How much cardio should you do, and does more of it ever become harmful? Cardiorespiratory fitness keeps improving with training load and nobody has found a ceiling. Getting fitter keeps lowering mortality risk as far out as anyone has measured. The one dose dependent harm that survives scrutiny is atrial fibrillation, and it shows up around six to seven hours a week of hard endurance training sustained for years.
This episode goes through the Danish jogging study behind the “fast running is as deadly as sitting on the couch” headlines and why two deaths in forty people can’t carry it, the much larger datasets that found no harm signal, and what changes when somebody measures fitness on a treadmill instead of asking people about minutes. Then atrial fibrillation, coronary calcium and heart scarring in lifelong endurance athletes, the sudden cardiac arrest numbers from 29 million race finishers, whether cardio interferes with lifting, fuel handling, weight loss and metabolic compensation, and bone density in cyclists. It closes with a rewritten version of the cardio guidelines, including volume, intensity, progression, and the fitness and health targets the real guidelines leave out.
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