Heart work in the heat
- What it is
- Minutes each week your heart worked at an exercise-like level while you were in the heat.
- How it is measured
- In every sauna and hot bath round, time with heart rate at or above 64% of your max heart rate counts as moderate, and at or above 77% as vigorous: the American College of Sports Medicine's intensity bands. Max heart rate is the one set in Settings › Health & units.
- How to read it
- In a hot sauna, heart rate can reach about 150 bpm, and heart rate and blood pressure in a 93 °C sauna matched cycling at 60–100 W. Contrast shows these minutes apart from exercise: the heart works, but the body uses far less oxygen than in exercise, so they aren't converted to calories.
- What it cannot tell you
- Heart-rate zones were built for exercise. Heat raises heart rate by moving blood to the skin, not by working muscles, so the same zone means something different here. It describes the load on your heart, not fitness.
Sources
Every one of these ships inside the app, with the finding written out so you do not have to open the paper to know why it is there.
Garber CE, Blissmer B, Deschenes MR, et al. ACSM position stand: quantity and quality of exercise. Medicine & Science in Sports & Exercise, 2011.
Defines moderate intensity as 64–76% and vigorous as 77–95% of maximum heart rate.
doi.org/10.1249/MSS.0b013e318213fefbKetelhut S, Ketelhut RG. The blood pressure and heart rate during sauna bath correspond to cardiac responses during submaximal dynamic exercise. Complementary Therapies in Medicine, 2019.
In 19 adults, heart rate and blood pressure in a 93 °C sauna matched those during cycling at 60–100 W.
doi.org/10.1016/j.ctim.2019.05.002Achten J, Jeukendrup AE. Heart rate monitoring: applications and limitations. Sports Medicine, 2003.
Heat raises heart rate without raising energy use, so heart-rate-based calorie estimates fail in the heat.
doi.org/10.2165/00007256-200333070-00004