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RPE
Heart Rate
Power
RPE
RPE or rate of perceived exertion is a scale of discomfort used almost universally throughout the world for medicine and hospital functions, athletic training, and research. Its purpose is to objectify a person's discomfort levels by assigning a number to a level of pain where 10 is the most pain you can endure and 1 is no effort or discomfort at all. There are a few different RPE models but I prefer to use the simple 1-10 scale because it is the most ubiquitous, and easily understood, and most training programs like TrainingPeaks are designed to work with it.
Scale
Value | Perceived Exertion | Example |
1 | No discomfort or exertion whatsoever. | Sitting or laying down |
2 | Minimal exertion and no discomfort | Walking |
3 | Slightly more exertion but still no discomfort | Very light jog, easy endurance intensity |
4 | Entirely comfortable but conscience of the effort needed | Regular jogging pace, endurance intensity. Should be able to breathe through your nose at a normal pace without feeling like you're choking |
5 | Discomfort begins and conscience of the effort | Still able to speak mostly normally, but needing to take deeper breathes to do so; tempo |
6 | Uncomfortable but bearable | High tempo-low threshold intensity |
7 | Uncomfortable and requires concentration | Breathing begins to pick up and it is difficult to speak in full sentences |
8 | Painful and requires significant focus | Only able to speak a few words at a time; max aerobic intensity |
9 | Painful, nearly all out | Quick and deep breathing, unable to speak more than a few words at a time; anaerobic intensity |
10 | Very painful, as hard as you can go | Max exertion sprint, last bit of an all-out max effort |
Physiological Markers
An easy way to stay consistent with your RPE is to find something close to that intensity to anchor your thinking and focus to. This keeps you riding in the correct zone, and it gives you small things throughout the entire scale to look for so you can try and make your own personal RPE scale as consistent as possible.
RPE 3-4
This is generally the level you want to spend your time in when you are performing endurance rides to achieve the most benefit. A good reference to anchor yourself to here is when you get to 4, just before you go to 5, it should be at an intensity where you can breathe through your nose comfortably and normally. Many athletes think they can breathe through their nose at tempo intensities up in the 5-6 RPE range, but they are essentially hyperventilating.
If you can breathe in such a way that it takes about 2 seconds to breathe in and 1.5 seconds to breathe out (this is a breath rate of 17 breaths per minute, normal resting breathing rates are typically 12-17 breaths per minute) then you are most likely riding at an RPE of 4 and at the best intensity for endurance riding.
RPE 7
This is the point where you will reach your anaerobic threshold, or FTP/ threshold heart rate. You can note this point because your breathing will suddenly and drastically start to pick up, at an RPE of 8 your breathing will begin to feel out of control but a 7 is just about the limit of what you feel like you are in control of. You will be breathing deeply and quickly, but not hyperventilating. When you are doing productive threshold work, this is the intensity you want to spend your time at.
What Makes RPE So Important?
Productive training will have to push your body to the limits sometimes, but most times you need to stay composed and maintain a set intensity as precisely as possible. Having this intimate knowledge of how your body feels throughout a range of intensities is important for metering your intensity later down the road.
For example, you may know that once you get to an RPE of 8 you only have a few minutes before you are done and can't continue, so if you're going for a hard effort in a race, or going for a personal best, you will know that once you reach an 8 you'll need to back off slightly before you blow up entirely.
Similarly, you may be out for a long endurance ride and you are becoming fatigued, now the power/ heart rate you had planned that was originally a 3-4, now feeling like a 5-6. Having this knowledge and understanding of your own body will allow you to finish the ride without blowing up, maintain an intensity that is conducive to proper training, and keep you from accumulating so much fatigue you won't recover properly from it.
Heart Rate
Upgrading from just RPE to RPE and heart rate is possibly the biggest jump you can make in training accuracy and precision. It will make your training even more productive and specific, and give you access to new metrics to track your performance, recovery, and training as a whole.
Setting Your HR Zones
After you've spent some time in the zones above, it's time to perform a lactate threshold heart rate test to base your training intensity zones off. I prefer Joe Friel's method for a few reasons: max HR can change quite drastically throughout a training block due to fatigue, hydration, nutrition, stimulants, etc. but threshold heart rate will remain almost entirely unchanged as you get more fit, fatigued or use stimulants. Another reason I prefer this method is that it is based off an estimation of the location of your anaerobic threshold, so your zones are based on a physiological process rather than an arbitrary percentage of your maximum.
Performing a Threshold Heart Rate Test
Joe Friel suggests performing a 30-minute time trial and taking the average HR for the final 20 minutes and making that your threshold heart rate.
Make sure you warm up adequately for this test, I would recommend at least 20 minutes at roughly an easy endurance intensity, I also like to throw in an effort that is one or two minutes long at the intensity I intend to ride the test at. There are a few physiological reasons why this is important, but for less experienced athletes the shock it gives you mentally prepares you for the effort. Once you complete the test, the average heart rate for the final 20 minutes is your threshold heart rate.
Calculating Zones
I prefer the Joe Friel's Zones because it is specifically designed to be accurate at the anaerobic threshold, so it will be best at predicting intensities to work the metabolic processes involved in lactic acid production and clearance. Since the anaerobic threshold and the aerobic threshold are somewhat related to each other, I find these zones predict my aerobic threshold (endurance zone) very well too.
Why is Heart Rate an Important Training Metric
Although power is a more precise metric, I think heart rate may be the most important metric to look at when training, even if you have a power meter. As you get more fit, your threshold power will continue to increase but your threshold heart rate will not change much at all. This makes it easy to compare your performance against a relative intensity level that doesn't change.
Physiology
Heart rate is a Direct response to the metabolic processes occurring within the body. Through training, we are trying to precisely target those specific processes in such a way that they get stronger or more efficient.
Changes to VO2 max are made most effectively at very high heart rates, not necessarily power outputs. If you are hitting your power targets for a VO2 workout but you are too fatigued your zones are set so that your heart rate never gets above 90-95% of your maximum, you are missing out on gains.
Data Tracking
As you are slowly getting stronger over time, your heart rate will be lower than it once was at a similar power. If you don't test your FTP and regularly correct your power zones, you could be stressing the wrong processes and not training as effectively as possible. By incorporating heart rate into your training tools, you can compare it to your power over time and make educated decisions on your fatigue and fitness.
Similarly, you can use this ratio of power and heart rate to track changes in your general aerobic fitness over months or seasons. If your heart rate and RPE is slowly going down at the same power (or power goes up for the same heart rate and RPE) you can make an assumption that your endurance fitness is increasing without necessarily needing to directly test it. It is still a good idea to perform fitness tests from time to time to track these performance changes more concretely.
Power
Power has become the gold standard tool for tracking and prescribing changes in fitness in cyclists. It offers much more precision, accuracy, and second by second data collection. Power records your body's output while heart rate is the cardiovascular input required to produce said output. RPE is what you psychologically perceive the interval workload (input) as. So power differs from the two other metrics simply because it measures output instead of input.
Another useful aspect of power over heart rate is its ability to record instantaneous changes in intensity. Heart rate "lags" behind the effort, so a 20-second maximum sprint might only show an elevated heart rate for the final 5-10 seconds of the effort, and the heart rate will continue to be elevated after the effort is completed. Power will show you the intensity the instant you begin to apply force to the pedals and will go back down the instant you stop applying that force.
Setting Your Power Zones
Heart rate zones don't change frequently or by much, so you don't need to re-test them much at all. Power and your FTP, on the other hand, is a much more dynamic and volatile metric that should be tested in some capacity relatively frequently. This doesn't necessarily mean you need to do a formal power test every month, but it is not a bad idea to test a variety of power ranges throughout your training from time to time to see where your relative weaknesses and strengths are, as well as making sure your training zones are set correctly.
Below are a handful of well-established power testing methods that you can use in your training.
Power Testing
The 20-Minute Gold Standard
The most popular FTP test there is the 20-minute all-out time trial. If you have trained with a power meter for any period, you have probably done this test. You ride as hard as you can for 20 minutes, then you take 95% of whatever that power was and that is your FTP.
This is the first mistake riders make with this testing method, it isn't just riding as hard as you can for 20 minutes. The official protocol is to also do an all-out 5-minute effort just before the 20-minute test to try and minimize the contribution from your higher power-producing but less efficient muscle fibers. If you have ever done a 20-minute test without the prior 5-minute effort, you may have noticed that the first 5-ish minutes feel fairly comfortable despite your power being high, but soon your power starts to drop. This higher power at the start is you utilizing these muscle fibers and once they become fatigued they can not produce that power anymore so you are left with just your weaker, aerobic fibers to do the work.
Incorporating the max 5-minute effort at the start will minimize the contributions from these anaerobic muscle fibers and leave you with a more accurate representation of your aerobic fitness. That is the goal of FTP after all, to measure your maximum aerobic fitness without significant contributions from the anaerobic system.
The 2 x 8-Minute Test
A less common FTP testing method is the 2 x 8-minute test developed by Carmichael Training Systems. This test is simply an 8-minute all-out effort followed by a 10-minute recovery period and a second all-out 8-minute effort. This test calculates FTP as 90% of whatever the highest average 8-minute effort was.
This test is likely to overestimate your FTP and CTS clearly states this as a con of this testing method. Since this test takes the highest average power and not always the second effort's power, there is no way to minimize the contribution from the more anaerobic muscle fibers. You are more likely to produce higher power on the first effort since all of those muscle fibers are warmed up, not fatigued, and ready to go.
With this test being shorter in duration and not having a method to pre-exhaust the anaerobic muscle fibers, the results from this test will include a significant amount of anaerobic contribution. This contribution will likely lead to a higher calculated FTP than in reality, especially if you are a rider who has a higher proportion of those muscle fibers.
The Ramp Test
There are a handful of different ramp test protocols but I will be referring to the 20-watt/ minute one that can be found on Zwift. This test is arguably the most popular one out there because of Zwift, but many physiology labs use different power increases and step durations based on the specific goals of the test. This is a graded exercise test meaning you increase the intensity by a set amount (20 watts) after a certain amount of time (1 minute) until you can not go any longer. The FTP calculation for this test is a bit more complex:
MAP = (power of last completed stage) + ((% of uncompleted stage / 100) * (power of uncompleted stage))
FTP = MAP * 0.75
This test has the advantage that it requires no pacing strategy, so you can get an accurate result on your first test, and subsequent tests don't improve by simply getting better at the test. It also has the advantage that it is so short and only hard for such a small amount of time, you could realistically do this test before a set of intervals or regularly throughout a training block without risking overtraining, the same can not be said for the other two tests. However, because of how short this test is and the fact that it goes to absolute failure through the anaerobic intensity ranges, there will be significant anaerobic contributions which could lead to an overestimated FTP.
Calculating Your Power Zones
I like using Duration Training's power zones because of the descriptive names for each zone and how closely they tend to correlate to the Friel heart rate zones.
Why Train With Power?
I like using heart rate because you can use it to measure the direct metabolic responses in the body, but power allows you to measure the performance and efficiency of those metabolic processes.
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