Wishlist : The Tools We Need

<-- prev | next -->

Here is the final word on power meters as of 08/12/08. It includes a simple bathroom scale test exercise that illustrates a major problem with all on-bicycle power meters currently available.

This comes after four months researching various systems, speaking with people who are using PowerTap and SRM, plus using the PowerTap myself in an intense training environment during that time.

I have looked at all the promotional material and the best information available online on all the systems currently available.

We are using a PowerTap (just about everyday since early February 2008), and I have spoken with people who are using the SRM, and one person who has used both.

The main defect in all available systems is the amount of delay before the amount of effort a rider applies to the pedals is shown on the display. There are other problems, but this is the big one.

I taught music in private lessons for almost 20 years, so I know intimately the difficulty of teaching rather simple concepts of eye/hand coordination even when using devices (musical instruments in that case) which give immediate real-time feedback to the student.

During those years, electronic instruments of all types became widely used. Some of what they offer is incredibly helpful for an instructor.

For example, electronic keyboards can maintain a level of correct intonation previously impossible. Even pianos that have robust tuning systems and are housed in a stable environment require periodic retuning by a specialist in the process. A sure reference to standard pitch is very helpful in training a student's ear, and training a student's ear is in reality a large part of the process of training their hands.

On the other hand, one of the largest problems with electronic keyboards is the delay introduced between the time a key is depressed and the tone is sounded. This is much less a problem with the newest keyboards, but a natural instrument can generally be described as having a better "touch" than an electronic equivalent.

This problem has always been severe when using a guitar-like interface to electronic sound sources, because in order to know which tone should be sounded, the device must wait for at least two cycles of the guitar string vibration in order to identify the pitch.

Similar to this, I have found that the major point of failure in the hopes of moving a roomful of electronic music and recording equipment onto a laptop has not been the raw power of the laptop, but the speed of response in the control surfaces and interface.

That is to say, if you adjust a virtual slider you will find the delay between your movement and the actual change is unacceptable when doing very fine work... the sort of fine work required for excellent results.

Unfortunately, the musical instruments and recording devices I have just mentioned are still many years ahead of current power meter technology in terms of valid, consistent, immediate feedback. The speed of response in all the current meters is an order of magnitude below the worst musical instruments of 20 years ago.

This situation feeds into a continuance of the misconceptions about power and speed which was supposed to be alleviated by the promise of power meter technology.

It took three months of careful work trying to get Mary to understand the simple physics behind the basic fact that a given wattage held efficiently over a more or less circular course would always result in a predictable speed. Generally speaking, uphills and downhills have absolutely no effect on this, and wind resistance is averaged out by the circular course.

One major hold up was due to the delay in the display of her PowerTap, a situation that SRM owners have confirmed to be the case with that system as well.

When we began testing Mary's maximum momentary output, she had a strong feeling that she must build effort to maximum.

She did not understand that we were trying to test her momentary strength which was actually a measurement of her first push of the pedal.

The two to three second delay after she would press her pedal before the unit displayed her wattage would only exacerbate her misunderstanding, because it continued to imply that she had to push harder, then harder, then harder before she could reach a given number.

The concept that her true maximum effort could only be held briefly, and that there is a significant drop in power within the first 12 to 15 seconds, was impossible for her to grasp.

Even after months of looking at the situation and finally understanding the reality by way of a long list of tests, checks, and reviews, our most recent work toward achieving and efficiently maintaining a goal wattage has required me to pace behind her, closely monitor her performance using a wireless CPU mounted on my own bicycle, and quickly report how the power meter is giving her misleading information.

One of the exercises I developed to help Mary understand her power output is called Pop-watts. For that exercise, I carry one of her CPU's on my bicycle while pacing behind her, so she doesn't have to watch the display but can concentrate on the feeling of the exercise.  I prompt her to "Pop" to a specific wattage.

After some success with the exercise we ramped up the requirements for success by having her hit what she believes to be the watts called for, then hold it until I confirm the number on the readout. During one series of Pop-watt exercises she was supposed to hit 200 watts with 200 to 250 within three readout changes being considered a success.

She was getting good enough at the exercise that she could hit the target generally on the second bump of the readout.

Mary would start from her warmup watts (80 to 100) and stomp on the pedals trying to hit 200. Due to the fact the PowerTap only shows averaged changes  at a little more than 2 second intervals, it takes almost three seconds for the first change of the display number. Then there will be another almost three second interval before the next number change, and so on.

Unfortunately, as she got better and better at hitting the target from the first stroke, the false results became more and significant and confusing. Often she would hit 197 on the first bump, but in cases where the second bump is maybe 198, she would not hear confirmation of how good she was doing until the third bump almost 9 seconds after the first stomp.

In that time she often panics, presses harder, then harder, so when she finally pops over 200 hundred the bump is actually to over 400. In fact, her sometimes confused hesitations between bumps can make the final display show something in the neighborhood of 130 watts for an effort which was mainly closer to 500.

If she was monitoring this on her own, she could easily miss the first or second bump altogether, and never realize just how close she had been to her goal wattage immediately on starting.

Even with my help, and discussions about the lag time in the readout, it has been pretty hard for her to gain confidence and understanding of what level of effort is required for what result in watts.

We have developed a pretty good process for dealing with this (and many more problems which are not restricted to the PowerTap but exist in the SRM as well), so her performance has benefited greatly, but there is still a lot left to be desired.

Here is a little exercise anybody with a bathroom scale can complete in order to understand exactly what I mean.

Stand on a scale near a counter in order to place your weight into your hands in order to watch how the scale numbers quickly respond to weight changes.

Take some of your weight off the scale by leaning onto the counter. See if you can hold the scale number at 80% of your actual weight.

Now shift your weight alternating from left/right foot while still maintaining the same 80% of your weight.

Close your eyes and shift weight left/right while still holding 80%.

I'm sure you must realize how hard it would be to hold a given weight number if the scale was only showing you an average of these weight changes every 3 seconds. That is the major problem with power meters. They make you wait seconds for a report when millionths of a second would be too long.

If only a power meter would provide numbers as quickly and consistently as a bathroom scale. It wouldn't even matter whether you called the numbers watts, torque, weight, power, effort, or dingleberries, just as long as the numbers were quick, reliable, repeatable, and objective.

The SRM system has been reported to display about 20 more watts for the same effort when tested side by side with the PowerTap, but even that would be totally without consequence if the numbers were reported fast... and by fast I mean immediately, right now, and in real-time.

Those who did the bathroom scale exercise on a digital scale will gain extra insight, because the method of sampling and display is the same as a power meter, so the statement, "Yeah, but the power meter has to calculate watts," will be revealed for the red herring that it is.

Displaying the number as watts is a pretty good choice, because there is a strong correlation between watts and speed, but if the same number (whatever flavor) was immediately displayed for the same effort every time, the rest you could figure out.

We need a much faster sampling rate, speed of calculation and display.

Miles per hour are rather meaningless as an index for tracking performance due to the momentary effects of wind, uphill, and downhill—unless all three are compensated by a sufficiently long unobstructed circular course.

Also, similar to your thirst, by the time your Heart Rate shows you that you are in trouble it is way too late.

Therefore, power meters are the current best reference for true effort, but it is going to be some time before they become truly useful teaching tools.

I myself will avoid (in all ways possible) spending another four months with any other human being merely trying to get them to understand: watts is watts is watts, and any efficiently applied effort in watts will result in a highly predictable related speed over time, and the absolutely best place to practice hills in on the flat.

The Widder finally understands, but it took an inordinate number or real world proofs, so as long as riders are required to wait two to three seconds for an accounting of their efforts, it is unlikely many will learn how to truly make good use of this information anyway.

<-- prev | next -->