): ear temperature rose from 36.7 to 37.2 °C in one cabin and from 36.5 to 37.1 °C in the other; weighted skin temperature reached 36.5 and 36.4 °C. Body temperature was not measured in the study itself.
Controls: foam rolling, massage, compression and NSAIDs to be avoided; diet to be kept steady; training and menstrual diaries.
Tests before and after: 20-m sprint with 5-m split; squat jump; countermovement jumps unloaded and with 15, 25 and 50% of body mass; isometric leg press; DXA; ultrasound of vastus lateralis cross-sectional area and pennation angle.
Analysis: generalised estimating equations, then t-tests within and between groups.
Funding and interests: Harvia Oyj (a sauna maker; one of the two cabins was a Harvia model), Urheiluopistosäätiö, the Ellen and Artturi Nyyssönen Foundation and the Finnish Sauna Society; the authors declare no conflict of interest. Not registered in a trial database (stated).
Key Results
| Outcome | Sauna, before → after | Control, before → after | Group × time |
|---|---|---|---|
| Vastus lateralis cross-sectional area (cm²) | 21.21 (3.15) → 22.81 (2.74), p = 0.002 | 23.17 (2.19) → 24.12 (2.91), p = 0.030 | no interaction (time effect p < 0.001) |
| Lower-body lean mass (kg) | 22.7 (2.4) → 22.9 (2.4), p = 0.041 | 22.9 (3.2) → 23.2 (3.1), p = 0.011 | no interaction |
| Whole-body lean mass (kg) | no significant change reported | 44.8 (5.8) → 45.5 (6.0), p = 0.050 | no interaction |
| Fat mass (kg) | 17.60 (5.10) → 18.2 (4.9), p = 0.048 | no significant change reported | B = −0.81, p = 0.036 |
| Body mass (kg) | 64.8 (7.1) → 65.7 (7.2), p = 0.028 | no significant change reported | no interaction |
| Jump with +15% load, height (cm) | 19.5 (3.4) → 21.0 (3.6), p = 0.006 | 22.4 (4.0) before; no significant change | p = 0.002 |
| Jump with +15% load, peak power (W) | 2519 (299) → 2690 (284), p = 0.002 | 2799 (528) before; no significant change | p = 0.010 |
| 5-m split (s) | faster, not significant (p = 0.171) | 1.133 (0.085) → 1.171 (0.123), p = 0.083 | B = −0.075, p = 0.020 |
No time, group or interaction effect for 20-m sprint, isometric leg press, or the height of the squat jump and the unloaded, +25% and +50% jumps. Peak power rose over time in the squat jump, unloaded jump and +25% jump with no interaction; within groups the +25% jump power rose only in the sauna group (from 2551 (275) W, p = 0.008).
At baseline the sauna group jumped lower with +15% load than the control group (19.5 vs 22.4 cm, p = 0.023) and showed a trend for lower peak power (p = 0.061).
Training did not differ significantly between groups: total volume 38.5 (12.2) vs 37.8 (11.3) h (p = 0.860), load p = 0.708, strength sessions 16.8 (3.9) vs 15.6 (2.7) (p = 0.286).
No pennation-angle effects.
Practical Application
Sauna after the gym and muscle growth: in 36 female team-sport athletes, 10 min of mild infrared sauna after training three times a week for 6 weeks did not change thigh-muscle growth against no sauna, so this trial shows no sign that sauna blunts gains. It tested a mild cabin (about 31 °C measured air; a 0.5-0.6 °C rise in ear temperature in a pilot, our arithmetic), not a hot Finnish sauna, and the groups were matched, not randomised.
The power signal is thin: one of five jump heights (the squat jump and four countermovement variants) showed an interaction, from a lower starting point in the sauna group, and the authors call the positive effects minor or unclear. Do not sell sauna as a power booster on this trial.
Fat mass and body mass rose slightly in the sauna group (fat mass 17.60 → 18.2 kg, with a significant interaction). The paper does not explain it; one small trial, so no conclusion either way.
The authors suggest 10 min was likely too short to warm the muscle to the 38-40 °C that, on the evidence they cite, heat-driven growth needs; that is their hypothesis, not tested here. They also caution that whole-body heat adds stress (sympathetic activity, energy expenditure, possibly sleep), citing other work, and advise tailoring the dose.
Inference, not tested here: a Finnish sauna at 80-100 °C for 15-30 min is a far larger heat and fluid load than this cabin; this trial cannot say whether that would help, harm or do nothing for muscle gain.
Limitations
Not randomised: pairs were matched on team, performance and age, and how each pair was split is not described; the loaded-jump baseline differed between groups.
Mild heat: the cabin read about 31 °C at hip height, and core or muscle temperature was not measured in the participants.
Many outcomes were tested and interactions appeared in four (loaded-jump height and peak power, 5-m split, fat mass); the paper does not describe a correction for the number of outcomes.
Six weeks, women only, mixed menstrual and contraceptive status, 5 diaries missing; no blinding was possible.
Funded in part by a sauna maker, with no conflict declared.
How this entry was checked and changed
Why this level
18 per group analysed would put a randomised parallel trial at B+; held one step lower because allocation was by matched pairs, not at random, and the paper does not say how each pair was split. Outcomes are performance and body composition (DXA, ultrasound), not markers