Hi - I think I understand the confusion, too, at least I have similarly contradicting muscle-strength sensations and experiences.
I think the term 'weak' in my case is not helpful and prefer 'quickly exhausted'.
My first rheum. sent me first to get muscles/nerves as well as hormones/blood checked.
The neuro did EMG amongst other tests on me, too.
The EMG Included jabbing an electrode in my quadriceps whilst I had to clench it as hard as possible.
For those who haven't had the fun, it's like being told to keep your hand on a hotplate for 30-60 seconds
and if it's not flat on it you are told to flatten your hand... Docs know what it's like, because they have to do it just for that as part oft their studies.
It is mainly to check if the nerves are telling the muscles what to do properly, but in the process the muscle strength is tested, too,
as several docs told me afterwards.
But it then confused me when a few weeks ago a doc said my arm muscles need to be strengthened.
When I feel up to it I do gym and when I'm pretty OK I can put exactly/almost the same weights on as 5 years ago.
When I'm not but still want to keep at it, I put on less weight and do more repetitions, if poss.
To try to solve this confusion I said to the rheumy professor in the clinic I can do 30 press ups - how come someone says my muscles are weak?
He laughed and ironically said I should go up to 50, and then added, it's not HAVING weak muscles,
but trying to get them even stronger can help against the FEELING of weakness.
I still don't necessarily agree. When I started weight training about 10 years ago I went from strength to strength, but then I reached a plateau.
Now my muscles are still much stronger than most people training next to me or when I ride my bike.
But on bad days I can only spurt for a few minutes then need a break because I feel weak. Arms even more than legs.
But even legs: I can spurt full speed on the bike, take it down and up again, but to get off I have to wait a minute to have the 'strength' to do it. And then I try clambering two sets of stairs and think (as do people who see that): where is my muscle strength now?
Or I try to keep at exercises or qi gong with other fibro-patients or stretching with 70/80year-olds and get so strong fibro-ache and cramps that I have to cry.
With all this, I'm keeping at it and getting the hang of the sweet spots. In these exercises I have to go down to a third to a half of what the others are doing, by breaks, and doing it less intense. On my bike I use and enjoy my energy-bursts and overtake everyone else,
but instead of doing that until the weariness / exhaustion sets in, often after 3 or 4 minutes, I do it only for 1 minute, then settle down to a more moderate speed using as little muscle energy as possible and keeping that running.
Same swimming - if I pressure the muscles to full speed then I won't last 5 minutes and the ache and exhaustion will stay praps for hours,
but if I go for the least water resistance I can still swim fast enough, but keep going more. Here the first stroke of a length will do, or the push off, as a burst, after that I go in to my current maintenance mode.
I think "weak" is not helpful for my condition, dunno about yours. Others are confused, because they see I am strong one minute and weak in the next, and altho I am feeling weak. And I myself don't want to see it as being weak, but as exhausted, it sounds and fits better, helps me.
Yes, keeping on moving, keep trying different types of movement which may be more suitable in the current condition.
But I don't think that movement and exercise will make the feeling of strength come, when they are exhausted.
After a cold shower or even more whole body cryo my full or almost full strength is back for a time, minutes, hours or sometimes days.
