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Low Heart rate Training – Why Pros Run With A Low Heart Rate (And You Should, Too)

Despite loads of research and data supporting this or that training style, there is no one-size-fits-all solution that works for every athlete. This universal truth doesn’t discriminate, it holds true from rookie age-groupers through top-level professionals.

In a recent blog post with professional triathlete Chris Leiferman, we discussed how and why he trains almost exclusively at low intensity for the run leg of a triathlon. On paper it sounds counterintuitive, and it begs the question — how can you show up on race day ready to compete if you spend most of your time in HR Zone 2?

It obviously works — Chris won IRONMAN Boulder and IRONMAN Louisville in 2018, IRONMAN 70.3 Boulder in 2019 and is currently preparing for the IRONMAN World Championship. With Chris’ undeniable success, he got us wondering if there’s anyone else in the professional field who adheres to a similar volume-based approach.

We didn’t have to look far.

Bart Aernouts is another Polar triathlete who spends most of his time training in Zone 2. You read that right — the runner-up at the 2018 IRONMAN World Championship has been prioritizing base training for years. He’s seen his pace improve (went sub-8 hours in Kona), and has been able to train more with less of a risk of injury.

Here, we caught up with Aeronauts to discuss why he prefers this volume-based approach over one that’s intensity-based, how he determines his zones and how the conditions at Kona impact heart rate.

You spend the majority of your time training for the run in Zone 2, can you speak a little to why that works for you?

I read your blog post with Chris Leiferman, and I actually think I’m quite similar. I was always lucky to have coaches who prefer to work with this kind of approach with lots of base training. The first time I realized it worked well for me was around 2010 when I still training for short distance duathlon and triathlon and I improved my fast running in a lot of Zone 2 endurance training.

For me, it works really well to do a lot of miles in the base zone and only incorporate a few speed sessions. Just by looking at my performances, even on the fast running I improved a lot by training in Zone 2.

It might sound weird that you improve by running slow, but it’s a safe area where you can train a lot with less risk of injury, and somehow it works really well for me.

What’s your optimal ratio between slower endurance runs and higher-intensity runs?

I think I spend at least 70 percent of my time in Zone 2. The last 30 percent is either an easy jog or quality [higher-intensity] sessions.

My HR Zone 2 is also close to my race pace in the IRONMAN marathon, so it’s actually a lot of race pace, but in training it doesn’t feel like it.

If I’m in shape, I run the same pace as the marathons in the race. Of course in the race it’s different after six hours of racing, and Zone 2 is the highest you can go.

So what are some factors that influence your heart rate?

Temperature is one of the first things, and fatigue and stress does as well. If you’re tired, you’ll have a higher heart rate in basic things, and in the hard stuff you can’t reach the high heart rate.

Weather is the most important one, and this includes altitude – I’ve been training for five weeks at altitude, and it has an impact on heart rate, especially at the beginning. Heart rate is something I pay attention to, but I also try to train on feeling.

What are some other running metrics you track while training or racing?

Speed for sure, a lot of my training is based on speed zones. Of course, as I mentioned, I monitor heart rate and feeling as well. I keep it simple. I look at running power after a session, but I’m not using it while training.

I wear the Polar Vantage V, and the built-in heart rate sensor is interesting for swim training, and I often check it after the session. The battery life is something I appreciate, and I also look at what training phase I’m in because I can see if I’m overtraining or undertraining, and it’s interesting to watch and track.

I also test my VO2 quite often with my coach. I’ve been testing it for almost 13 years, and it’s all feel testing on the track. We use it to focus my overall plan, and see if I need more basic running or some faster sessions. Most of my training is based on this testing.

Is this how you figured out your Zone 2 range?

Yes, I get the speed zones and the heart rate zones from the VO2 tests. Most of my training is based on these speed zones, but of course it’s on the track so it can be a bit different elsewhere. My Zone 2 at the moment if I’m in good shape is 3:50 per kilometer to 4:15 per kilometer. My heart rate is usually between 120 and 140 bpm, but it depends on the day.

You use Zone 2 when you’re training for the run, do you use the same approach for the other disciplines?

For the swim and bike, a lot of my training is built on the same idea – a lot of endurance stuff. Cycling is built on power zones and maybe a few more effort zones, but Zone 3 works really well for me.

A lot of athletes are not confident enough to train a lot in the lower zones, and they think they need to train a lot of race pace to be faster in the race. I’ve seen based on my training that these lower zones are a great way to improve. It’s a lot about confidence.

Besides performance advantage, What other benefits does training with low HR bring?

These sessions are easy to recover from, and if you do a few quality [high-intensity] sessions, you need to make sure the quality is high. You need to train a lot in these lower zones because quality sessions needs to stay quality.

A lot of people push too hard in the easier sessions, and they can’t do as well during the quality sessions because they’re tired and not recovered properly. It’s important to do quality sessions really well, and make sure everything else is either endurance or recovery. It’s a lot about overall load, and with the lower zones you can train more and still recover well.

How do Weather conditions impact your heart rate when training and racing?

Training and racing in the heat and extreme conditions, like in Kona, affects your heart rate a lot. It’s really important to watch your heart rate and slow down the training sessions.

It’s normal if your heart rate is a bit higher in the heat, but a lot of people overtrain in the heat because they try to do similar efforts that they’re used to doing in other conditions. The elevated heart rate is a sign that it’s a lot harder for the body to perform in the heat.

how do you prepare for Kona without actually being there?

The conditions in Kona makes it hard for good training, so I go to Arizona to prepare for it. The heat is also something that can make you really tired and can ruin your race if you spend too much time in it.

I think it’s important to get used to the heat, but also recover from these sessions in a cooler environment. I try to find the balance between heat and elevation without letting it ruin my training.

It’s important to be 100-percent fit and ready to race on race day, and that’s more important than to be really adapted to the heat.

Kona has really tough conditions and a lot of athletes don’t realize how it impacts and stresses the body. They are just too tired for the race because they’ve been in the heat the whole time — you need to be fresh and rested.

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Please note that the information provided in the Polar Blog articles cannot replace individual advice from health professionals. Please consult your physician before starting a new fitness program.

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