The main goals of this episode are to shed light on the origins of zone training, illustrate how the borrowing of the models by athletes is flawed especially when heart rate is used as the primary indicator, anchor a 3-zone model to training-relevant physiology, indicate the conceptual utility of a 5-zone model, and provide you with a general guide for distributing your training intensity volumes. Full script at https://scienceofultra.com/podcasts/112