I like to train to heart rate and have done it succesfully in the past however recently I have been getting some unusual readings which do not match up to the perceived effort.
My maximum heart rate is ~197 and my resting heart rate is ~40, which according to various resources puts my sub threshold/marathon pace runs at 158-166bpm (75-80%HRR) and my easy runs at 134-142bpm (60-65%HRR).
In the past these HR intensities matched up very well to the recommended paces of an easy run and a marathon pace run however more recently hitting these HR levels seems to require far too much effort and the pace is far to quick, therefore I have been running to effort and the HR for easy runs has typically been 120-130bpm and for marathon effort runs 145-150bpm.(too low)
I have had a period of approximately 7 months of very interrupted training and inconsistency due to persistent injuries/niggles which has necessitated time out from running completely or running VERY low weekly mileages. During this time I have tried to maintain aerobic fitness by supplementing the small amount of running I have been able to do with spinning.
I am keen to start a base phase and I want to follow HR zones as per Hadd's recommendations but at present it requires far too much effort.
Does anyone have any ideas why? Could it be glycogen depletion (I run first thing in the morning on an empty stomach, though this didn't use to be an issue) or lack of specific adaptations in the muscles i.e good general aerobic fitness from spinning but no specific running fitness. Or could it be something else.
All thoughts/advice appreciated
TJ