In case anyone out there benefits from reading this: search keywords: knee pain asthma COPD exercise induced bronchoconstriction wind chill turbo trainer different from road heart rate
I've done some more workouts on the trainer and some research. This is most likely my final word on it unless anyone else wants to start a discussion. Bit of an essay but if you're not interested, feel free to go on to the next post
Executive summary: I, like most people with asthma, have lungs that are less efficient in cold air, so I can't work my legs as hard outside as I can on the trainer, hence I overdid it when first using the trainer.
PeterH
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Details:
First, now that I have the smaller (28mm tyre) installed and I am not overtightening the clamp, the resistance is noticeably less on the turbo trainer. Also, now that I have been using it twice a week for several weeks, I can feel that I am able to pedal harder without knee problems, and I think I can detect some muscle development in my thighs. I'm also working on pedalling style and doing some short (!) intervals at slower cadence in a higher setting on the trainer. I suspect that my normal "twiddling" style of pedalling fast (100rpm+ typically) in low gear which I adopted after my original knee problems has meant that some cycling specific muscles in my legs are (were) not so strong (most leg strength work is normally done in the gym and on a rowing machine).
But back to the heart rate conundrum: this is (I think) the real story, not the knee.
I have mild asthma and hay fever, normally well controlled with standard medication. I did some research on the internet and found some articles and peer reviewed papers in sports medicine journals which report that most people with asthma or COPD will experience some level of exercise induced bronchoconstriction or "EIB" (a form of exercise induced asthma) if they exercise hard, and that this effect is very common when doing endurance sports in the cold (e.g cycling, cross country skiing, running). Cycling at speed other than on a warm summer day brings wind chill (in April though it feels warm in the sun, the actual temperature experience when moving into the wind is still quite chilly- I am wearing a mid-weight jersey over a base top when out).
I believe that this is what is happening. When out on the bike, my lungs are the limiting factor in my effort. I am breathing hard but because of the EIB (which I can feel as a slight tightness) my heart works harder to get the most out of the air delivered (this effect is also well documented for when you are at altitude, and again, I experience it when I go to a ski resort for the first couple of days). On the trainer, I am not moving, and so don't have the wind chill, and hence little to no EIB.
Over the weekend I did a couple of 1 hour road rides, being quite active, though not really pushing my legs to their limits. HR was typically 130+ other than downhill
and frequently spiked up to 140+ with maximum around 150. My lungs felt like they were working hard, and I took care to ease off when the HR got towards 150, though my heart felt fine. This is pretty normal for me. At one point I stopped and took my pulse as I thought maybe the HRM was malfunctioning, but no, it really was over 140 at that point. (In case anyone reading this is concerned: I did have my reliever inhaler with me and I never felt unwell - no hint of an asthma attack - was being careful to watch the HR reading on my cycle computer - and was not tired when I got home.)Today I did a 30 minute static workout plus a few minutes warm-up and cool-down, in our garden room with the garden doors open. It included intervals which worked my legs as hard as they ever would cycling on the road. Maximum HR was 130 near the end before spinning to cool down. I was sweating quite a lot and getting hot in light gym top and shorts by then. While my legs felt like they had a tough workout and were more tired than after the weekend rides, neither my heart nor my lungs felt like they had been worked especially hard.
So I guess outdoors my lungs are my limiting factor, and indoors my leg muscles are! I'm going to carry on using the turbo trainer as part of my regime once the lockdown is past, as it can't hurt to have stronger cycling muscles, and continue to work on my pedalling, to make it smoother and more "circular" with a slightly lower typical cadence (there are peer-reviewed papers documenting experiments which show that around 80rpm is more efficient than say 60 or 100). Wearing a windproof gilet might be an idea. I will also look into some respiratory muscle training - my breathing technique is already pretty good but there may be potential there. And I'll continue to wear a heart-rate monitor on rides.
PeterH