Chasing the Perfect Score

Written by James Witts, content writer for Nopinz.

Mathieu van der Poel, Lucy Charles-Barclay, Rory McIlroy, Aryna Sabalenka, Cristiano Ronaldo, the entire Paris Saint-Germain football team… the breadth and depth of sporting superstars sponsored by Whoop is breathtaking. Throw in another 2.5 million members worldwide and you can see why its latest valuation came in around £7.5 billion. It’s a similar story at fellow wearable behemoths Oura, who reportedly sold over 5.5-million rings between 2015 and 2025, valuing them at a rather cool £8 billion.

Wearables are big business – as many Nopinz riders, runners and triathletes well know because there’s a very good chance that you’re one of the many whose first act upon waking is checking how they slept. Data, it seems, is profitable. And appealing. But is it Queen/King? In other words, is it accurate and, if so, what can you actually do with that data to make you a stronger, healthier athlete?

Endurance athletes are an important demographic for wearable manufacturers as they know we’re already tapped into the data ecosystem. Take cycling. There’s a very good chance that you’ll have a power meter that sends wattage information to your cutting-edge bike computer, which helps you to pace your TrainingPeaks-prescribed session by displaying upcoming gradients. You understand the benefits of data on optimising your training.

But what about the benefits of Whoop, Oura and co that impact performance, but often indirectly by focusing more directly on recovery?

One proponent is Canadian track cyclist Nick Wammes. The 26-year-old has won team-sprint gold medals at the Pan American Games and Pam American Championships, plus he competed at both the 2020 Tokyo and 2024 Paris Olympics.

Wammes uses Whoop and, unlike the protagonists above, isn’t paid to do so. “I’ve been using Whoop for just over three years,” he tells us. “The two features I use the most and monitor on a daily basis are heart rate variability and sleep.”

If it works for a multi-Olympian, it works for us. So, that’s where we’ll focus our wearable lens. However, both are also huge topics, especially for the endurance athlete. That’s why this blog will focus on heart rate variability and the next will focus on sleep…

What is HRV?

Heart rate variability, or HRV, is seen in nearly every wearable and sports watch, and reflects the balance of your autonomic nervous system, which has two branches: your sympathetic, or ‘fight or flight’, system and your parasympathetic system, which is your ‘rest and digest response’.

HRV examines the variation in heart rate from beat to beat. That’s because even when your heart rate is stable – say 60bpm – the gap between beats isn’t precisely one second. It varies and this links back to the autonomic nervous system.

A higher HRV – higher variance between beats – is associated with greater parasympathetic activity and adaptability; a decrease in HRV – less variance between beats – is a sign of high stress, which could be a sign of illness, sleep deprivation, heavy training or dehydration. Wearables often convert HRV into ‘readiness’ or ‘recovery’ scores, but these scores are user-friendly interpretations rather than direct physiological measurements.

Factors that affect HRV

The first rule of optimising HRV is knowing you are unique. “HRV is impacted by many factors. But, in general, it reduces over decades,” says Marco Altini, founder of popular HRV app ‘HRV4Training’ and considered one of the world’s leading experts on HRV. “It’s similar between men and women, despite a typically higher resting heart rate in women. HRV might change a little with fitness. HRV also has a strong genetic component, which is why you shouldn’t compare your results with others.”

“It’s also very sensitive,” adds Altini. “For instance, late exercise results in increased heart rate for several hours during sleep, which is no problem, but would be captured as a negative response by wearables measuring in the night. Often, night data is more tightly coupled with our behaviour than with our stress response and therefore is less useful for daily guidance.”

That’s not to say you should dispense with your nighttime-measuring wearable. Instead, it highlights a key wearable theme – that you should look for trends rather than act on one day’s outlier.

The more data you gather, the more you can see how you’re responding over time. If you’re constantly registering low HRV numbers, ask yourself: am I under-fuelled? Am I feeling on the edge of sickness? Am I experiencing unusual lifestyle stress?

Real-life HRV example

When EF Pro Cycling and Whoop had an official partnership, Neilson Powless explained how he became ill with COVID and noticed a pattern of decreased HRV, elevated resting heart rate and increased respiratory rate compared with his normal baseline. These changes, together with his symptoms and advice from team doctors, influenced decisions to rest and withdraw from racing. As the metrics returned towards normal, he gradually resumed training.

Powless’ HRV data also resulted in a shift in eating behaviour. Historically, he’d eat light meals during the day and enjoy a big dinner later on. But he noted that this pattern reduced his HRV scores and impeded his recovery.

“If I have a light dinner, my values are better in the morning,” he blogged. “So, I started to eat heavier breakfasts and lunches, and at dinner I don’t overdo it. There are normal meals and then there are endurance-athlete meals. Breakfast and lunch are my endurance-athlete meals and dinner is my meal as a normal person. It’s helped my values because my body’s not working so much through the night to digest the massive amount of food that I’ve just eaten.”

In the historic blog, Powless emphasised that a single low HRV value isn’t very meaningful – it’s the sustained changes over several days that are useful. In other words, again, focus on trends rather than one-offs.

Influencing your intensity

So, HRV can play a role in gauging your state of health. But what about impacting your training? Wammes says that when he’s in a training phase, it’s rare that he’ll change training sessions on a day-to-day basis unless he and his team notice significant trends. “We have used HRV data to modify certain areas of competition preparation and monitor how I’m trending into a race,” he says.

Darren Morris, lead practitioner at Inochi Longevity who’s completed countless triathlons, is a Whoop convert and uses it with many of his clients. He suggests HRV has a fanbase of practitioners who feel it has a role to play in training.

“There’s an emerging group of advocates for HRV as the main determinant of a training programme,” he says. “How does that work? Say on a Wednesday you typically do your easy base session but you’ve woken to a good recovery score, which is usually a sign of a good HRV score, you might want to do your high-intensity effort instead. For instance, I was going to go for an easy run this morning, but I awoke to 94% recovery and felt good, so did my Norwegian 4 x 4s [which involves 4min sets of intense cardio followed by 3 min of light exercise repeated four times. It’s usually sandwiched between a 5min warm-up and 5min cool-down.

“My scores might not be as good tomorrow, which isn’t to say I wouldn’t have done the Norwegian session, but I’m just being guided by – and seeking to optimise – my physiology. And even if I wake tomorrow with a 60% recovery or lower HRV score, I know that I’ll be able to do my zone 2 run without pushing myself into overtraining, which wearables can also help with.”

Altini agrees that HRV is useful for making small adjustments to training intensity and in support of a training plan. “Just bear in mind that HRV isn’t about what you can do on a given day (i.e. unless you’re sick, you can typically perform well on a ‘low HRV score’). It’s mostly about what stress you can assimilate and respond positively to,” he says. “If it’s race day and your HRV is low, there’s nothing to worry about, as you can still perform. During a training block, though, working hard in a situation of low HRV might not result in the hoped adaptations, as you’re already in a sub-optimal physiological state. Many HRV-guided studies have shown this, in which the group of athletes that performed fewer high-intensity sessions, by reducing training intensity on days in which HRV was below their normal range, ended up performing better at the end of the study.”

AI and HRV

HRV is one area where artificial intelligence (AI) can play an increasing role in making sense of HRV readings and how they apply to your training plan.

Stride, the newest kid on the AI block, takes into account wearable HRV data when assessing training and planning upcoming sessions. Rather neatly, it analyses an athlete’s historical response to training and racing load to calculate the effect on HRV. The detail of Stride is impressive. And not surprising as it’s co-founded by former professional and good friend of Nopinz, Alex Dowsett.

Athletica uses HRV as one of several metrics to tailor training recommendations. Rather than responding to a single day’s HRV reading, the platform focuses on longer-term trends alongside factors such as training load, sleep, illness and session completion. If sustained changes in HRV suggest increased fatigue or reduced capacity to adapt, Athletica might recommend modifying upcoming sessions, reducing intensity or prioritising recovery. The aim is to balance training stimulus with recovery to support consistent progression while minimising excessive fatigue.

Vekta, used by an increasing number of WorldTour cycling teams and invested in by Chris Froome, is another AI-fuelled outfit that uses HRV, albeit as part of a broader picture of an athlete’s readiness and response to training rather than as a standalone trigger for changing sessions.

Accuracy of measuring HRV

Of course, all of this HRV feedback is redundant if accuracy’s off. Morris says in his experience, Whoop’s HRV is within 5-10% accuracy of Firstbeat’s clinical-grade electrocardiogram (ECG)-based HRV monitoring. “I don’t know about the rings, though,” he says.

A 2025 study does. It focused on nocturnal health metrics, including resting heart rate and heart rate variability. The Garmin Fenix 6, Oura 3 and 4, Polar Grit X Pro and Whoop 4.0 were compared against the gold-standard ECG. The Oura offerings were the most accurate, followed by the Whoop. Polar and Garmin languished at the bottom.

Talking about ‘resting heart rate’, you might ask what advantage there is in monitoring HRV compared to resting heart rate, which is historically deemed a reliable gauge of wellness (a higher resting heart rate is a sign that your body is under stress through overtraining, illness or life stress)?

“Both heart rate and HRV are useful markers of our stress response as well as changes in fitness over time,” says Altini. “The reason to look at HRV and not only at resting heart rate is that HRV tends to be a more sensitive marker of stress, often capturing changes that aren’t visible or too small in resting heart rate. My recommendation would be to look at how both of these signals change over time and in response to acute stressors, together with the relevant context, be it training or lifestyle.”

Where does that leave us? The key is that you don’t focus on daily HRV scores but look at trends. Don’t obsess about the data to the point that it’s ruining your life. It’s part of the performance picture, not the whole picture. You must maintain your intuition. In fact, marrying your HRV data while knowing oneself is the sweet spot that will pay the greatest dividends, says Olympian Wammes. “Over the years, Whoop has helped me to develop my instincts of what works and what doesn’t. For me, it’s an essential tool in the toolbox to help me become a better athlete.” Which, adds Wammes, is also down to his wearable data, this time improving how he sleeps – a potentially performance- and health-changing topic that we’ll focus on in part two of ‘Chasing the Perfect Score’…

 

–  This post was written by James Witts.

James Witts is a writer who specialises in endurance sport and sports science. He has three books on his palmares including The Science of the Tour de France and Riding with the Rocketmen. He also writes for a broad range of consumer publications including Rouleur, Cyclist, The Observer and 220 Triathlon.