Perhaps there were differences in what was measured e.g. peak maximum, or maximum able to be sustained for a certain amount of time?
I can't find any info in Walitt et al. 2024 about exactly how they measured it. But I think maximum voluntary contraction is pretty standard.
It's the flipped results I can't get my head around - if Jäkel's subjects had the same sex composition as Walitt's (59% female), then the mean max hand grip for Jäkel's sample would have been 23.5. Walitt's group's mean max hand grip, however, is higher, 35.2. So you think, huh, OK, they were just a stronger group. But that's odd - Walitt et al. sought out moderate-severe patients, and their SF36PF scores would suggest they found them, with a mean SF36PF of 32, lower than Jäkel's 43. Jäkel's group contains many patients with high SF36PFs in the 60s, 70s, 80s and 90s.
It seems to me that hand grip strength is going to vary a lot between people regardless of ME/CFS. Things like hand size, prior training and lifestyle, maybe muscle cell type. When you are working with small samples of people, those differences could easily mask impacts of ME/CFS (or lack of impacts).
Indeed - it remains frustrating that after all that time, we ended up with a study with such a small sample that we can't be confident in negative findings.
I don't think ME/CFS has changed my peak muscle strength on a good day (except as a result of reduced physical activity). I think what it has changed is my ability to generate the same force repeatedly.
Yeah, that's what I notice in everyday life too - a disproportionate difficulty with repeated or sustained activity. (I'm severe though, with a possibly unrelated issue, so my strength is reduced.)
I saw a new doctor recently. I was determined not to just be dismissed as deconditioned and told to exercise. So when he told me to squeeze his fingers, I went for it. He yelped! It worked, though.
Editing to add:
Note: When I say "higher", "more" etc in these posts, I'm not talking about statistically significant differences, just numerical ones that might be non-negligible. I'm just trying to think out loud, brainstorm, not pronounce anything.