The methods cyclists use to get faster have evolved since the late 1990’s. Twenty years ago, if you were using a power meter you were considered an early adopter. Now, power — whether you’re using a power meter or another source — is the gold standard that modern athletes use to measure their fitness and performances.
Why Use Power Over Heart Rate?
With power, the numbers don’t lie. Power-measuring devices — most commonly power meters and smart trainers — objectively measure what it takes for the body to turn the pedals over at any given effort, instantaneously.
Unlike heart rate, power is a consistent measure of the energy being applied to the pedals. This tells us a lot about the tolls taken on the physiological processes of the body during training and racing. The advantage here is that cyclists are able to isolate particular areas of their training for specific performance improvements that previously weren’t as accurately understood.
Quantified in watts, a measure of a cyclist’s power is consistently calculated using an internal component within a power meter known as a strain gauge. Each of these devices are precisely calibrated by manufacturers to ensure consistency across the board. Specifically, within each power-measuring device the calculation for power goes something like this:
“Using power as the primary metric to train and race with allows cyclists to isolate particular areas of their training for specific performance improvements that previously weren’t as accurately understood.”
Lagging Indicator of Strain vs. Instantaneous Indicator of Effort
One of the greatest advantages power has over heart rate is that your efforts (or lack thereof) are immediately and accurately represented. Measuring cycling efforts using heart rate is a lagging indicator of how an effort is straining the body. Increasingly evident in shorter durations efforts, you can see in the figure above how responsive power (yellow) is to an effort compared to heart rate (red). As opposed to the yellow line for power, heart rate takes a few moments to begin to level off at that same effort level. You will also see the red line for heart rate mislead you in thinking you’re working after the interval has already been completed as the prescribed effort lowers in the recovery valleys.
Steep climbs, gusty winds, varied terrain, in each circumstance power numbers will always be true. Judging efforts in these conditions using heart rate could tell you otherwise. Potentially its achilles heel, heart rate is also largely affected by a large number of external variables.
This underlying issue behind obtaining consistent heart rate readings disqualifies any heart rate-derived metric (trend analysis like Max HR, Heart Rate Decoupling, Resting Heart Rate) as being reliable.
“Power objectively measures the amount of work you’re doing. Although heart rate is objective in that it measure BPM, it is completely subjective in terms of the physiological stress being put on the body.”
What Happened to Heart Rate?
Cyclists have always known and accepted the variability of using heart rate as a measure of effort. At one point in time, it was our only choice. We have known of the many factors that work against gaining repeatable results from heart rate, including:
– Race nerves
– Level of fatigue
– Riding at different elevations
– Fluctuating stress
– Level of hydration
– Nutrition
– Caffeine intake
– Position on the bike
– Level of recovery
– Lingering illness
– The list goes on …
Like advances in any field — science, education, engineering — when new technology provides an improved substitute, you accept change and learn to adapt. This is the transition that modern athletes made: moving from training and racing by heart rate to doing so using power.
This isn’t to say readings from a heart rate monitor are false data. Heart rate monitors objectively measure how many beats per minute an athlete’s heart is beating. What modern athletes training and racing with power argue is there are too many variables that can impact why it’s beating that many times per minute. It is objective in that it measures BPM, but it is completely subjective in terms of physiological stress being put on the body.
How The Modern Athlete Uses Power and Heart Rate
Athletes wise to contemporary training methods use power-measuring devices as their primary training tools. These athletes may also use a device that measures their heart rate alongside power, as a secondary metric. The key thing here is they use heart rate as a complement to their power data as a way to tell a more broad story about their training, rather than using it as a sole guiding metric.
This goes to show you don’t have to throw your heart rate monitor away — we’re certainly not advocating that. Instead, what’s required is a shift in focus. That’s it. Because as all modern athletes know, focusing on the right training tools in your search for speed can make all the difference.
For more cycling training knowledge, listen to Ask a Cycling Coach — the only podcast dedicated to making you a faster cyclist. New episodes are released weekly.
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For lower power more sustained interval efforts at recovery, tempo and maybe even sweet spot where one is sustaining an effort for 20 mins to an hour or longer, personally I find HR really useful. During the base training phase it’s surely important to know that the intensity is correct as fitness will be changing. Training peaks offer metrics such as ‘decoupling’ which might indicate an effort is too hard if there is HR drift when power is fixed. For my sweep spot intervals, where I will be aiming to push the power up to 90-93% of my FTP, I use HR response to judge what power level is right for me as the weeks go by. For recovery rides I’ll limit power but also have HR limits set, as primarily one is presumably trying to limit physiological stress and as you say in the blog piece the body responds to power demands in a variable manner.
Back in the day, we trained based on perceived effort. Heart rate was used to establish whether the perceived effort was correct. It’s not like we’d go really hard at the beginning of a session because our heart rate was low. We’d go at a perceived effort we though would generate the desired training stress and check the heart rate toward the end to verify we achieved it.
I use HR alongside along with Power. If my HR is way too high for the power I’m generating in an interval or I can’t get my HR up I just forget about the session and do a recovery ride or have a rest day instead
I just sold my HR strape. I don’t look at it while training/racing only afterwards and don’t do anything with it so why bother.
Why you want to use HR is to keep tabs on things such as Decoupling and PW:HR stats among other reasons.
Ed, sure. Only it’s another metric to track. I know about decoupling and PW:HR but I don’t do anything with it. Next is tracking room temperature and see how my power related? It’s a fact, I don’t handle based on the results from those metrics.
For me it distracts me. When TR comes with the option to switch off HR, but still record it, I might use it again.
Power meter won’t tell you that you swam way way too hard at the start of an ironman and you’re overdoing what you can handle on the bike and you’re going to end up walking the marathon.
It’ll tell you that you’re doing 250 watts sure, but how is your body handling it?
Yes, i understand the issues with heart rate and training, but there is still valuable information there, especially for long course athletes.
See why some pros like Andrew Starykowicz continue to train by power, but race by heart race.
Also could look into research by Alan Couzens and power:heart rate Efficiency Factors
The knock on HR is always that it’s subjective – however that is why it’s important. The subjective factors effect your training and racing. The power number only tells you what your legs are doing without regard for the entire system. I think this article, along with most proponents of power, discount heart rate as a useful metric way too much.
As an example lets say my training indicates I should be at about 200 watts over the course of a 40k bike leg at my next Oly tri. The night before the race I don’t sleep well, on race day the water is choppy resulting in a harder and longer swim, it’s very hot outside, etc. The effects of all these subjective factors are not going to show up on my power meter. I can use a combination of my power meter and RPE and/or HR to establish proper pacing, but not the power meter alone. Simply holding to my 200 watts will likely result in a very bad day.
I train with power, keeping an eye on HR and RPE, but race primarily off HR. The HR does not adjust up and down as fast as power obviously, but for triathlon, which is primarily a steady effort on the bike, HR rules on race day.
HRV is a perfect example of how heart rate information can be used as an indicator of trainging impact. This podcast goes into how top athletic programs use it to assess training load.
https://elitehrv.com/pillars-athlete-monitoring-don-moxley
There are a couple of good programs for doing this Elite HRV and HR4Training (this one uses your phone’s camera as the sensor).
Thanks so much for sharing, we’ll check it out 🙂
Great video and article. I am newer to power based training and have been working with heart rate and RPE over the last 3 years. It’s definitely a both-and (rather than either or) situation for me. I have used HR a lot to pace on big rides / events I am riding in, usually keeping it in the endurance to tempo range first half, then tempo and above second half and have found this pretty reliable. I have often found though that I can actually hold higher HR than I am used to in training on event day so have learned to trust how I feel overall as well.
I think for interval workouts power is a no brainer and I am loving what TR is doing for me in that regard. I do notice a big difference in heart rate related to temperature when I am doing TR workouts i.e. lot’s of drift (vs power) if I am not cool enough and pretty much parallel when I am cool (for stuff up to FTP). I also use resting heart rate and HRV (using Sweet Beat HRV app) to track recovery and find this very useful, and I am starting to track Power:HR efficiency as an overall fitness metric which is also helpful.
I just love to geek out on all this stuff and learn through experience how it all inter-relates.
Great Video, of modern athletes training. Love the article too. Check out one of my Athletic Courage site
https://athleticcourage.com/. Hope this will help other athletes as well
The HR is essentially more than just “how many beats per minute an athlete’s heart is beating”. The HR reflects the real mood and condition of an athlete, all these factor mentioned above involved in HR. Here is example that use HR monitor as a prime tool alongside power metric:
let’s say your FTP rate is 300 Watt at 170 HR lactate rate.
Suppose next input data:
1) You have the goal competition, therefore you have a race nerves;
2) the last week was full of stress due to overstress at your work – Fluctuating stress; 3) the last week was very hot and dry, so your Level of hydration is low.
All these factors affect the level of current condition, so at your 170 HR lactate rate you can produce 270 Watt.
And here is a point, you know that your FTP is 300 Watt but actually under these condition your real FTP is 270 Watt, therefore you push one hour race at your 300 Watt power and you shortly after 15-20 minutes of the race will find yourself in oxygen debt and you will be in real trouble.
Conclusion: The HRB is you, the Power meter rate is exogenous constant measurements.
Hey Denis,
You’re right that your heart rate can offer you insights into your overall condition. However, it’s impossible to make a 1-to-1 connection from heart rate to performance. This is why we prefer power as an objective measurement of actual capability. Combined with a personal awareness of how you feel and potentially with other metrics like heart rate, power offers by far the best way to train, pace, and monitor progress.