lessthanhalf said:
Strength and muscle mass usually go hand in hand, though the link isn't absolute. Long-term manual labor or training with lighter loads can produce muscles far more powerful than their dimensions would suggest — think of the older man with modest muscles who can lift a surprising amount.
Tirzepatide has been found to lower intramuscular fat and boost muscle efficiency by roughly 6%, which may partly offset the drop in muscle mass that comes with weight loss.
Where you start from matters. With severe obesity, muscle loss tends to track the overall weight reduction, and day-to-day physical function almost always improves, because no longer hauling that extra mass delivers a bigger functional gain than the muscle lost. Anyone who has climbed stairs after dropping weight knows this vividly. Obesity itself usually comes with added muscle — partly from the generally pro anabolic state it creates, partly because moving a heavier body demands more muscle — so shedding some or all of it carries little real cost. Those who begin with low muscle strength, typically the elderly or chronically ill, face the greatest risk of sarcopenia from GLP drugs, since losing muscle mass and strength there could harm physical abilities.
Optimising strength and muscle mass while pushing body fat below the normal weight range is a rather different problem. I've read many posts here from people who say they gained lean mass and lost fat through heavy exercise plus a near calorie-balanced diet while on GLP's, but I can't really judge how easy or difficult that is.