stefan_berlin said:

Body composition tracking via bioimpedance on lean mass (InBody scan every 3 months): Metric Baseline Month 3 Month 6 Month 9 Skeletal Muscle (lbs) 69…

Saving this. It is the first explanation that did not require me to already understand it. Sending this to two other people who asked me the same thing last week.

Clinical perspective, offered as context rather than as advice.

Back pain as a lean mass side effect: not from the medication itself, but from rapid body composition changes. Losing 53 lbs shifts your center of gravity and your core muscles need time to adjust.

Physical therapy has been essential. Core strengthening exercises (planks, dead bugs, bird dogs) daily for 10 minutes have eliminated my lower back pain. Your body is literally relearning how to carry itself.

Dr.KarenChen ↑ said:

Back pain as a lean mass side effect: not from the medication itself, but from rapid body composition changes.

Same experience, arrived at from the opposite direction. Nothing to add that would improve it.

Dr.KarenChen ↑ 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].