Originally Posted by
Ric Stern
It's worth understanding that a higher rather than a lower cadence is less efficient at a given power output, and that training at low cadence (for steep hills) is *ineffective* for building strength. This is because even though it may feel like you are strength limited at low cadence, you're not (presuming you're able bodied). For eg at 400 W at 50 revs/min on 172.5 mm cranks your average effective force is 443 N between both legs, which is about 45 kg (about 100 lb). It's highly likely that your weight is much more than this and you can e.g. stand on one leg, or walk upstairs unaided. Presuming your pedalling is roughly equally shared between each leg, then the average effective force is 22.5 kg for each leg, with a peak force about 1.9 times higher than the average force (i.e., about 43 kg per leg). of course, if you're unable to sustain 400 W and you ride at a lower power then the average effective force would be reduced (eg at 300 W it's about 330 N, at 200 W about 220 N all at 50 revs/min). Conversely, if you can ride at 60 revs/min instead of 50, then your AEPF at 400 W would decrease to ~ 370 N, etc.
If you want to increase your leg strength (and you should want to - both for health and performance) then strength exercises in the gym are the way forward.
Unless there's something wrong with your heart, then your HR doesn't limit your legs. It may seem that way, but HR is a dependent variable, while power is the independent variable. HR is only part of the equation - there are changes that occur in cardiac output due to changes in stroke volume. Of course, as your exercise intensity increases, and your HR increases there's a multitude of physiological issues going on which cause fatigue in many ways. These are significantly harder to measure than either HR or power and for most of us the only physiological metric we can see is HR and so we often feel that it's that causing the fatigue/slowing down/drop off in performance etc
Very interesting thanks. I see HR as the red flag when I'm pushing hard, whether on a hill or flat. Once I go over FTP my HR starts to creep up until it eventually maxes out (which happens quicker the further above FTP I ride) and then I'm forced to back off and recover a little. Once my HR starts to come down I can start to push on again, but usually at a reduced power level. If I'm fatigued toward the end of a long ride, my HR stays lower but I find myself power limited.
For example yesterday I did a Zwift ride ending with a full gas climb up Leith Hill. I went hard up the first steep pitch at around 400W and my HR climbed from 165-192 (my max) over 0.5 km. At that point I backed off a little to around 350W (I wasn't watching my HR, it was just instinctive) and my HR came back down to 175. Then I pushed again at 400W and my HR went back up, but this time peaked at 185 before I felt the need to back off again. My HR then went back down to 175. Then on the last steep section I went again, but this time I was struggling to hold 300W while my HR again hit 192 and then I had to back right off for a few seconds before one last push over the crest at 400W which left me gasping for breath on the limiter.
I realise it is the power level driving my increase in HR, but it's my HR that I feel sets my power limit (in terms of duration at a given power) in these situations. At least while I am not overly fatigued. When I am very fatigued my HR response becomes much less dynamic and my available power range shrinks!