This podcast episode explores the complexity of heart rate zones and challenges the belief that training in Zone 3 is ineffective. It emphasizes the importance of understanding the flexibility of training zones and incorporating factors such as hydration, weather conditions, and stress levels. The episode highlights the value of rating of perceived exertion (RPE) as a comprehensive assessment of intensity and discusses the distribution of training intensity based on weekly training volume. The discussion delves into the benefits of training in Zone 3, optimizing Zone 2 training for fat oxidation, and monitoring heart rate during hot summer runs. It also explores the relationship between heat, dehydration, and heart rate, and the disconnect between performance-oriented runners and physiology-minded longevity folks. The conversation emphasizes the importance of setting specific goals, integrating challenging training sessions, and acclimatizing the body to uncomfortable conditions. The benefits of heat adaptations and the strategy of incorporating cycling into training routines are also discussed. The episode concludes with the importance of finding the right pace in running and evaluating training approaches in the context of overall training.