Sauna After Your Workout Won't Kill Your Gains

No. The sauna after the gym is not killing your gains. Forty athletes trained for six weeks, half of them sitting in an infrared sauna for ten minutes after every session, and there was no interaction effect on any measure of muscle growth. Both groups grew.

A Sauna After the Gym Does Not Kill Your Gains

Ahokas and colleagues pair-matched 40 female team sport athletes into two groups in Frontiers in Sports and Active Living. Both completed the same six week strength and power block, two to three sessions a week. One group used an infrared sauna for 10 minutes at 50 degrees Celsius after training, three times a week. The other recovered passively.

Muscle was measured by DXA lean mass and by ultrasound of the vastus lateralis. Training improved neuromuscular performance and hypertrophy in both groups, and there were no interaction effects on any hypertrophy measure. The sauna neither added to muscle growth nor subtracted from it.

The sauna group did move on two performance measures across the block: countermovement jump height with 15 percent additional load (p = 0.002) and peak power (p = 0.010). Be careful how you read those. The post hoc contrasts compare the sauna group with itself before and after the six weeks rather than against the control group at the end, so the fair description is that the sauna group improved, not that it beat the other group. A 5 m split time inside the 20 m sprint also produced an interaction (p = 0.020) with no differences at all on post hoc testing.

Two limits to hold. Participants were pair-matched into groups rather than randomly allocated, so this is a controlled trial and not a randomised one. And all 40 were female team sport athletes, so nothing here speaks directly to male recreational lifters or to anyone over 40.

Heat and cold are not interchangeable just because they sit in the same corridor of your gym. We looked at the cold side separately, in what a cold plunge after lifting does to muscle growth.

Your Cortisol Spike Is Real and It Is Gone by Week Six

The standard objection runs like this. Heat is a stressor, cortisol is a stress hormone, so stacking a sauna on top of training must be adding to the bill.

The same 40 athletes were tracked for exactly that in Temperature. Morning salivary cortisol rose by 5.1 plus or minus 8.6 nmol/l after the first exercise trial in the sauna group (p = 0.017), with no increase in the control group. Post-session heart rate ran higher too, 61 plus or minus 8 bpm against 55 plus or minus 6 bpm (p = 0.019).

So the objection starts out correct.

By the last week it had inverted. The pre to post cortisol change went from +4.6 plus or minus 10.4 nmol/l at the first trial to -1.8 plus or minus 7.6 nmol/l at the final one. And muscle soreness at 36 hours after the first session was raised only in the control group, the one that skipped the sauna.

Two caveats. Those standard deviations are larger than the mean changes, so individual cortisol responses varied widely around the group effect. And this paper reports a second set of outcomes from the same 40 athletes as the hypertrophy paper, so the two are one trial rather than two studies confirming each other.

Heat Does Not Build Muscle Either, at Any Dose Anyone Has Tested

The opposite claim circulates just as hard: heat is anabolic, the sauna is a growth tool, sit in it long enough and you get bigger.

Kim and colleagues put that to the cleanest possible test. One randomly chosen thigh was wrapped in a garment perfused with water at about 52 degrees Celsius for 90 minutes a day, five days a week, for eight straight weeks. The other thigh, in the same person, was the control. It followed only twelve people, which is the main thing to hold against it.

Muscle fiber cross-sectional area: no difference between the heated thigh and the untreated one. Mitochondrial content: no difference either.

Knee extensor strength did move. Peak isokinetic torque changed by 9.1 plus or minus 16.1 Nm in the heated thigh against 4.2 plus or minus 13.1 Nm in the control thigh at week 4, and by 7.8 plus or minus 10.2 Nm against 1.8 plus or minus 9.7 Nm at week 8, with the overall difference across those timepoints significant at P = 0.007. Read the standard deviations before you get attached to that: they run two to three times the size of the means.

That heat dose is roughly 15 times the weekly exposure of three 10 minute sauna sessions, and it still produced no change in fiber size. Heat is not a muscle building stimulus in humans at any dose anyone has tested. The sauna's whole case rests on staying out of the way, which is more than some recovery tools can claim.

Heat Slowed Muscle Loss in a Strapped-Up Leg, Never in a Trained One

The next question people ask is whether the sauna protects muscle when they cannot train, through a travel week or an injury. The only human evidence sits a long way from a sauna.

Hafen and colleagues immobilised the lower limb of 23 volunteers for ten days and gave them either two hours a day of pulsed shortwave diathermy on the knee extensors or a sham treatment. It ran only ten days, and it used two hours a day of diathermy on an immobilised leg rather than a sauna, which is the caveat that decides how far this travels.

Whole muscle cross-sectional area fell 7.6 plus or minus 0.96 percent with the sham and 4.5 plus or minus 1.09 percent with daily heat (P = 0.0374). Myofiber cross-sectional area fell 10.8 plus or minus 1.52 percent against 5.8 plus or minus 1.49 percent (P = 0.0322). The treatment raised intramuscular temperature by 4.2 plus or minus 0.29 degrees Celsius, and heat shock proteins 70 and 90 rose by 25 plus or minus 6.6 percent and 20 plus or minus 7.4 percent.

Roughly half the atrophy, in a leg that was strapped up and not used. Real finding, wrong question. Nobody has tested whether a sauna protects muscle during a training layoff, a travel week or a diet. The honest answer to "does sauna protect against muscle loss" is that for a sauna, in a person who still trains, it has never been tested.

Ten Minutes at Fifty Degrees Is the Only Protocol With a Trial Behind It

Every sauna number on this page comes from one protocol. Infrared, 50 degrees Celsius, 10 minutes, straight after training, three times a week, for six weeks. A traditional Finnish sauna runs 80 to 100 degrees. Nobody has tested that after resistance training, and the evidence does not automatically travel between the two.

Stick to what the research tested:

• Type: infrared, which is what most gym saunas in Dubai run
• Temperature: around 50 degrees Celsius. If yours is hotter, start shorter.
• Duration: 10 minutes
• Frequency: two to three times a week, on training days
• Timing: straight after the session, before you leave

"I sit in the sauna sometimes" is not a protocol. Ten minutes at a defined temperature on a schedule is.

Skip It When You Are Dehydrated or Already Cooking

Not every training day needs one. Skip it when you are dehydrated and cannot fix that before you go in. Skip it when you feel dizzy after a hard session. And if you have just trained outdoors through a Dubai summer afternoon, ten more minutes of heat is not doing you any favours.

The sauna is a tool, not a ritual. The trial ran three sessions a week, so missing one changes nothing.

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