Probably the most dispiriting session of cycle training I've done for a long time, it couldn't really have gone any worse. I felt that it was going to be a difficult session which I was ready for but I just didn't feel physically up to this session at all and felt tired from recent hard (by my standards) sessions before I even started.
Anyway, I started off and my HR rose to the required level (about 88% MHR) when I was pushing out about 320W. I found this level of effort (88%-92%) completely unsustainable and I had to ease right off after only 10 minutes, I was unable to keep the effort on. I think the idea of doing 2x20 minute efforts at this intensity is a long way out of my reach at the moment, it is not something I've trained for.
Rather than waste the session I continued with my ride at a lower effort level and rode at about 80%-84% of MHR for the remainder of the session which I could cope with, this was at a power output of 250W which was lower than I would have expected for this HR.
It seemed to me that at the unsustainable effort level I was above one threshold or another as my respiration was also becoming very ragged. I was a bit surprised and disappointed that I could not work at this level of effort as I thought I might have been able to manage it but this was too much for me at this stage.
Need some sleep now and I need to think over quite carefully what I'm trying to achieve.