GaryWSmith said:.. then would heart rate not be affected one way or the other and therefore be of some use when used in combination with power data. The assumption is that heart rate will be higher for the higher cadence sessions and I guess it could be a faulty assumption.
I agree that HR is typically higher at higher cadences, but is that a problem or something you should use to taylor training? When I've used HR to limit or guide my efforts I've tended to undertrain in fear of the high HRs.
Looking back at power/hr curves I can see that HR tends to climb steadily throughout a constant power interval. It takes about a third of a 20 minute L4 effort for my HR to reach the mean for the effort and it continues to climb all the way to the end. This is true for both indoor and outdoor rides regardless of cadence. The HR may actually be higher if I stay in lower gears and spin faster, but how will that information help me? I suppose I could stay in higher gears to avoid the higher HRs, but I really do believe that developing the ability to generate power at higher RPMs is real useful for racing.
It seems that using HR to guide intervals leads to artificially limiting your efforts in fear of high numbers. Either you drop the power to keep the HR in some predefined range or you limit your cadence and drive bigger gears to get lower HRs. Either way it seems to place unecessary caps on your workouts. I guess the unstated premise is that high HRs are somehow a problem and should be avoided. I don't believe that, I certainly used to but no longer do.
Physiologically there's definitely a difference like a tradeoff between higher force per pedal stroke and the need to fire your muscles more frequently at lower forces. It's those differences that convince me it's worth training to expand your useable range of cadences at the powers you need to produce to be competitive. I wonder if high cadences are specifically a problem since we tend not to train them as much. I have noticed when I ride ergs at constant power I tend to spin faster near the end of my long (20 -30 minute) intervals. I often find myself spinning 95 - 100 rpm near the end of a 2x20 L4 repeat when riding fixed power ergs. I haven't paid attention to HR at those times but I'd guess I'm happier putting out less pedal force at a higher rate as I tire. Maybe that comes from years of fixed gear and track riding or maybe it says something about my force/speed curve but I often spin fast in these situations. It doesn't seem to directly translate to the road where gear shifts are incremental and spinning a given gear faster requires more power.
I see your point that HR might be related to physiological stress and therefore might be a second order gauge of some sort. I just can't see a way to make that data useful during a ride. Perhaps afterwards it could be a way to gauge whether the same workout on different days was more or less stressful and might be a way to keep tabs on overtraining and the need to rest or push. I'm just thinking out of the box here, but I don't see how HR is useful while you're actually in the field during your workouts. I guess I just spent too many years really believing in HR as a good gauge and all my power/hr data has shown me I was chasing ghosts and limiting my efforts for the wrong reasons.
-Dave