Wednesday, May 16, 2007

Pedal force & muscle fatigue

Past testing has shown me that I achieve my highest power for a constant heart rate (150 bpm) at 65 rpm. My power is significantly higher at that cadence than at 55 rpm or 75 rpm. That's a lot lower (about 20 rpm lower) than my normal cadence. I've more or less ignored the heart rate/cadence data due to two assumptions that I've held:

1. The goal is not to achieve the lowest heart rate, it's to put out the maximum wattage.
2. The higher muscle force required to hold the lower cadence at a given wattage would result in power fade on longer rides more than would a higher cadence with lower muscle force.

This past week's experiments with higher pedal force (a low-cadence hill repeat session last week and last night's group ride) revealed an interesting new wrinkle: My perceived exertion is significantly less when climbing at high power and low cadence than it has been with higher cadence. I guess that's to be expected because the higher cadence climbing is putting a larger share of the physiological load on oxygen transfer (aerobic system). The higher force, lower cadence approach is much more anaerobic. My average pedal force for the 1-minute interstate hill climb on Pate was about 600 lb-in (that's equivalent to alternating 90-lb one-leg squats). That's a lot higher than my typical pedal force of around 450 lb-in.

So the question boils down to this: Can I reduce my cadence when climbing hard and still have the same amount of gas left at the end of a 2 to 4 hour ride. If so, I think I can climb faster with less pain -- and those are both good things.