Effect of cadence and position on HR and RPE

I use TR for general purpose aerobic fitness, but also specifically for track pursuit training. My set-up mimics my pursuit bike, with aero bars etc. I know that lower cadence is associated with lower RPE and some efficiency gain, but with a fixed-gear bike on the track, and the effort taken to get going from a standing start, my target is around 106-108 rpm. So I do intervals in the aero position at 106-108, following TR’s advice regarding specificity and all that. Yesterday was a bit of a boring recovery effort (Townsend I think), so I started playing around. At 210 watts (erg) in pursuit mode (aero position and 106 rpm), my HR was about 112 bpm and I’d give it an RPE of say 5. Then in the same interval (they are very long intervals) I tried sitting up, putting my hands on the arm pads and arms straight, and dropping the cadence to 80 rpm. My HR goes down to 98bpm, and my RPE is about 3. I repeated it, with very similar results, and no fatigue or anything is creeping in, I’m well rested. So then I thought what watts would 112bpm in the sitting up position be? I added 10% watts, nope, still too easy, 15%, nope, still not even at 110bpm, but +20% (252W), yes, I’m at 112 bpm and an RPE about 5-6. So sitting up and grinding a cadence of 80 appears to be 20% more efficient than aero at 106rpm (stationary, obviously). Is this likely true?

You measured it, so the observation can’t be wrong. Whether it is more efficient is a different question. I think maybe while you’re fresh - you can use more of your muscle mass at a lower cadence, and as long as they aren’t hard efforts, this will feel easier. Once you have fatigued the fast-twitch fibres with some sprints, this might not work anymore.

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You make a lot of assumptions, and present them as facts… Yes: lower cadence will usually result in lower heart rate, because you (slightly) shift the effort from cardiovascular to muscular. However that doesn’t mean that the RPE will be lower. The RPE would depend on your preferred cadence for that effort, and the fitness and the relative tiredness of muscles, heart, etc. That’s all very personal, and may also change with training. E.g. training with different cadences may shift your bodies preferred cadence for a certain power.

So sitting up and grinding a cadence of 80 appears to be 20% more efficient than aero at 106rpm (stationary, obviously)

It looks like you’re basing this on power vs heart rate. So more efficiency per heart beat? I’m not sure what conclusion you’re looking for, but it doesn’t extrapolate to other more intuitive cycling metrics for efficiency, for instance how far or long you can go on that power.

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I would try doing the same experiment but at ~threshold power. Optimal cadence typically rises as power rises. E.g. at Z2 I’m often cruising very comfortably at 80rpm or lower, pushing sweetspot I’ll typically find I’m at more like 90, threshold would be mid to high 90s, VO2 and higher I’m usually spinning over 100. If I try and spin at >100 on those Z2 efforts then it certainly feels harder and HR rises.

Would also try doing the same experiment but separately for different cadences, and then for different positions so you can try and figure out how much each is contributing to the HR and RPE changes.

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