Does Heart Rate Training Really Work?

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Heart rate zone training and VO2 - Does it really matter?

Does it matter if we count calories? Do we really need to be focused on training VO2? These are some really great interactions and questions that I've gotten over the last week from my athletes and even strangers on the internet. I want to give you guys a breakdown of my thoughts on these things. As always, I'm going to give you what I know or have read through the research, but I'm also going to give you some observational insight and things that I've seen in my actual practice. And then I'm going to give you some opinion also.

Now most of the time, this is how all of my podcasts are typically structured. But I want to make this absolutely clear here. If you have read something contrary to what I'm talking about, if you have a different opinion or you’ve seen something different in practice, please feel free to share in the comments and let's have a conversation about it. I am always agreeable to discussion and I'm always open to having my mind changed.

So does heart rate zone training or paying attention to your heart rate zones actually matter? Does what your Garmin says about your heart rate zones or whatever other fitness device you're using really matter? Why do we even check heart rate zones? A lot of you probably have some type of fitness device. Garmin is really popular and shows you training zones from zone 1 through 5. Zone 2 training is a big topic right now with an emphasis on doing a lot of zone two to improve aerobic fitness, cardiorespiratory fitness, and VO2 base.

I get a lot of athletes and people in my DMs who say they feel their heart rate zones are inaccurate. Some believe heart rate zones are meaningless while others are diehard about staying in their exact zones.

So is heart rate zone training appropriate, accurate, or even worth paying attention to?

I would say yes.

Just like tracking calories or macros, heart rate zones can provide guidance and insight into where we currently are in training.

In the lab we bring athletes in, test their VO2, and establish heart rate training zones. The way we do this for trained or experienced athletes is by using a percentage of their VO2 max to determine their zones. Fitness devices and calculators often use age-related formulas like 220 minus age or heart rate reserve techniques. For trained people, this is usually not accurate. When we do direct testing by gas exchange, we’re measuring how much oxygen you consume at a specific heart rate and also CO2 to look at substrate utilization. This shows where your aerobic threshold, anaerobic threshold, or ventilatory thresholds are on the day of the test. That’s much more accurate than a Garmin which uses age norms. Devices may get more accurate as they collect more of your data but are least accurate when new.

BOOK A VO2 or ZONE TEST WITH TACTICAL DIETITIAN HERE 

A 2024 review found that fitness wearables overestimate VO2 max by about 15% on average. In the lab, if calibrated correctly and fitted properly, we can watch your VO2 plateau and get within a respectable range of your max. Many people are surprised that their zone 2 heart rate is higher in beats per minute when tested directly compared to age-based estimates.

Direct testing also tells me the story of your training: your current fitness, how you perform in each zone, how efficiently you use fat at lower intensities, how you handle carbs at higher intensities, and even what your recovery looks like. Even without knowing anything else about you, I can make strong assumptions about your fitness, nutrition, and training.

This data gives real insight for moving forward instead of just guessing. Checking VO2 and heart rate zones is a way to see how you’re progressing right now. It’s useful, but heart rate varies for many reasons - caffeine intake, stress, even weather changes. In the South, performance can decrease 7% just because of summer heat. That also drives up heart rate. Good trends to look for are your heart rate lowering in zones at the same pace, or you running faster while your heart rate stays the same or drops. People who do a lot of zone two training often have a wide heart rate spread in zone 2 - 20 or even 30 beats. Those who rarely train in zone two usually have a smaller spread and are less efficient at fat utilization, often going to carbs regardless of intensity.

RPE as an additional metric

So yes, heart rate zones matter, and testing matters. But there are days zone two may feel harder than usual. That’s why we should also consider RPE—how hard something feels—especially for tactical populations dealing with stress and poor sleep. Sometimes your zone two might feel like an RPE of 7 or 8.

How Calories are Inaccurate.

Another big question I got recently was about calorie counting. One client asked, why do people say a pound of fat is 3500 calories? There are 454 grams in a pound, 454 times nine is over 4000. It’s a great question.

The answer is that only about 85% of fat tissue is actually fat. The rest is water. Our cells, including fat cells, hold a lot of water. So we don’t count the water portion when calculating calories. That’s why fat calories are closer to 3500 per pound, not 4000.

So should we be counting calories or macros if they’re not accurate?

Yes, because it’s about trends and having a metric. Not every apple is exactly 100 calories and not every gram of carbs or protein is exactly four calories, but we need tracking mechanisms that are reliable and repeatable. For weight loss, calories and macros give structure and boundaries. For high performers at risk of underfueling, they provide minimums to prevent low carb or low calorie intake from hurting performance.

Even though none of it is 100% accurate, metrics give us a way to measure and make adjustments.

How Do I Increase VO2?

The last question came from a Reddit thread: how do you increase VO2?

You don’t train to increase VO2. VO2 is just a metric, a snapshot of where you are in time. It trends over time to help us understand your system and fitness. You should train for outcomes: running two miles in 15 minutes, finishing a marathon, hitting your fastest mile. VO2 is how we gauge progress toward those goals.

VO2 increases fast when you’re new to training but slows down as you approach your potential. Eventually it may plateau. That was the issue with the Reddit guy. Just doing zone two won’t keep raising VO2 forever. At some point you need power and speed work above threshold, then cycle back to endurance. Training is cyclic. Push one quality, then shift to another. Genetics also play a role, which is why even elite athletes sometimes have lower-than-expected VO2. Norms exist for age, gender, and occupation, but again it’s not absolute. Just a metric.

If you have thoughts, opinions, or arguments, drop them in the comments. And if you’re curious about VO2 testing, it’s more accessible now than ever. Just search “VO2 test near me” or, if you’re in the Columbus Fort Benning area, come see me and I’ll test you myself.

BOOK A VO2 or ZONE TEST WITH TACTICAL DIETITIAN HERE 

Thanks for stopping by!

References
 

1. Doherty C, Baldwin M, Keogh A, Caulfield B, Argent R. Keeping Pace with Wearables: A Living Umbrella Review of Systematic Reviews Evaluating the Accuracy of Consumer Wearable Technologies in Health Measurement. Sports Med. 2024;54(11):2907-2926. doi:10.1007/s40279-024-02077-2
2. https://www.army.mil/article/264267/fort_benning_conducts_2023_heat_forum