Dr.PulmRoch said:Back pain as a lean mass side effect: not from the medication itself, but from rapid body composition changes.
Muscle fiber type changes during GLP-1-mediated weight loss, relevant to lean mass: preliminary biopsy data suggests that weight loss shifts the skeletal muscle fiber type distribution:
- Decreased Type IIx (glycolytic, fast-twitch) fibers
- Increased Type I (oxidative, slow-twitch) fibers
- Improved mitochondrial density and function
- Enhanced insulin-stimulated glucose uptake per fiber
This "metabolic remodeling" of muscle may contribute to improved insulin sensitivity independent of total lean mass changes. The muscle you keep becomes metabolically better, even if there's less of it[1].
[1] Pirkmajer S, et al. Front Physiol. 2023;14:1123456.