Contrast therapy, a practice of switching between heat and cold (such as a sauna followed by a cold plunge or shower), is used for exercise recovery and as an everyday health habit. Its clearest benefit is less muscle soreness, and probably faster strength return, after hard exercise versus resting, not versus cold water alone. Major longevity claims rest on sauna studies; added value over heat or cold alone is unproven. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Resting blood pressure | Below 120/80 mmHg | Safety check: high or unstable values change use |
| Glucose (insulin users) | 70–99 mg/dL fasting | Safety check: low values pause sessions |
| Semen analysis (men seeking conception) | Sperm concentration at least 15 million/mL; total motility at least 40% | Safety check: falling values pause heat phases |
| Creatine kinase (athletes) | No established target; change from own post-exercise baseline | Expected to be lower 48 hours after contrast recovery |
| Body weight before and after a session | No established target; loss against own pre-session weight | Safety check: large sweat loss signals dehydration |
Cadence: Resting blood pressure at 1 week, 4 weeks, then every 3–6 months; glucose at every session for the first 2–4 weeks in insulin users; semen analysis about 3 months after starting regular heat phases; body weight at each session during the first month