When it gets hot, it’s smart to switch to heart rate training

This article originally ran in spring of 2012.

As far as physical activity goes, running is the simplest one — but only at the beginning. Once you’re over the first painful phase of building up the stamina, once you’re able to run with ease and for a long time, once the first thought of running a race invades your mind — that’s when things get complicated. 

The most important decision you have to make is to choose a training plan. Your training can be based on distance, time, pace or heart rate. This last one is especially important for techie runners.

RELATED: What is resting heart rate and why should you monitor it?

While I don’t dispute the benefits of measuring the intensity of the workout based on heart-rate zones, I would like to point out some shortcomings of such training. But first, let’s remind ourselves what heart-rate training is.

Based on runner’s Maximum Heart Rate (MHR) and Resting Heart Rate (RHR), the training is divided across five heart-rate target zones:

1. The Fat Burning Zone — 50% to 60% of MHR — as the name says, training in this zone is ideal for drawing energy from fat cells by being low in intensity, but long in duration.

2. The Energy Efficient or Recovery Zone — 60% to 70% of MHR — training in this zone develops basic endurance and aerobic capacity, it’s ideal for recovery intervals.

3. The Aerobic Zone — 70% to 80% of MHR — training in this zone develops and improves cardiovascular system, especially the body’s ability to transport oxygen to the working muscles, and CO2 away from them.

4. The Anaerobic Zone — 80% to 90% of MHR — training in this zone will develop your lactic acid system: glycogen stored in the muscle is predominantly used as the source of energy, and a by-product of burning glycogen is lactic acid. A point at which the body can no longer remove the lactic acid from the working muscles is your anaerobic threshold. It is possible to train your body to delay the anaerobic threshold and increase the tolerance to lactic acid.

5. The Red Line Zone — 90% to 100% of MHR — training in this zone is possible only for short periods of time. It’s ideal for developing speed by working out fast twitching muscle fibers through sprint intervals.

To train by those intensity zones, you need a constant feedback on your heart rate, which you get by wearing a monitor. It consists of a belt-like strap which fastens around your chest and sends data to a display on your watch, or a smartphone.

I must confess: I don’t use the heart-rate monitor. I’ve tried it once and felt like an opera singer squeezed into a much too small corset. The hoop around the rib cage prevented my lungs from filling with air, and I couldn’t wait to take it off. But, some runners I know swear by it, listening to the beeps that tell them which zone they’re running through. Which finally brings me to point out what I think is wrong in all of the heart-monitoring strategies.

The whole concept of heart-rate zones is based on determining Maximum Heart Rate — which is as fast as your heart can beat. Without accurate MHR value, all the training zones become arbitrary. And before that, you need calculate the proper bpm value for each zone. A simple formula for that is: Target Heart Rate = [(Maximum Heart Rate – Resting Heart Rate) × %Intensity] + Resting Heart Rate

There are a myriad of formulas to calculate your MHR, but they are all based on average value. Since heart rate value is very individual, the MHR you get from a formula may wildly deviate from your real  heart rate. The most accurate way to find the MHR is through so-called graded exercise test, which could be costly even if you manage to find a facility that can provide it.

Further, many external factors can affect your heart rate: lack of sleep can raise the heart rate from 5 – 10 bpm (beats per minute); workplace stress will raise it by 4 – 6 bpm; caffeine elevates heart rate up to 24 hours after ingestion; hot and humid weather also causes heart to beat faster; dehydration can cause heart to beat 5 – 7% faster than normal.

All of these fluctuations in heart rate can cause your training to be seriously out of the zone you believe you’re training in. For example, since your Resting Heart Rate changes during the day, that also means your training zones change with it. So, if you don’t realize that your heart is beating faster than usual and re-calculate your training zones accordingly, you may believe you’re in the aerobic zone, while in reality you will already be hitting your anaerobic threshold in the higher zone. While such mistakes will only mean that you tire faster, in extreme cases you can overextend yourself by pushing too hard.

In conclusion: heart-rate training is a fantastic tool for elite athlete, because they have accurate measuring to start with, and specialists who can adjust their training zones based on daily fluctuations. Most of the rest of us don’t have resources to use it accurately. So, if you do train with heart rate zones, exercise caution and be aware of your heart’s fluctuations and the training’s limitations.