Using heart rate and power: how do they relate?

True or False, do you think that heart rate is important while training?

The answer is “True”, and you would be amazed at how many riders focus only on wattage and neglect the thing that keeps us moving.

If you really want to balance out your training adding in a heart rate component is important, but it can be confusing. Where riders get confused is understanding how your power and heart rate zones relate to one another, and which should take precedence.

Your zones may not align

Let’s be clear, it is normal that your power and heart rate zones may not align. What does that mean? You may find that when working in a particular power zone, let’s say you are doing a tempo ride, that you struggle to ride in the same heart rate zone. What typically happens is that when you push tempo wattage you can ride at the tempo heart rate zone for a bit. But slowly your heart rate will increase and next thing you know you are riding at your threshold heart rate.

Why can’t you ride at your tempo power and have your heart rate in the same zone?

One reason is the underdevelopment of your aerobic system. The better your aerobic system - think endurance and tempo training - the more your zones will come into alignment. If all of your training has been threshold oriented, and by power, you have likely not developed mitochondrial density in the muscles, which supports aerobic work. Mitochondrial density quite simply means making lots of healthy mitochondria, which are “the powerhouse of the cell”. Creating this mitochondrial density is one of the goals of proper aerobic training.

The second possibility is perhaps the quality of your respiration, an area in which many cyclists struggle. The concept of improving your breathing is part of our Tool Box. The better your breathing the lower your heart rate will be: Don’t forget to breathe well.

Is power or heart rate more important?

Deciding on whether to follow power or heart rate to guide your workouts depends on the type of workout. The more aerobic the workout - endurance and tempo - the more you should rely on heart rate. The harder the workout - threshold and VO2 - the more power becomes the target.

Using heart rate for our aerobic work will ensure that it is done at the appropriate level - that it isn’t too hard.

Think of those tempo workouts where you apply a heart rate ceiling and you experience your power falling across the workout. We are using the heart rate as a guide, to ensure the workout remains a tempo workout and doesn’t turn into a threshold or even a VO2 day.

Power can then be used as a carrot to motivate us on the days when it is time to go hard. Keep in mind that the heart rate does take a bit of time to respond to your efforts. Higher wattage workouts tend to be made up of shorter efforts where power is a better gauge of your work.

“Adhering to proper heart rate zones will make more significant performance gains and increase metabolic efficiency across all systems. Going slow or taking easy days will enhance one’s ability to go hard on others. Improving low-end anaerobic energy as well as high-end intensive energy will make the body efficient at burning fats and carbohydrates during exercise and also at rest”, from “The Lactate Revolution” by Shannon Grady.

We all want to train harder, and you may be frustrated at first when having to back off your power to stay in a heart rate zone. Give your systems some time to develop and you will find your ability to sustain the power getting better. Combining power and heart rate zones will be the best way to become a better cyclist.