Give me a detailed protocol for heat/cold exposure using a bathtub and shower

For a bathtub-and-shower contrast routine, alternate a hot bath with a cold shower, beginning with tolerable exposures and building up gradually. There isn’t one established ideal contrast schedule, so use comfort and safety rather than forcing a target. 1 2

• 1. Hot bath: Start with about 5 minutes and gradually work toward 10–20 minutes. The heat should feel uncomfortable but not unsafe; check with your doctor before deliberate heat exposure. 3
• 2. Cold shower: Use water cold enough to feel uncomfortable but safe—not painfully icy. Start with a brief exposure, such as about 30 seconds, and build gradually; the cold-exposure guidance describes roughly 30 seconds to 1–3 minutes for many people. 4 5
• 3. Rounds and recovery: Alternate hot and cold, repeating as desired. One example is three to five rounds, but no optimal number or exact timing for contrast rounds is established. After cold, spend about 10 minutes out of the shower warming naturally rather than immediately taking a hot shower. 6 2 7
• 4. Frequency and cold bath option: The material supports cold showers five times per week in one study, but does not establish that as a universal prescription. A cold-water bath can be used instead of a shower; ease into it, since a very cold immersion can be a strong stimulus. 5 8