This video explains that vigorous intensity exercise, specifically high-intensity interval training (HIIT), is the most effective way to improve cardiorespiratory fitness and reverse age-related changes in the heart. It contrasts HIIT with moderate-intensity exercise, highlighting studies showing that HIIT leads to greater cardiovascular adaptations. The video also details specific HIIT protocols, such as the Norwegian 4x4 and a 1-minute on/1-minute off interval, and discusses how exercise can combat heart stiffening caused by glycation.