Spin class (25 DAYS UNTIL RUN4KIDS!!)

I went to spin this morning before work (after taking Bella for her usual trot around the park) then rode my bike to work. After fiddling with my heart rate monitor limits the other day I really struggled to get my heart rate into any sort of anaerobic/ aerobic zone- previously my 65% limit was 122 bpm, but now it is 138! At spin class I have to work so hard to get my heart rate to budge, it really wants to hang around 110 and I have to try so hard, mess around with the resistance and pace to get it up into a zone where my heart will be working- so now it is even harder! I know that nothing has changed, just the silly numbers on my watch, but it still messes with my head when I am struggling to work up a sweat.
My max heart rate was only 76% and my average was 57%- though the ride to work has some easy flat sections and finishes off with a fantastic gradual downhill and my heart rate would back off a lot.
Anyway, glad to be back at work after two more days re-training in certain aspects of work that apparently require six monthly updates.