Cardio isn’t just running on a treadmill—it’s one of the most misunderstood parts of fitness. In this episode, Dr. Quartell breaks down the real science behind HIIT and Zone 2 training, why both are essential, and how to combine them for maximum strength, endurance, fat-burning, and longevity. If you’re tired of guessing what “good cardio” really means, this is the clear, practical guide you’ve been waiting for.