Ahh, thank you everyone, lots to think about here.
@MN_XC and @anthonylane I probably didn’t elaborate enough about the knee pain in the initial post (not wanting to be a moaney snowflake) - I have long term knee issues which have been seen by various experts over the last 25 years, and which have been rehabbed in various ways over this time, but which culminated in a meniscus tear a couple of years ago. I have raced a 24 hr when it was still healing and it didn’t worsen it. I do, however, have to undertake long term forever maintenance physio. Squatting heavy weights helps loads, and I have various other glute activation work (clam shells, bridges, complex bridges, hip stretches, glute stretches etc). I have had to reduce the squatting significantly whilst focusing on the training though, as it just takes too much out of me and I need a couple of days to recover. So the reduction in squatting may be partly to blame, however, until starting the VO2 max work I have had no issues with the knee outside of the normal careful management. Even now, it is only the VO2 max work that causes any issue. I rode outside tonight on my enduro bike, with a stuck on brake, and my knee felt better after riding than it did at the start, because I know how to focus on activating my glute in that leg.
@mcneese.chad - thanks so much for your input. I use my road bike on the trainer and I will be racing on my XC mtb in January…but I have always trained and ridden on a mix of bikes (roadie, hardtail, xc susser, enduro bike). I have ridden 1000s and 1000s of kilometers audaxing on the roadie which is now on the trainer so it’s not an unusual position for me. Although I appreciate I probably should have the XC bike on the trainer for the upcoming event, the fact is, I am very time pressed and it is far easier for me to have the roadie on the trainer and the XC bike always ready to ride outside. It makes more sense for me to get my XC bike miles in outside as I am still getting used to the tyres and I need constant reminding that I can’t throw it around like I do the big bike with big tyres or I end up on my arse
I have had a bike fit previously on the roadie, a long time ago, but I have since dropped my saddle (actually have on all bikes) since the meniscus injury to ensure better glute engagement. So I agree with you there @Weiwentg about lowering the saddle.
So as I say, it is only the VO2 max work that is triggering the knee pain. However, reading all the replies above, it sounds like I need to keep it in there. I will try a few things:
a)Turning off the ERG - thanks @HLaB for that suggestion.
b)Reducing cadence for the VO2s thanks @stonerider - I’m not sure I’ll manage them that low, but I can certainly reduce a bit. so I can concentrate on form more. I guess I can always turn down the intensity if I am struggling to muscle through it.
c)Videoing is a great idea, thanks @Brennus
In terms of why my technique is sloppy at higher cadence - I think it’s practice, or lack of it, at that kind of leg speed with flat pedals. I now run flat pedals on everything (for other special snowflake reasons I won’t bother going into) including my roadie, and I just haven’t ever done these kind of cadences with flats.
I’ll also add some squatting back in. Maybe this entire thread is just a good reminder that I need to prioritise the physio above everything, even FTP. Because if I am injured, FTP is totally irrelevant, isn’t it?