Dr. Leo Runnin opens with a phrase that stopped me the first time I heard it: "Heat training is like poor man's altitude training." That's not just a clever analogy. It's a mechanistically accurate description of what happens when you sit in a hot room long enough for your body to start adapting.
At altitude, your body responds to reduced oxygen by producing more red blood cells, expanding plasma volume, and growing more capillaries to deliver oxygen to working muscles. Heat does nearly the same thing through a different pathway. Your cardiovascular system has to push blood to the skin surface to dissipate heat — and over time, your body responds by building more infrastructure for that job. More capillaries. More plasma. A more flexible, responsive circulatory system. Athletes have known this for decades. It's why Finnish cross-country skiers were using saunas as training tools long before sports science caught up with them.
Everything Dr. Runnin describes about heat shock proteins, capillarization, and lactic acid clearance aligns cleanly with the academic literature we have indexed here. A 2025 study on Finnish sauna and cold water immersion showed that repeated heat cycles produce measurable adaptive effects on cardiovascular resilience — your heart literally becomes better at handling stress over time. Not just thermal stress. All stress. And the dose-response data from the Finnish population cohort studies is consistent: four to five sessions per week is where the meaningful gains appear.
The timing framework he proposes — heat in the evening, cold in the morning — also has solid mechanistic grounding. Your core body temperature follows a circadian rhythm. It needs to drop to initiate deep sleep. A sauna session in the evening heats you up, and the subsequent cooling amplifies that natural temperature drop. The data on this is surprisingly consistent across multiple researchers.
The one area I'd add texture to is the cold timing question. Dr. Runnin recommends cold exclusively in the morning, but the contrast therapy research is more flexible on this point. When you're doing deliberate hot-cold cycling — true contrast therapy — the order and timing matter less than the oscillation itself. The Contrast Collective protocol is built on that oscillation. The transition between states is where much of the benefit lives: the vasodilation-vasoconstriction cycle, the catecholamine flush, the autonomic nervous system reset.
So if morning cold is your preference, excellent. But don't let scheduling rigidity keep you off the protocol entirely.
Four sessions per week, twenty to thirty minutes each, sauna temperature between 160 and 200 degrees Fahrenheit depending on what type you have access to. If you're doing standalone sauna without contrast, do it in the evening. If you're doing contrast therapy — heat followed by cold — the timing is more flexible, and the combination amplifies every mechanism discussed here.
Don't overcomplicate the entry point. A hot bath before bed is a legitimate starting protocol if you have no other access. The body responds to the stimulus regardless of the vessel delivering it.
What stays with me from this conversation is the cupping-plus-sauna observation. On the surface, combining these seems like stacking wellness modalities for the sake of it. But there's something real happening here. Heat changes tissue viscosity. Fascia and muscle are genuinely more pliable at elevated temperature. Tools that work on soft tissue — cupping, massage, even stretching — produce deeper effects when the tissue is warm. This is why contrast therapy clinics that layer manual therapy into their protocols see outcomes that neither therapy achieves alone. The heat isn't just preparing you to relax. It's preparing your tissue to respond. That's a meaningful distinction.