Thirty young men (22.67 ± 2.02 years), physically active and regular sauna users, completed four 12-minute sessions at 90–91 °C and 14–16% relative humidity with four 6-minute cool-downs — about 72 minutes of thermal stress in total.
Cardio and blood work
Mean HRavg sat at 102.5 bpm (easy-effort range); HRpeak 143.3 bpm (very hard). Systolic BP fell by 9.7 mmHg, diastolic by 6.9 mmHg (p < 0.001). Significant rises: pO2, total cholesterol, HDL and LDL. Significant falls: pH, bicarbonate measures, base excess, ctCO2, glucose and lactate. Body mass dropped from sweating — the clearest “change” in an otherwise stable physiological picture.
Practical takeaway
In prepared, habitual male users, this long session did not smash homeostasis. That is not a licence for unsupervised heroics, cardiac risk groups or first-timers. Women and other populations were not studied here.
Why physiotherapists care
Heat is a dose. If you prescribe contrast or sauna adjuncts around training, these effect directions (BP down, mass down, lipids shifting acutely) set expectations for what “normal recovery numbers” look like the same evening.
Participants already used saunas regularly — adaptation is part of the result. Anthropometry, physiology and haematology were sampled around the four-bout protocol. Easy-range average heart rate with very-hard peaks is the signature of intermittent heat: recovery windows matter as much as the hot room.
Acute rises in HDL and LDL together with total cholesterol are session effects, not a six-month lipid clinic report. Same for the bicarbonate and base-excess shifts: expect them if you blood-test the same evening.
Hydration and medical screening remain non-negotiable. The paper’s safety message is conditional on prepared males; it is not a viral “90°C for an hour is always fine” clip.
Participants already used saunas regularly — adaptation is part of the result. Anthropometry, physiology and haematology were sampled around the four-bout protocol. Easy-range average heart rate with very-hard peaks is the signature of intermittent heat: recovery windows matter as much as the hot room.
Acute rises in HDL and LDL together with total cholesterol are session effects, not a six-month lipid clinic report. Same for the bicarbonate and base-excess shifts: expect them if you blood-test the same evening.
Hydration and medical screening remain non-negotiable. The paper’s safety message is conditional on prepared males; it is not a viral “90°C for an hour is always fine” clip.
Where this sits in the lab
Biokineticum’s public notes exist so practitioners can reach the DOI without drowning in jargon — and so athletes, teachers and clinicians see that combat-sport science also publishes on prisons, faith, fair play, sauna physiology and disability policy. Soft topics still deserve hard methods: sample sizes, instruments, effect directions and explicit limits.
If you teach, treat or coach from these findings, copy the reference list into your syllabus, open the full text, and write down what you will measure next week. That is the only CTA that always fits.
Reading notes
Psychosocial and public-health papers describe associations in defined samples — not moral verdicts about individuals. We keep the language descriptive, avoid stigma, and point you to the DOI for methods and limits.
If the topic touches your clinic, classroom or programme design, treat this post as a map to the paper, not a substitute for it.
References
- Podstawski R, Borysławski K, Pomianowski A, Krystkiewicz W, Boraczyński T, Mosler D, Wąsik J, Jaszczur-Nowicki J. The Effects of Repeated Thermal Stress on the Physiological Parameters of Young Physically Active Men Who Regularly Use the Sauna: A Multifactorial Assessment. International Journal of Environmental Research and Public Health. 2021. 18(21):11503. doi:10.3390/ijerph182111503
Measurement-led biomechanics, health psychology and clinical tools at Biokineticum.
