I remember my first heart rate monitor. A Polar S720i. It used infrared to download data. Infrared! The first time I wore it, it felt like magic. The device was a key to unlock secrets about my body I could have never observed before. I wore it when I exercised, I wore it all day, I wore it all night for the first week. Of course I knew my average heart rate for actives like cycling and running, but I knew it even for mundane activities like doing the dishes (61 bpm).

Since the first commercial heart rate monitors were introduced in 1982, using heart rate to monitor intensity remains the method of choice for the plurality of recreational athletes. Of all our 80/20 plans use sold in the past year, 41 percent choose a heart rate-based plan, with the remaining 59 percent almost evenly split between pace and power. Why does heart rate remain so popular after 36 years, even with the advent of more sophisticated technology? Because heart rate training is cheap and easy. It is the original “plug-and-play” device, with reliable and simple setup, and at a cost often less than 10% of power meters.

But that 41 percent is declining. We estimate that pace and power sales will each eclipse heart rate training by the end of 2019. As the cost of pace and power devices comes down, athletes have already begun to shift to these alternatives. But it’s not just cost that drives this decision. Athletes increasingly recognize that despite the advantages of heart rate training, it has significant drawbacks. The most glaring drawbacks being reliability and consistency.

To illustrate this, think of measuring exercise intensity like you do with your car, and imagine that in addition to the various gauges on your dashboard your car has a gauge measuring horsepower. Your car’s horsepower is an output, the speed is an outcome, and the engine temperature is an indicator. These measurements line up with using power, pace and heart rate, respectively, to measure intensity when training. Engine temperature (heart rate) does not actually represent any output or outcome. It is simply an indicator of how the car is responding to the input and environment. Your car’s engine temperature needle can be through the roof when idling at a stoplight in summer, or resting near the bottom when driving at 50 mph on a cold day (Honest, officer! I wasn’t speeding! My engine temperature was super low).

Likewise, your heart rate will respond very differently based on environmental conditions, even when the output is identical. For example, an athlete running on a treadmill set to 14kph at a room temperature of 70 degrees F may have a bpm of 160, but a bpm of 180 if the room temperature is increased to 90 degrees F. The output is the same at 14kph, but the data on the indicator is much different.

Temperature is only one factor that can influence heart rate. Evening workouts have a bpm 4 beats higher than the same output during a morning workout. When and how much you last ate can increase hear rate by up to 10 bpm when exercising. Sleep and stress can cause wild fluctuation in heart rate. Indoor training training tends to be 5 to 10 beats lower than the same output for outdoor training. It is these, and other factors that make heart rate training less reliable and less consistent than power or pace.

Contrast that to using power as a measure of intensity. A watt is a watt, regardless of temperature, time of day, or stress. Pace also has drawbacks, but is reliable when performed on a relatively flat surface. And for most of us, isn’t the outcome (pace) the whole point when racing? There are no awards for highest heart rate in a race, it goes to the individual with the best pace.

But I’m not here to bury heart rate, I’m here to praise it. Despite the drawbacks, heart rate can play an important role as a secondary measure when training and racing. Using pace in hills is foolish, but having heart rate in your toolkit can help you find an appropriate pace. A watt may be a watt, but heart rate is indeed a key to unlock secrets about how your body is responding to the stress of training and racing. It may be that heart rate is the angel on your shoulder telling you to slow down when pace and power devils are telling you that you’re just fine. A combination of monitoring pace plus heart rate or power plus heart rate will always be superior than relying on any single measurement.

Heart rate monitoring may be losing popularity, but it isn’t dead. It isn’t even dying. I’ll be the first to recommend power and pace as primary measures of intensity, but I haven’t done a workout or race without a heart rate monitor as well in years.

Besides, there will never be a pace and power intensity measure for doing dishes.

If you already have an 80/20 plan that uses heart rate and want to try pace or power, we offer a free switch to any other measure of intensity or level within your purchased plan distance. Contact us and we’ll make that happen.