Eric's Arcana and RiderX

I had an idea a while back.

I’ve noted in my previous article about cadence that riding a slower cadence can be faster. And I’ve been playing around with this on rides, and found that a cadence of about 80 seemed to require less effort at a given heartrate – I can ride at 150 BPM and 80 RPM much easier than 150 BPM and 95 RPM.

But is it a real effect, or am I just imagining it? Well, it’s fairly well documented that fast-twitch fibers are less efficient because they (at least some of them) use anaerobic metabolism, but I’m not sure where the switchover is or if that’s what’s going on.

Time to do a ‘spearment to find out…

The hypotheses

1. At a given heartrate, power output will vary inversely with cadence (ie I will generate more power at a lower cadence than a higher one)
2. At a given heartrate, perceived effort will vary directly with cadence (ie I will feel better at a lower cadence than a higher one)

Experimental method

Ideally, one would use a power meter, but this one doesn’t own a power meter, so I’m going to do it by measuring speed on a hill climb. It won’t give me absolute measurements, but it will give pretty good relative measurements.

The plan is to do repeated hill climbs at various cadences – I’m going to start at 100RPM and go down from there. I’ll to try to to stick around 140BPM, since that heartrate is just a bit below my LT heartrate.

The test

I picked a dry Sunday morning to do the test. I go out and warm up thoroughly, including one climb where I spike my HR up above 160 (if you don’t do this, your results will be less repeatable). I set my Polar (720i) so that it shows cadence and total time (I don’t want to see speed since it might influence me).

I head over to my test hill (NE 8th up from Northup in Bellevue), shift to my lowest gear, and start spinning up at 100RPM. 30 seconds later, I’ve stabilized on the climb – at 70 RPM and 160 BPM. It’s waaaay too steep for this test, but now I’m very warmed up, so I head over to 164th.

I descend to the bottom, stabilizing my HR at 100 BPM, then I turn around and crack up to 100+ RPM and shift and get my HR to 140BPM, and head up the hill. 0.9 miles later I turn off at the top and coast (so I can find the top in my data log), descend and repeat at 90 RPM. Then 80 RPM. Then 70 RPM, and home to read in the data and do some number crunching.

The data

I import the data onto my laptop, and select each section of data. Here’s a table of the data:

The first 4 items are directly from my polar softrware. I used the Bicycle Power Calculator to estimate the wattage.

I’m pretty impressed by the how close I got to my target on both the HR and the cadence.

Here’s a pretty graph:

Perceived exertion

It takes a fair bit of attention to watch your cadence and HR and shift up and down to keep them in the right range as the gradient changes, so I only have my recollections.

The first trial was pretty hard, I was fairly out of breath. The second and third ones got easier. The last one was really hard on the legs and I was a bit toasted at the end.

Discussion

The data quality is better than I expected – you could fit a very nice curve through the points. Going from 103 RPM to 80 RPM increase my wattage 20%, which is a lot more than I expected. Going down to 70 RPM nets me another 7% or so, but I don’t have the leg strength to do it for long. It’s weird that I see an improvement because if I fatigue quickly, I should be falling back more on fast-twitch fibers which should make me less efficient, not more.

On the other hand, I have been working at improving my leg strength which means I’ve been riding a lot at 80 RPM (or lower) on hills in my aerobic zone, so there may be some training effect there.

That’s assuming that HR is a reasonable proxy for energy use, which I believe is true.

So, what does this mean for other people? Not really sure. So go out, give it a try yourself, and let me know what works for you.