Originally Posted by
mschwett
so, 6 weeks later, i have a couple conclusions.
my power is completely limited by cardiac output (probably the case for everyone?) and my unwillingness to roll the dice and see what happens above a heart rate of 130. it's also incredibly difficult for me to get there somtimes, with extreme short of breath setting in around that same rate, likely due to inadequate heart function anyway. in any case, not worth the risk, at all. i can enjoy fairly hard and fast rides in the 90-120 range with a few little spikes to 130 for short durations.
watching HR and power a little more closely since i made this post, the mystery is really why on some days/times my HR is about 10 bpm slower for a similar "intended" effort, which results in about 5-10% less power. i can try harder, but perceived exertion and shortness of breath is way higher, and it's not satisfying. i'm not racing anyone but myself, so i've started to throttle back on those rides, just taking it easier when it seems my heart just doesn't want to do the work. the primary factors seem to be time of day (earlier is worse) and weather (warmer is much, much, much worse.) i don't think there's been any or much change over time that isn't explained by those factors, for the most part.
the power-hr correlation is clear. the trend over time is not really a trend except that the weather follows a trend, and my riding patterns aren't totally regular. some weeks there are more morning rides, some less, sometimes there are more urban rides which have more start and stop, sometimes more rides on a familiar course that i can hammer (if i feel like it) for an hour without stopping. here's an update of the power-hr scatter and the "best hour power" for 6 months, solid data with a few outliers where my hr strap was clearly off removed. in all cases, the same bike, same power meter, dual sided, zero offset at the start of the ride.
Perceived effort and actual power output variation are common with people that have perfectly functioning hearts too. Day to day variation can be dependent on rest, fatigue, training status, sleep, diet, etc. I wouldn't sweat that, it happens to all of us. And yes, cardiac output is a limiter for most of us. If your vo2 is 95, it probably isn't a limiter, but if it's 40, then I'd say chances are very likely. If you have heart issues, and you limit your heart rate to 130, then of course low oxygen capacity is going to be a limiter of higher end power. I'd be curious as to what the docs say about doing LONG efforts. Like zone 2 for 3+ hours. Endurance and fitness can still be gained by doing those types of rides. I'd also be curious if your heart condition is able to improve with endurance rides as well.