Yes, Science Says HRV is a Triathlete’s Secret Weapon

Train less, improve more. Isn’t that the holy grail for endurance athletes?

What if the solution to make that possible has been here for a long time and might live inside the smartwatch on your wrist?

A new study from the National Institute of Fitness and Sports in Kanoya, Japan, has once more proved that an HRV-guided training program can yield the best return on investment for athlete development. Even better, it does so with a lower training volume. This sounds like a win-win for busy triathletes trying to manage the moving target of training and rest.

The study

The Japanese researchers divided 12 active men into two groups (more on the sample size below): one group followed an HRV-guided aerobic training program for five weeks, while the other adhered to a Block Periodization approach, which employs a more “standard” method of loading and tapering weeks.

The athletes followed the same program during the first week to get accustomed to the sessions. Then, in weeks two and three, the load for the Block group was increased by 40%, while the HRV group was given low or high-intensity sessions based on their daily HRV measures.

Finally, on weeks 4 and 5, the BP load was reduced by 50%, whereas the HRV group continued based on individual variations and adaptations.

“If HRV remained low after completing low-intensity training, a rest day was assigned,” explains Professor Yohei Takai from the research group. “If HRV stayed low even after a rest day, an additional rest day was provided. Following two consecutive rest days, low-intensity training took place the next day.”

The results

To monitor training progress, the researchers conducted two types of tests before the training program began, at the end of each week, and at the end of the tapering phase.

After five weeks, both groups showed an increase in maximal and submaximal power. The HRV group boosted their power to the same level as the BP group but with lower strain (around 25%), generally lower volume, a reduced training impulse (a product of volume and intensity), and less time spent at or above the lactate threshold.

Interestingly, the HRV group showed less individual variation than the second group, suggesting that athletes respond quite differently to specific volumes during a standard block period (the same applied to everyone).

Limitations

As Takei and his team note at the end of the study, there were limitations. First, the sample size was small, which is often the case in sports-related research.

Second, the participants were not high-performing athletes, and the adaptations may vary among elite groups. Additionally, all participants were young males accustomed to running, but they were tested on a cycling ergometer. This decision, once again, stemmed from the university’s access to testing equipment and the availability of athletes:

“Our university has a higher number of male students, and as a sports university, many students participate in athletic competitions. To eliminate the effects of different sports training, participants were selected from the same sport (soccer). That’s why only male participants could be recruited,” Takai explains. “On the other hand, the cycling ergometer allowed for easier control of training volume and, given the large number of ergometers available, enabled multiple participants to train simultaneously.”

For triathletes, Takei notes that the findings may also be significant, but this depends on whether they train in all three disciplines daily (probably not even all professionals or elite age group athletes) or alternate between them (which is typical for most of us). “If it’s the former, I believe it would be suitable to follow HRV-guided training,” he states. “In the latter scenario, it’s essential to understand how heart rate variability varies after training in each discipline and adapt accordingly.”

Still good news for triathletes?

“The study confirms what we already know about heart rate variability guided training, which usually offers a superior outcome in terms of the adaptations. And despite the small sample size, they found significance over several weeks,” says coach and exercise physiologist Paul Laursen, who has researched and used HRV in endurance sports for more than two decades and co-authored the popular Science and Applications of High-Intensity Interval Training.

Laursen also explains that using HRV is relevant whether you’re a runner, cyclist, swimmer, or triathlete and that the findings of Takei’s study can be easily applied to triathletes. By measuring and monitoring your HRV daily and adjusting your training according to your HRV trends, HRV-guided training will provide the best adaptations.

HRV and AI

Laursen also uses an AI platform he developed, athletica.ai, with his athletes. Athletica is built around HRV readings and patterns and automatically adapts your daily training based on your morning readings. However, the crucial aspect of how Laursen works with his athletes is looking at long-term patterns, not single readings, and always incorporating human interpretation of the data displayed.

“First, we have to credit Marco Altini for this job (he’s a real HRV guru, and you can check him out here), who’s done a good job of forming this method,” Laursen says. He explains that if the seven-day HRV average rises above the 60-day range, it signals positive adaptation and recovery. If it drops below, it indicates excess stress and a need to take action.

In these particular instances, either the AI calculations or Laursen himself would alter the athletes’ training programs by recommending an easy session, a rest day, or even meditation to help relax and restore parasympathetic activity.

“AI is supporting us,” he explains. “So the AI is the assistant coach, but the personal touch is so important. Some athletes can’t afford a coach, so they can get a lot of insight and help by just having an AI coach. But some people still need that coach. So we need expert coaches who understand this, can pick up the phone, or send WhatsApp, or can explain why you might need a rest day or do a mediation session.”

HRV training tips

The scientific literature increasingly highlights the advantages of HRV-guided training programs in sports. Try it out if you’ve never used HRV and want to give it a shot. Also, don’t fret if you don’t have a coach or an AI platform to customize your training plan. Laursen still has a few golden nuggets to help you get started and achieve more with less:

1. Be consistent with your readings. If your smartwatch doesn’t track them and you need to measure, do so in the morning: wake up, empty your bladder, lie back down, and take the measurement. The more data points you have over time, the better.
2. Never compare your HRV to someone else’s. Yours is unique; it’s relative rather than an absolute value (different devices use various mathematical models to calculate it, and some are more accurate than others).
3. Don’t react based on a single outlier. One bad day or one good day doesn’t mean much. What matters is the aggregated data over 60 days and 7 days.