I have a stable exercise routine, stable diet, and stable everything else I can think of. Yet, within short amount of time, specific exercises muscle endurance drops wildly (and sometimes goes back up slowly).
Example: calf raises on one foot, from heel down to full extension, warmed up but fully rested - my left calf, I used to be able to do around 25-30, but very quickly, within 10 days, this dropped to 10-15. For no reason I can think of.
This is just an example, it can happen at any time with any muscle group.
When I observe during the repeats what happens seems to be, the "burn" period is gone. That is, used to be there is an extended period where I can feel my muscles progressively burn and burn more, until I can't repeat. But when the "drop" happens, then there is no "burn" period anymore, I do repeats fairly easily, and then suddenly, I can't do any more.
Is this just because, a human body is not a machine and I should just not worry about it. Or is this an indication I am doing something wrong, diet, exercise, or whatever, perhaps something going wrong with my body??
I understand you may say, add X to your exercise, or something like that. This is not really what my question is. I like my routine, and it is stable and so I don't understand why there should be such drops in the first place. There shouldn't, not as fast anyway. I want to know why.