Steve House sits down with Dr. Marco Altini — data scientist, physiologist, and founder of HRV4Training — for a deep-dive into one of the most misunderstood tools in endurance athletics: heart rate variability. With over 50 peer-reviewed papers to his name, Dr. Altini brings rare scientific rigor to a space crowded with oversimplified wearable metrics. The conversation opens by challenging the industry's obsession with single-number readiness scores, which Dr. Altini argues dilute nuanced physiological signals into deterministic assumptions that don't reflect the complexity of the human body.  

The episode unpacks the fundamentals of HRV — what it actually measures, why morning is the optimal measurement window for endurance athletes, and how to interpret it as a marker of stress response rather than performance capacity. Steve and Marco also cover hardware accuracy across chest straps, optical sensors, and phone cameras; HRV research at altitude; and the broader question of how biometric data should support — not replace — the athlete's own sense of feel.

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