When to Use Zone 4–5 Intervals

Dr. Erin joins Wild Health coach Steve Holt to unpack VO₂ max—what it actually represents, why it's closely tied to all-cause mortality, and how heart, lung, vascular, and mitochondrial function all contribute to it. They walk through practical ways to build an aerobic base, use interval work to raise your threshold, and apply zone-based training with or without wearables. The conversation focuses on evidence-informed methods to improve cardiorespiratory capacity in a sustainable way, whether you're new to training or already well-conditioned.