Haemodynamic and hormonal responses to heat exposure in a Finnish sauna bath.
Level 4 - case-series / case-control
Small within-subject physiological study without a separate control group
PubMed 2759081 · doi:10.1007/BF02330710
What was done
Eight healthy young men underwent three sauna heat exposure conditions: 80 °C dry bulb (80 D) and 100 °C dry bulb (100 D) until subjective discomfort, and 80 °C dry heat becoming humid (80 DH) until subjective exhaustion. Haemodynamic, thermal, and hormonal parameters were measured.
What was found
Oral temperature increased 1.1 °C (80 D), 1.9 °C (100 D), and 3.2 °C (80 DH). Heart rate increased about 60% (80 D), 90% (100 D), and 130% (80 DH). Plasma noradrenaline increased about 100% (80 D), 160% (100 D), and 310% (80 DH), while adrenaline did not change. Plasma prolactin increased 2-fold (80 D), 7-fold (100 D), and 10-fold (80 DH). Beta-endorphin immunoreactivity (at 100 D), ACTH (at 100 D and 80 DH), growth hormone (at 100 D), and testosterone (at 80 DH) increased, whereas cortisol decreased at 80 D and 100 D. Plasma prostaglandin E2 and serum thromboxane B2 levels showed no change.
Why it matters
This study documents acute circulatory and endocrine stress responses to sauna exposure, showing that added humidity elicits substantially greater physiological strain than dry heat alone.
Limits
The study had a very small sample size (n = 8) limited entirely to healthy young men. Exposure times were terminated based on subjective thresholds rather than standardized durations, and there was no non-heat control comparison.
Cited by
- supports Higher sauna temperatures and longer durations produce a more robust growth hormone response, up to 200° Fahrenheit.