Heart Rate Training, Explained

There’s been quite a bit of chatter lately about heart rate training. What is it? What does it mean? What good does it do? I’ve spent a lot of time talking to people about how it works and why it’s important, but explaining it in a thread of Facebook comments is somewhat cumbersome and I think it’s worth diving into further. So here we go.

When I first started running, like most new runners, I was entirely focused on pace. I wanted to be fast, so I ran fast. As fast as I could, all the time. Every run ended the same way. Me, in a pile of exhausted, panting in the living room floor. Pooped. Kinda feeling sick. Must take a nap. Now.

What I didn’t realize was, I was shortchanging myself. I was running too fast. Yes, you can run too fast.

Let me explain.

Two process help our bodies bring necessary fuel to our muscles during exercise: aerobic metabolism and anaerobic metabolism. Though they never work exclusively, one will always dominate depending on the intensity of exercise. The less intense aerobic process uses oxygen to turn fat into fuel and the more intense anaerobic process converts stored glycogen (sugar) into energy in the absence of oxygen.

Confused? Stay with me.

When you run slowly, you’re not working hard; your heart rate is low and breathing is slow. Your body is burning mostly fat. Fat metabolism is an oxaditive process – meaning your body needs oxygen to turn your fat stores into usable energy. If your heart rate is low, and your breathing is controlled, you are providing your body plenty of oxygen to burn your fat.

The faster your move the more your fat metabolism revvs up and the more oxygen your body demands. As soon as your body demands more oxygen than you can effectively deliver (a.k.a. you start breathing hard or panting), an oxygen defect is created and your body starts looking for an alternative source of fuel that doesn’t require oxygen for metabolism- enter glycogen (sugar).

If fat is your gas tank. Sugar is your nitrous oxide boost.

The heart rate in which your body switches from primarily fat burning to sugar burning is called your lactate threshold.

As long as you stay in that happy, I’m-not-panting zone your exercise is self-sustaining and you can almost run forever off stored fat. But with only 2,000 calories of glycogen (sugar) available, there’s really not that much there. Wanna know why marathoners hit the wall? They’re exceeding their body’s ability to burn fat and they run out of sugar. That’s it.

Got it? Good.

But what does that have to do with running too fast?

You can manipulate how your body burns fat and sugar by how fast you run during training. Your body adapts to the stress placed on it. Which means, the more you stress your body in the oxygen demanding, fat burning, slow, I-love-running, happy zone, the more efficient your body becomes at delivering oxygen to your muscles and burning fat.

How does it become more efficient? Inside, you grow more capillaries to deliver available oxygen to muscle cells and you produce more mitochondria which use that oxygen to turn fat into fuel. You’re literally growing new body parts. Pretty cool, huh?

This is aerobic development. And guess what? You don’t grow body parts overnight. Aerobic development is a slow process which takes WEEKS, MONTHS and even YEARS.

Run a lot. Run slower. Become more efficient. Be patient. Get faster. It’s an easy process that pays off.

What is the secret formula for determining the ideal heart rate for training?

If you’re an advanced athlete, getting a VO2 max test done will be beneficial. Use the results and stay at the top end of zone 2 – but most recreational athletes can get by with using an age based formula.

180- your age with the following modifications:

-10, if you’re recovering from major illness or are on regular medication, or you’ve never exercised before
-5, if you are coming back from a layoff, or workout 1-2 times per week
+/-0, if you work out 3-4 times per week
+5, if you’ve been running injury free for at least 2 years and/or work out 5+ times per week, or are older than 60/younger than 20

In case you’re wondering, I’ve not had a VO2 max test done and am training with the 180-age formula. I’m 38 years old and I add 5 because I run a gazillion times a week.


142+5=147 is my target.

I’ve spent the past 15 months running at a heart rate of slightly less than 147, with the exception of a handful of speed sessions leading up to Boston, and it’s paying off, in spades.

Wanna see the proof?

This was my first heart rate based run (see image below), April 20, 2016. I had qualified for Boston only three months earlier; I was in the best shape of my life. I thought I was the sh!t. I was served a big fat piece of humble pie on a giant silver platter.

Average heart rate 145. Average pace 10:30/mile. Chew on that. Ugh. Maybe I wasn’t in as good of shape as I thought.

Notice the peaks and valleys in the heart rate as I struggled to keep it under control? Just a slight change in pace caused a significant increase in heart rate as my body teetered on the edge of being able to deliver enough oxygen to my muscles.

Fast forward a year and three months. This run was July 20, 2017 (see image below). Average heart rate 142. Average pace 9:10/mile. The cool part is, this includes my warm up. The further into the run I got, the faster I could go as my heart got in sync with what I was asking it to do. By the time my body was moving efficiently at mile 3, I was at an 8:13. For me, that’s sub-BQ pace, at a heart rate of 147. Pretty freggin’ cool.

Notice how steady my heart rate is? My body isn’t struggling to deliver oxygen. My heart is easily able to keep up with the oxygen demand as I slowly increase my pace.

Both runs are public on Garmin Connect if you’d like to click the links and look at the data.

What does it boil down to? The aerobic base is secret speed training.

Think about it this way. Everyone has a maximum heart rate which doesn’t really change except with age. So, if my heart is beating at 145 bpm at a 10:30 and my max heart rate is a 185, by the time I get down to an 8:00/mile I’m thinking OMG-I’m-going-to-die! BUT if at the same heart rate I’m running an 8:15 instead, my OMG pace is closer to a 6:30/mile. All of a sudden my performance is no longer limited by my heart, it’s limited by my legs.


This aerobic base is the key to running fast over time. Though speed work has its place in training – its effects are lost more quickly once de-training begins. Aerobic development, however isn’t lost so easily, so you don’t loose quite as much speed between training cycles. And when it’s time to train for a race you can do significantly less speed work.

What’s more, the slower pace is less stressful on your body, allowing your body to naturally build up it’s smaller stabilizing muscles as your pace increases over time and lowering your chances of overuse injury. So next time you’re tempted to up the pace of your run remember, you have to run slow before you can run fast! Slow down!

UPDATE: I wrote this article in mid-July and I’ve since had a VO2 Max test done (9/14/17). Since I have not yet been able to use the results of the test in training, I am refraining from including any of that information in this post. I will write a separate post about the test itself and the results.

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