While power meters have become very popular for cyclists, and are extremely useful as a training tool, there are still many athletes who don’t have that equipment. This is just fine if we have a solid grasp of how heart rate works in the context of exercise. In fact, I’ve coached multiple masters athletes to state and national championships using heart rate and perceived exertion to direct our training sessions. Allow me to explain the how’s and why’s of using heart rate for training.
Setting the Stage
Let's start right off the bat by doing away with some outdated and potentially confusing ideas around heart rate. First, it is incorrect and misleading to calculate your heart rate (maximum or threshold) based on any formula that uses age or gender to arrive at your maximum or threshold heart rate (Max HR = 220 – Your Age). It’s amazing that these formulas still persist, as exercise scientists have known better for decades now. Put simply, there is a wide range of heart sizes among athletes. This is natural and has no determination on athletic performance. A larger heart will simply pump more blood volume with each contraction, which means it has to pump fewer times per minute to deliver the same amount of blood as a smaller heart. I coach athletes who have threshold heart rates in the 140’s and others of the same performance level who have a threshold in the low-190’s. These athletes could be twins, save for their heart rates. More on threshold and its importance in a moment.
The next thing we need to do is shift our focus away from maximum heart rate. This is both for generating training zones and for any concerns about performance. For many athletes, their ‘maximum’ heart rate is only the highest they’ve seen and is actually nowhere close to how potentially high it could go. I feel that max HR is irrelevant for most athletes, as it can only be reached at the absolute ragged limit of their abilities and only under the right conditions. It’s not something we use for training and it has essentially no bearing on performance. As a professional athlete with over 20 years of racing and training, I only reach near my maximum heart rate a handful of times each year – that’s amongst hundreds of hours or training and racing each season. And that’s with a racing focus on shorter, super high-intensity events. For the majority of athletes, training zones calculated from maximum HR will most likely be low, unless they have truly gone all the way to the end of the red zone. Put simply, don’t give maximum HR a moment’s concern.
Threshold Heart Rate
So if we don’t worry about maximum, how do we know where to train? The answer lies in our functional threshold heart rate. For many years this has been incorrectly referred to as ‘anaerobic threshold’. This is misleading, because there is never a switch-flip moment where the body simply ‘goes anaerobic’. Instead of switches, think of our energy systems as series of sliders. At low intensities, most of our power production comes from our slow-twitch muscle fibers which are fueled aerobically (using oxygen). As we push the effort higher, we need more power than the slow-twitch fibers can create on their own, so our fast-twitch (high force) muscle fibers begin to be engaged. These muscle fibers are predominantly fueled anaerobically (without oxygen) and burn almost exclusively carbohydrates.
The simplest way to think about our functional threshold is the highest output we could sustain for one hour. I’m talking about a falling-off-your-bike at the end kind of time-trial effort. This means we have near maximum aerobic power production along with a heavy contribution from our anaerobic energy systems. While there is nothing magical happening in the body at this level of power production, it is a very useful output level to benchmark. Using this level, we’re able to generate our training zones, both for power and for heart rate. For this article we’ll show power zones for reference, but focus on heart rate.
The one-hour maximum output affair I mentioned above can be a rather unpleasant undertaking, especially outside of a race setting. Luckily, there’s a shorter test we can do to determine functional threshold HR. This will be most accurate when done well rested, as fatigue will often lead to lower heart rates for the same effort. Try to keep the conditions similar to a normal exercise session (no excess caffeine, stress, etc). The test is as follows:
Begin with a 15-20 minute warmup. We want to gently ramp things up and make sure to include a few 30-60 second hard efforts to blow out the jets.
Ride easy for a few minutes.
Complete a 30-minute effort time-trial effort. We want the highest power output that’s sustainable for the entire 30 minutes. Hint: Most people start too hard. Be a bit conservative and know that it’s better to ramp up than to blow up partway through. This should be done on a generally flat road, free from traffic or intersections. It can also be done on a trainer.
At the 10-minute mark, if you can, hit the lap button on your watch/computer.
The average heart rate for those final 20 minutes is our approximate threshold HR.
Once we have our own unique threshold heart rate, we can calculate our zones. I personally use the zones developed by Andy Coggan. There are others other there that have smaller ranges and more zones, but that granularity is not necessary. The zones I use with my athletes are shown below along with a description for each. Note, the scale of perceived exertion I use with my athletes (shown below) differs from Coggan's.
Considerations for HR-Based Training
It’s important to know that heart rate is not a direct measure of output, like power, speed or pace. This is a measurement of what our heart is doing in order to keep many systems in our body operating. One example of this occurs during hot weather. During exercise, most of the heart’s role is in supplying much-needed oxygenated and fuel-rich blood to our muscles, along with transporting metabolic byproducts and CO2 away from the muscles. However, we are only about 25% efficient in turning this fuel into muscular power. The other 75% is converted into heat. This must also be transported by the blood to our skin for cooling. What occurs is an increased heart rate in an attempt to keep the muscles supplied while pumping blood to the capillaries in our skin. As we get hotter or dehydrated, this effect only increases. This means for the same output (power/speed/pace) our heart rate will climb.
I bring up the example above to highlight that heart rate, while a useful training metric, is variable and cannot be held as tightly as metrics such as power. Other things that can cause HR to be higher or lower are sleep, fatigue, hormone levels, caffeine, dehydration and stress. So keep this in mind and don’t fret if your HR values seem to be a little high or low for the same effort. One thing that heart rate is very useful for is monitoring fatigue. If your HR is very low and sluggish, even after a solid 20-30 minute warmup, that may be an indicator of fatigue and a sign it’s not a good day to go hard in training.
I hope this helped to build your understand of heart rate and its use in training. Please feel free to reach out with questions or with other topics you’d like to see explained. You can contact me here.