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  Latest update: 12/15/2023

Heart Rate Monitors, Watt Meters, and Biosensors versus Perceived Exertion (PE)

How hard am I working? Am I pushing myself and getting the maximum from my training efforts? These are common questions for those focused on a high quality workout. Although Heart Rate Monitors and watt meters are touted as the ideal tool to adjust the intensity of a training ride or dial in a level of exertion for longer endurance rides, there is a cheaper, easier (and in some ways better) alternative - using the Rating of Perceived Exertion (RPE or PE) scale proposed by G. A. Borg in 1982.

Perceived exertion was used by Lance Armstrong in his 55-km (34-mile) time trial victory for his 6th Tour de France. From an interview with Phil Liggett and Paul Sherwen. "I didn't have a speedometer. I said I'm not looking at speed, I'm not looking at cadence. I'm just going to ride like I feel."

And it worked. He won the stage convincingly, taking 61 seconds out of time-trial rival Jan Ullrich. "Going naked" in a TT seemed an unusual strategy for Armstrong who, prompted by coach Chris Carmichael, is an extremely scientific cyclist. Lance used a watt meter on most rides and sent Chris the files to download and analyze to plan subsequent workouts. Lance could have ridden the TT with a watt meter to monitor intensity and avoid crossing his red line, yet the only feedback he chose to use was his perception of his level of exertion. Like many experienced time trialists, he has a keen sense of pace. He has learned to tread the border between going too slow and losing time and going too hard early and slowing dramatically in the final kilometers.

And here's another example from "In a recent interview with VeloNews, 2004 Paris-Roubaix winner Magnus Backstedt commented on how his training changed after several years of poor results. 'I got back to what I did when I started racing', said the 30-year-old Swede. '[I had been] doing all kinds of controlled training, hitting thresholds, intervals, all that. Instead, I went back to what my body told me. I took every single piece of equipment off my bike. At the end of the day, despite what technology tells you, if it's not right, it's not right. It's been fine ever since.'"

Backstedt's comments have provoked lively exchanges in internet discussion groups on training. Some applaud his return to more "natural" workouts. Others deplore his flight from analysis and scientific training using watt meters and heart monitors. Which approach works best? I like the way Allen Lim, Ph.D., coaches his riders. In his ground-breaking doctoral work at the University of Colorado, Lim analyzed data from power meters used by pro riders in races and training. You'd think he would advocate scientific training. He does, but recommends training by feel and ONLY THEN analyzing the results by scientific means.

Structured training plans are important to meet cycling goals. But as Lim and Backstedt point out, the plan needs to be flexible. If your training plan calls for hard intervals, climbing or long distance on a certain day and your body isn't cooperating, it's crucial to recognize that you're not ready for more work and should change course to a combination of less strenuous workouts and more rest instead of blindly soldiering on and digging yourself into an even deeper hole.

The key to aerobic improvement will be a combination of perceived exertion and interval training. For the intervals (sprints) your will just work as hard as you can push - your maximum perceived exertion. But to train for longer than just 30 second sprints, you will ride at your LT or lactate threshold (LT). To do this with PE, first identify your maximum heart rate using a HRM, then ride for 20 or 30 minutes at 90% of that maximum heart rate (which should also be your LT). Note how your body feels - legs, breathing. Then get rid of the HRM and ride at that level of perceived exertion for your LT rides. You are no longer chasing the numbers of a HRM. A much saner way to match the variability in how your body feels from day to day.


Before commenting on the use of PE versus hard data from a HRM or Watt Meter, a few comments on two of the new biosensors for glucose and lactic acid.

Heart rate monitors and watt meters provide hard, objective data - how hard the cardiovascular system is working and the watts of energy being developed by the leg muscles. Both reflect how hard we are pushing ourselves during training and in competition to be used as a yardstick to allow a consistent scientific approach for training and competition.

These new biosensors provide additional physiologic data on a real time basis which might help us fine tune an ideallevel of training stress and assure that during competition we have enough fuel (real time glucose monitoring) and are riding at the sweet spot on endurance rides (lactate monitoring).

As I don't compete, a lactate sensor level of fine tuning is more than I need, and just as with the HRM and watt meters, perceived exertion is an ideal integrator of physiologic inputs for both my training and long rides at level 2. But for those looking to get a final tweak in their performance, these two biosensors will provide the necessary data.

If I had to pick one of the 4 monitoring options, it would be lactate monitoring. It is associated acidic end products of muscle metabolism (not necessarily lactic acid itself) that limit maximal performance. In training, we want to push our %VO2 max to a level that lactate removal systems improve but not so far that excess lactate limits the duration of our training (anaerobic intervals). And for endurance events, we want to push ourselves, but only to a degree that avoids a slowly rising blood lactate level which will in turn limit muscle performance.

Now a bit more on the pros and cons of hard data (HR and Watts) versus perceived exertion.


Do all those gadgets (HR monitor, power meter) and laboratory tests (lactate levels) give you a training edge compared to the use of perceived exertion? It's not clear - and when you look at their costs and the distraction of using them, as well as the potential to injure yourself if you are mindlessly training to the numbers, they may actually keep you from maximum improvement. We know that improvement requires stressing the muscles to the point that structural injury occurs. Repair of the injury leads to adaptation and better performance - the logic (and science) behind interval training. But the HR does not always reflect the stress level we need. If you are feeling tired, a HR determined on a day you were rested might now lead to overdoing it with an increased risk of injury.

We have all have had that day when our heart rate and level of performance seem to be out of sync - a "bad day". On those days we should listen to our body, not to our gadget. Chasing a number risks injury. Likewise on a good day, we may reach our HR goal yet feel we still have more we could do. On these days we should again use perceived exertion rather than a HR number for that day's interval goal.

A comment from my page on pacing is just as relevant to the debate on using a HR monitor/power meter versus PE. The influence of clock watching (sic - you can insert HR or watts here) on training is two-sided. The same number goal that enhances performance when it is perceived as a target constrains performance when it is perceived as a limit. The potential for numbers (heart rate, watts) to become training limiters is most apparent at the elite level of endurance sports. And this was why Armstrong did so much better without the numbers - and just pushed himself to the limits he felt.

Perceived exertion could be looked at as our conscious awareness of our central governor, the integration of multiple physiologic inputs which then help to protect us from injury by setting an upper limit on our level of exertion. That tight rope of enough exertion to provide maximal stress without overdoing it and increasing the odds of injury. And our central governor is the most sensitive measure available to integrate all the internal measures that your body's is using to monitor (your dash board) how the "engine" is functioning. It is multiple inputs include such things as "..lactate levels, VO2max, heart rate, heart-rate variability, rapid morning heart rate, recovery heart rate, hormone levels (cortisol, testosterone, etc.), red cell counts (hemoglobin, hematocrit, red cell indices), immunity (white blood cells, interleukin, inflammation), muscle damage (creatine kinase, oxidative stress), blood pressure, and much more."

As Dr. Mirkin put it: "....the devices cannot tell you whether you are exercising intensely enough to gain your maximum improvement in ability to take in and use oxygen or to damage your muscles enough for maximum strength gain. Only your brain can tell you whether you are at your maximum, if you need to take off because you are about to injure yourself, or when you need to slow down because you are exhausted. Fitness gadgets can help to motivate you and can be fun to use, but do not count on them to tell you how intensely you should exercise or when you are at the edge of an injury."

I could not find the original article he referenced but I'll quote: " from Deakin University in Australia reviewed 56 studies that compared the way that electronic devices and your brain tell you when to slow down or stop exercising (Br J Sports Med, September 29, 2015). Half of these studies showed that the brain and sophisticated machines were equally effective in telling you that you are training too intensely and need to reduce your training. The other half of the studies showed that 85 percent of the time, the brain was a better gauge of over-training than sophisticated machines."

My bottom line? Although monitors are a great tool, and do help keep us engaged with our training program, if I had to choose, my preferred approach would be based on a program of structured stress (intervals) using perceived exertion as my measure of maximal stress rather than a single number such as heart rate or power output.


There are several ways to categorize your level of PE. This scale ranges from 6 to 20, with a literal description for each level of exercise intensity.


It was designed so adding a 0 to the level of exertion would give a rough estimate of your heart rate i.e. if you were resting (a 6 on the scale) your heart rate would be in the neighborhood of 60. Although RPE isn't accurate enough for detailed physiologic studies, research has demonstrated an amazingly high correlation for any individual from day to day. In other words if you felt you were exercising at a 13 (somewhat hard) on two different days, and checked your heart rate, it would be quite similar.

A somewhat simpler 10 point scale can be found in this online article.

How can you most effectively use RPE? First familiarize yourself with the descriptions of the levels. Then, using a treadmill or wind trainer, rate your own level of exertion BEFORE you check your pulse rate. With a little practice you will find that you will be amazingly accurate in predicting your heart rate. At that point you can use your own RPE instead of a heart rate monitor to monitor the intensity of the day's workout.

Additional thoughts

RPE can change as fitness improves and with factors such as hydration, carbohydrate status, and ambient temperature. So recalibrate your own RPE scale regularly during the season if you are using this tool in your training. A heart rate monitor or a watts meter are important tools. But when it matters most, your carefully honed self-perceived exertion level is still the best monitor ever created.

It has been shown that caffeine decreases perceived effort and muscle discomfort with aerobic activity (cycling). Interestingly, this effect was not the case with the use of aspirin as comparison.


If you didn't have access to a sophisticated exercise physiology lab, the first readily available training "gadget" for a cyclist was the Polar heart rate monitor brought to market about 50 years ago. Another ten years and power meters were added as another option. Today in 2024 we see oxygen saturation numbers being added to the data mix and complex artificial intelligence algorithms then applied to determine the "ideal" training program.

Interestingly you can have access to a simpler and less expensive (free) natural integrator of your physiologic data by using Perceived Exertion. Cyclists tend to be techies. They like gear, gadgets, and graphs of performance. But Rating of Perceived Exertion (or RPE) is, I think, just as useful and under-rated as a training metric.

This article does a great job reviewing all aspects of RPE. And provides solid support for reconsidering this simple, inexpensive, and holistic assessment of how hard you're working as a guide for an aerobic training program.


Question: I want to improve my power at lactate threshold (LT) so I can excel in time trials and on long climbs. But I don't know how hard to ride during LT training. Lab tests are expensive, I'm told that heart rate is unreliable and I don't have a watts meter. Is there a simple method for nailing LT intensity without all the black magic?

Answer: PE can be used in 2 ways. First is with intervals. Here you want to be a 10 for 30 to 40 seconds. That will maximize your effort and provide the interval training benefits.

The other is to use PE to ride at your lactate threshold for longer periods.The following comment is quoted from as it nicely summarizes the concept.

LT can be gauged by wattage, lactate accumulation, heart rate or perceived exertion. The first requires a relatively expensive power meter as well as a lab test to find your wattage at LT. Actually measuring lactate means periodic blood draws -- not too practical while you're riding the road. And heart rate can vary for a given power output due to hydration status, environmental conditions and other factors.

That leaves your personal rating of perceived exertion (RPE). In other words, how hard you feel like you're riding. In the old days, everyone trained with RPE. Before heart monitors there was no other way. The good news is that research shows RPE is an effective way to determine intensity.

Allen Lim did ground-breaking research on cycling power while working on his Ph.D. in exercise physiology at the University of Colorado. In an e-mail he wrote:"Training prescriptions don't need to be overly complicated. If athletes are in tune with themselves and quite experienced at perceiving effort, then what they perceive as hard can be used consistently as a reference point for training-induced adaptations and for determining training pace."

So, if your workout calls for a 20-minute effort at close to your LT, it's fine to forget the technology and simply ride at an intensity that feels hard. You'll be close to your lab determined ideal intensity.

How hard is hard? Think of effort on a scale of 1 (lying on the couch) to 10 (riding flat-out and suffering). On this simplified RPE scale, LT intensity is between 8 and 9. This is the point at which breathing is at the breakpoint between hard but steady and labored with gasping. Another way to find it: Increase intensity until you begin to gasp, then back off a notch.

All questions and suggestions are appreciated and will be answered.

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