Welcome to Playbook, a Q&A series where I ask successful guys about their wellness philosophy. This week I’ve got Dan Plews, an applied sports scientist, elite endurance athlete, performance advisor for Climatic and author of Heart Rate Variability: Science and Strategies for Peak Performance.
Tanner Garrity: Any fitness goals you’re chasing right now? What does an average training week look like for you these days?
Dan Plews: Right now I’m chasing a podium at Hyrox Worlds 2027 on the doubles, and sub-60 in the Hyrox Pro. My training reflects that: I’m running four times a week, mixing long aerobic work with shorter, higher-intensity efforts, and I’m in the gym two to three times a week working on the functional strength that Hyrox demands. I still also include cycling a lot. For an endurance athlete who spent 25 years focused on swim, bike, run, adding meaningful strength work without wrecking your recovery is a real balancing act.
That’s where HRV [heart rate variability] comes in for me. I track my RMSSD [root mean square of successive differences] every morning and my goal for this block has been to raise my baseline while keeping the day-to-day variation low, which signals that my body is absorbing the training rather than just surviving it. I’ve been using L Max from Climatic as part of my daily routine and I’ve genuinely been surprised by what I’ve seen in my HRV data. My baseline has been climbing and stabilizing in a way that’s made me more confident in pushing the training. Whether that’s the cumulative effect on airway health, the reduction in environmental load on my autonomic nervous system, or a combination, I can’t be certain, but the signal is there and I trust the data.
What does HRV reveal about an athlete’s physiology that their times or power numbers can’t?
Your power numbers tell you what you did. HRV tells you what state your body is in to do it again. More specifically, HRV, and here I mean RMSSD, the measure most apps use (Whoop, Oura, HRV4Training, etc.), reflects your cardiac vagal activity. It’s a window into your parasympathetic nervous system, into how much capacity to take in more stress you actually have rather than how fit you appear to be. The number I care about most in the book we wrote on HRV is something we call the “Vagal Tank.” It captures your body’s overall capacity to respond to stress and return to baseline. A full tank means you absorb training and adapt. A chronically low tank means you’re accumulating fatigue without the gains.
What do you know about performance in your 40s that you wish you knew in your 20s?
Recovery is work. In my 20s, I thought the training was the work and recovery was just what happened in between. Now I understand they’re inseparable. Your ability to adapt is only as good as your ability to recover, and in your 40s that window gets narrower. You feel the effects of poor sleep, alcohol and accumulated environmental stress faster.
That last one is something I’ve paid much more attention to recently. Lung health is not something endurance athletes talk about nearly enough. We spend a lot of time optimizing nutrition, sleep and training load, but the air quality you’re training in every day is constantly placing a load on your autonomic nervous system that most people ignore entirely. Having said that, though, I still feel like I’m in my 20s. (After all, my Whoop age is 27.) But now I pay way more attention to the smaller aspects of performance and recovery.
What did your Ironman background prepare you for in Hyrox, and what did it leave you unprepared for?
Ironman gave me the aerobic base, the race-day composure. Those things transfer directly. Knowing how to pace, how to fuel under pressure, how to stay mentally calm when it hurts, that’s all the same. What it completely failed to prepare me for was the stations and upper-body strength. I was a pure endurance athlete. My cardiovascular system was exceptional; my strength, particularly my upper body, wasn’t great (and still isn’t that great to be honest). The neuromuscular demands of Hyrox are something you can’t fake with aerobic fitness. In Ironman you can dial back on the bike and manage. In Hyrox you hit a station and you’re either strong enough or you’re not. That required a completely different kind of preparation that I’ve had to build from scratch.
More Like This
Twice a week, you'll find proven advice and tips, expert interviews, deeply reported features and personal essays on living better — for however long you’re here. Subscribe to Champ now.