More on Power Meters

The diagram here (click to enlarge)  illustrates what happens to heart rate, rating of perceived exertion (RPE), speed, and power while riding a bike steadily uphill, coasting downhill, and then on flat terrain. (Please pardon my crude drawing—an artist I’m not.)

Notice that as the hill is steadily climbed heart rate and RPE rise while speed and power remain fairly constant. Coasting down the hill, speed increases as heart rate, RPE, and power decline.

Note that heart rate was slow to respond as the rider started up the hill and continued to increase in the early part of the descent. This lag is common with heart rate.

RPE increased on the climb also as fatigue gradually set in. It rather quickly decreased on the downhill side before rising again as pedaling was resumed on flat terrain.

Speed remained constantly low on the uphill, increased on the descent, and eventually settled in at a steady rate with the return to flat terrain.

Following a steady level on the climb, power quickly responds to the transition from climbing to coasting and from coasting to pedaling on the flat section. It reflects some of the changes taking place in the other three, but does so rather quickly.

The higher the power up the hill and on the flat terrain, the greater the rider’s performance. The same can be said of speed. Only power and speed are directly related to performance. Heart rate and RPE tell us nothing about performance—they simply reflect what the rider is experiencing. But when compared with power, heart rate and RPE also tell us something about the rider’s fitness. When power is high and heart rate and RPE relatively low compared with previous rides on that same hill, we know that the athlete is fitter and faster.

Both the performance and the experience of creating the performance are important. These may be referred to as “output” (power and speed) and “input” (heart rate and RPE). The most reliable for training and racing purposes are power and heart rate (the exception being in bicycle road racing when RPE is critical to dealing with all of the sudden changes in intensity). Comparing these two makes measuring progress in training much more meaningful. If you know only your heart rate you are lacking the most critical piece of information—what you are accomplishing with your input. Training with a power meter is like watching a movie in 3D instead of only in 2 dimensions—much greater depth and meaning.

Comments

[Mike Rehab]

If your RPE isn't zero when coasting down a hill surely your perception needs calibrating.

[Joe Friel]

Mike--The typical RPE scales are 1-10 and 6-20.

[Bruce]

Hi Joe, I think you're a great artist! I especially like your renditions of the bicycle :) Kidding aside, I really like the picture; it's a perfect example of a picture worth a thousand words.

One question: about how long would it take heart rate to stabilize while riding up the hill? If it varies depending on an athlete's fitness, what's a typical range? Thanks.

[Mike Rehab]

Hi Joe,
Thanks for the reply.
The RPE on the graph is higher coasting down the hill than it is when riding on the flat.
I'd suggest the RPE while coasting should be 1, or 6. depending on the scale used.

Your graph suggests the subject is very poor at determining their own RPE. Of course a power meter is better than poorly determined RPE.

Personally, I base my RPE on how hard I feel I am turning the cranks, rather than the feeling in my heart/lungs/legs.

I feel I increase the accuracy of my own RPE by determining my RPE before looking at the Watts/HR output of the WattBike I use 2X a week.
ta.

[Chris Sharrock]

This is so bizarre. I was actually thinking about your last post regarding the delayed heart rate response to power output on my training ride just a few minutes ago. It would be great to have a power meter but sadly I can't afford it while at university. One day!

Thanks for your posts, keep them coming; they're very thought provoking!

[Joe Friel]

Hi Mike--I see your point now. I consider RPE to be a reflection of what the body is experiencing. So at the top of the hill when just starting down and HR and breathing rate is still along with perhaps muscle acidosis in legs RPE would still be greater than 1/6. At least to my way of thinking. Thanks for the comment.

[Joe Friel]

Hi Bruce--Good question. It would depend on how long the hill is and how intense the climb is (assuming steady all the way up). It could take 3-5 minutes if riding at near lactate/anaerobic/functional threshold. The more fit the athlete is the longer the delay.

[Madeleine]

Is there anything to be learned about the athlete's rate of recovery from the downhill coasting part of the heart rate curve?

[Joe Friel]

Madeleine - Probably not a lot as it is unlikely to be precisely repeatable experience. But the faster HR falls during recovery the more fit one typically is.

[Mark]

Hi Joe,

I have a question regarding training with power on a turbo. I have the choice of setting a power level that the turbo will maintain or I can set a slope and then choose my gearin/cadence to achieve my target power.

I find that with the power level set, my cadence will drop near the end of the last/last couple intervals but I maintain the power level. With the slope approach, it is harder to maintain the power output even with adjusting my cadence either up or down with gear changes.

Is there a benefit to one approach over the other?

Cheers,
Mark

[Joe Friel]

Hi Mark--Every set of workouts has both up and downsides. You need to whatever comes the closest to having you prepared to do similar workouts on the road when the weather allows.

[Barry Eyre]

Hello Joe,

I have been following your training bible book for several months now and am about to enter the build phase. All my training has been endurance and tempo with no focus on anerobic intervals. I have done a weight lifting program which is a first for me.. This week I did a 1 minute max wattage test. In your opinion, where should I be relative to my max 1 minute output last year? below? above?

Thanks your your input.

Barry

[Levi]

I'm loving the diagram, but my initial reaction is similar to the point from Mike Rehab. It appears the RPE is more like a "Rating of Perceived Discomfort."

I've always considering my RPE number to come from the power meter lobe of my brain if that makes sense. Basically, if you're used to thinking in terms of power, you'd be better at gauging RPE. In contrast, if one analyzes everything based on HR, their RPE is likely to reflect their HR (much like the diagram.)

[Joe Friel]

Levi--Good comment. Understood. Thanks!

[Joe Friel]

Barry E--At this time in the season (I'm assuming a lot here like which hemisphere you are from) most athlete's power numbers lag behind last year's. But the shorter they are (as in 1 min) the more likely they are to be similar (again, an assumption here that you are an endurance athlete).

[Barry Eyre]

Hi Joe,

Thanks for your response to my question.

I live on the east coast of the usa. I am road racing cyclist doing races up to 65miles, so I guess that makes me an endurace athlete. My 1m number was 95% of my max from last year. last year it took me until June to reach the 1 min power output I hit last week. I am curious that you say the 1m power is likely to be similar. I thought that we humans lose the top end fitness first. Is that not why we can't peak for very long? because the anerobic fitness (which is what I need for a 1m interval) is very hard to maintain.

puzzled in Rhode Island.

[Joe Friel]

Barry Eyre--Anaerobic alactic fitness doesn't change that much, esp given that endurance athletes are not all that well designed for this level of stress.