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In this "Ask Me Anything" (AMA) episode, Peter brings together his most up-to-date thinking on cardiorespiratory fitness into a single, practical guide designed to help listeners structure training for maximal impact on healthspan, lifespan, and long-term independence. He explains why cardiorespiratory fitness is one of the strongest modifiable predictors of longevity, clarifies what zone 2 training actually represents and how it differs from higher-intensity work, and addresses persistent confusion around exercise volume, intensity, and time constraints. The discussion covers how to measure and track progress in zone 2, VO₂ max targets and age-adjusted goals, planning for the marginal decade, and how to balance zone 2 with higher-intensity training across different weekly volumes. Peter also outlines how cardio training should be tailored for beginners, experienced trainees, and older adults, with special considerations for women and guidance on avoiding the most common cardio-training mistakes.

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We discuss:

• Rational for discussing cardiorespiratory fitness, zone 2, and VO₂ max despite having covered the topic extensively [2:30];
• Why cardiorespiratory fitness and VO₂ max are powerful and modifiable predictors of all-cause mortality compared with other health metrics [7:30];
• How age-related declines in VO₂ max constrain healthspan and everyday physical function [12:30];
• The cardiorespiratory fitness triangle: how different training intensities contribute to building the aerobic base, the aerobic peak, and overall aerobic capacity [14:15];
• The cellular mechanics of cardiorespiratory fitness: mitochondria, lactate, muscle fiber recruitment, and intensity thresholds [18:45];
• The debate over whether zone 2 training has unique benefits or whether higher-intensity exercise alone is sufficient [27:15];
• Balancing intensity and sustainability as training volume increases, and the important role of zone 2 training [32:15];
• How to identify your zone 2 training intensity [34:45];
• How to measure and track improvements in zone 2 fitness [40:00];
• How to accurately measure VO₂ max: lab testing, field tests, and the limits of wearables [45:15];
• How to set meaningful VO₂ max targets based on age, sex, long-term decline, and desired physical capabilities later in life [51:15];
• How to structure and execute a zone 2 workout [59:45];
• How strictly should zone 2 be maintained during a workout? [1:04:00];
• How to design a VO₂ max training session: interval length, intensity, recovery, and progression strategies [1:07:00];
• Why heart rate is not a reliable metric for titrating VO₂ max interval intensity [1:12:00];
• Practical ways to monitor VO₂ max improvements [1:13:30];
• How to balance zone 2 and VO₂ max training [1:15:30];
• How to structure training for someone limited to 150 minutes per week of total exercise [1:19:00];
• How to allocate 150 minutes per week of dedicated cardiorespiratory training between zone 2 and VO₂ max work [1:23:00];
• How to structure training for someone with substantial available time who wants to maximize cardiorespiratory fitness [1:24:30];
• Why spreading aerobic training across the week beats compressing volume into one session [1:26:15];
• How beginners and metabolically unhealthy individuals should start cardiorespiratory training safely [1:28:00];
• How "training age" determines the intensity and workload needed to continue improving cardiorespiratory fitness [1:31:15];
• Why zone 2 training still matters for women (including postmenopausal women) [1:32:45];
• How cardiorespiratory training should adapt with aging [1:35:45];
• The most common mistakes people make when training cardiorespiratory fitness and how to avoid them [1:37:45];
• How to break through a VO₂ max plateau [1:40:45];
• The main takeaways about cardiorespiratory fitness and longevity [1:41:30];
• Peter's carve out: oral hygiene and Peter's two-toothbrush system [1:43:00]; and
• More.

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