Zack Kelly: Making Sense of HRV, Wearables & Performance Data

Zack Kelly is a performance coach and psychophysiologist who specializes in helping clients interpret and apply performance data. His master's research focused on heart rate variability, and he works with athletes and everyday clients to optimize training using metrics like HRV, force plate testing, and VO2 max assessments.Zack discusses what heart rate variability actually measures and why wearable devices often misinterpret the data. He explains why high HRV isn't always a sign of good recovery, how blunted HRV responses can indicate underlying health issues, and why tracking trends over time matters more than daily scores. The conversation covers force plate testing for detecting asymmetries and injury risk, the psychological pitfalls of becoming too data-dependent, and how to build a healthy relationship with wearable technology. Zack shares practical strategies for using metrics effectively, including focusing on one variable at a time, looking at big-picture trends rather than daily fluctuations, and knowing when to trust your body over the numbers.00:00 - Intro01:37 - What Is HRV and Why Does It Matter?03:33 - Why High HRV Isn't Always Good05:34 - Blunted HRV Response in Clinical Populations07:46 - Addressing Asymmetries With Force Plate Testing12:55 - The Danger of Over-Interpreting Data19:05 - When to Actually Pay Attention to Your Numbers22:56 - Understanding Zone 2 Training28:00 - How to Use Wearables Without Obsessing35:24 - Preparing for VO2 Max Testing40:06 - What Performance Coaches Actually Track