Hi,

I recently started working out with a HR monitor, and decided to do a little experiment on my trainer. The results surprised me, and were different than I was expecting. I'd like to get some feedback.

Background:
I've been a strong recreational biker for the last couple of years. Early on I read about the importance of maintaining relatively high cadence, and took that to heart. Working out on the trainer, I'm comfortable spinning 90-100rpm, start "working" between 100 and 110, and am pushing it a bit to hold 120. The max cad I've hit on the trainer is 188, no bouncing. On the road I routinely ride 60+ miles at 18-19mph, maintaining an average cadence in the high 80s.

Based on all this, I felt that somewhere around 85 would be my most efficient cadence.

I'm 41, and have always had a fairly high HR, here are my base numbers:
Resting Heartrate 58
Max Heartrate 193
Working Heartrate 135


The Experiment:
I wanted to find out what cadence (gear ratio), would give me the lowest heart rate for a given power output. Like I said, I expected this to be somewhere around 85rpm.
I have a fixed load fluid trainer. I chose a speed which gave me a "moderate" effort, of about 80% perceived effort - 14.1 MPH. According to my trainers (difficult to decipher) documentation, this should be somewhere around 150-200 watts. I warmed up for 1/2 hour, then started the test. This consisted of soft-pedaling in a low gear (38/26) until my heart rate hit 155, shifting into the "target" gear, then adjusting my cadence to hold 14.1mph. I held that cadence for three minutes to let my HR adjust to the load, then took an average HR for the next two minutes. Then back to cool-down to 155 before the next test.

Here are the results:

Test Spd Cad Gear HR % MHR
1 14.1 107 38/23 175 86.4
2 14.1 96 48/26 168 81.2
3 14.1 85 48/23 167 80.4
4 14.1 74 48/20 163 77.4
5 14.1 63 48/17 157 72.9

Much to my surprise, as you can see, there is a direct relationship between my HR and cadence at this power level - the lower the cad, the lower my HR. I can definitely say the lower cadences were less "comfortable", with noticeable lactic acid build when turning 74 and even more at 63.

This countered my view of cadence efficiency.
What are your thoughts on this? Should I be training for long rides (centuries) at a lower cadence?

P.S. I have yet to repeat the test at a lower (or higher) load...that may change the results.