Eleven minutes of cold per week. Three sauna sessions for cardiovascular benefit. A 200 to 300 percent increase in dopamine and serotonin from cold exposure. These numbers get repeated a lot in the contrast therapy space, and they're accurate enough. But the more I sit with this conversation between Dr. Addie and Dr. Jace, the more I think the headline is buried in the setup — the AI-generated 4-week protocol they mentioned almost in passing.
Cold in the morning for hormonal activation and dopamine boost. Heat in the afternoon or evening for parasympathetic recovery and sleep. That's not a random combination. That's a deliberate alignment with your circadian biology, and it mirrors exactly what the research tells us about temperature and the nervous system.
Here's what I keep coming back to: it's not really about whether cold is better than heat, or whether you need both. It's about when you apply each stimulus relative to your nervous system's natural rhythm. Your core body temperature is lowest in the early morning hours and peaks in the late afternoon. Cold in the morning accelerates the temperature drop from sleep toward wakefulness — it sharpens the transition. Heat in the evening amplifies the natural temperature fall that signals your brain to initiate sleep. You're not fighting biology. You're riding it.
The hypertrophy caution Dr. Addie raises is real and worth taking seriously. The research is unambiguous on this: cold therapy within a few hours of a heavy strength session suppresses the inflammatory cascade that drives muscle protein synthesis. Inflammation isn't always the enemy. Sometimes it's the signal. Block the signal too early and you've trained hard for diminished returns. Twenty-four hours is the conservative threshold. Most practitioners now say at least six to eight hours minimum, though the literature is still sorting this out.
There's genuine consensus forming around a few things. Heat exposure — whether sauna or hot tub — provides measurable cardiovascular adaptations that mirror aerobic exercise. Blood plasma volume increases, vasculature dilates, heart rate climbs into aerobic zones. For people who can't train intensely due to injury or joint issues, this matters enormously. Three sessions per week is the threshold where the Laukkanen data from Finland starts showing meaningful mortality reduction. That's accessible for almost anyone.
Cold, meanwhile, has the neurochemical edge. The norepinephrine spike from cold exposure is one of the most reliable and sustained mood-altering mechanisms we know of — no supplement comes close. And unlike caffeine, it doesn't build tolerance at the same rate if you vary your exposure temperature and duration.
Don't start with eleven minutes. Start with two. Two minutes of cold water at the end of your morning shower, six days a week. Build the habit before you build the duration. Once that feels manageable — not easy, just manageable — extend to three minutes, then four. Your nervous system adapts. The benefits scale with tolerance, not with suffering.
For heat, evening is your friend if sleep is a priority. Thirty minutes in a sauna or even a hot bath two hours before bed, followed by cooling down in ambient air, creates a thermal signal that deepens slow-wave sleep. If you're doing contrast therapy, finish on cold. You want the sympathetic rebound from cold to be temporary, not something you're still riding when you lie down.
The AI protocol angle in this conversation is easy to gloss over, but it points at something important. The hardest part of contrast therapy isn't the cold water. It's the periodization — knowing when to apply which stimulus relative to your training load, your sleep quality, your stress levels. Wearables like Whoop and Oura are starting to give us real-time readiness data that can inform these decisions. The next step is using that data to dynamically adjust protocols, not just track them. The hosts glimpsed this and moved past it. I think it's actually the most interesting frontier in the space.