mah powerband

Base: A New Definition

Mitochondria: Aerobic Engines

Stripped Down

Project: Rolling Resistance

Stems

Power Meters

Wheels

Mah PowerBand Don't Kick in 'till 90 RPM

Words and images by: Kraig Willett

I've had my ass handed to me in many a city limit sprint by some of the biggest slugs you could imagine. I'm so slow that you'd probably lap me in a 200m sprint!

Well, thanks to my power meter, I now have hard data that shows why I was never known for my wicked-fast jump. My PowerBand (TM) don't kick in 'till 90 RPM...

In many years of racing, I won exactly one field sprint. If my memory serves me right, it was at the Silverton, OR road race in 1993. It was kind of a long run-in to the finish and the speed was high all the way to the line. I judged my final surge just right, got real lucky, and pipped Dave Douglas at the line in a photo finish - for 10th place...

I've been in small breakaways dueling it out for high placings and the occasional win, and I have been the most successful when I go for the line from a long way out - I learned that I won't win a short, slow starting speed sprint. It took me quite a few losses to figure this out (probably a lot longer than most, since I am so stubborn with some things).

The scenario was always the same in these types of sprint situations - a huge gap would open from the get go, and then I _might_ hold my own to the line. I didn't have a jump then, and I still don't, but I did some interesting data collection over the past week that might shed some light on the characteristics of my motor, and how using the right gears might help me out a bit in the next short sprint I am forced into.

Experimental Method

Since I was focusing on the initial jump phase of a sprint, I rather arbitrarily decided that this was defined as the first four full pedal revolutions. Could one define it differently? Sure, but four rev's are what I brung, so to speak...

I set my new-to-me SRM Pro to record data at 1-second intervals and did three jumps at various discrete starting cadences (10 30 50 70 90 100 110 120-> these should all have an 'ish attached to them). The reasoning for the three jumps was to provide an average value that reduced any weirdness with the SRM at low cadence values. All jumps were done in the same gear, a 53x18. I allowed myself to recover in between each four pedal revolution effort and tried to start each effort at the same level of "rested-ness" - perhaps to some people's dismay, I used HR to measure this level of recovery. In order to achieve the 140's HR level I used as "recovered" during the high RPM trials, I had to do these on downhill sections of roadway.

Results

Despite my attempts to help out the SRM at low cadences, I had an unexpected result in the pedal load vs cadence plot - instead of large pedal loads at low cadences, the SRM reported relatively low loads; it was an unexpected trend. Therefore, I have discarded these data and wound up with the following plot of pedal load (blue) and power (red) vs cadence below:

The pedal load vs rpm trend is as expected in that it is fairly linearly decreasing. What is very interesting, at least to me, is the shape of the power curve. At the high RPM's, power output remains fairly constant - this high power range is what many drag racers call the PowerBand, or the RPM range where effective power is generated. In the lower RPM range, there appears to be a linearly increasing power trend from 50 RPM up to about 90 RPM (OK, I just eyeballed that, but it looks pretty linear).

So what's this mean? Well, it means that my PowerBand doesn't kick in until 90 RPM!

I wonder what this kind of plot would look like with a sprinter who had a good jump... Would the slope at the lower RPM's be steeper, and the PowerBand span a larger RPM range? It doesn't seem like much of a stretch to think that could be the case, but this is pure speculation on my part.

I think this plot also shows the importance of being in the right gear at the beginning of a sprint. If I could start all my sprints at 90 RPM or greater, I have a better chance at not getting holeshotted. Being in too big of a gear cuts into my initial peak power production by 30-40%, and it's tough to get that kind of a deficit back over 200m! I think that in really slow-speed starting sprints, I won't have a gear small enough to start at

90 RPM, so I had better plan on not letting that situation ever happen!

Of course, when you are as slow as I am, even all this data-obsessing still might not help - kind of interesting, though...