Muscle mass decreases at a rate of 3–5% per decade beginning in the third decade of life, with an accelerated rate of decline after age 60, leading to reduced physical function.

Study: Low Lean Mass Predicts Incident Fractures Independently From FRAX: a Prospective Cohort Study of Recent Retirees

This study found that older adults with less muscle are much more likely to break a bone, even if their bones seem strong. This supports the idea that losing muscle as we age makes us weaker and more prone to injury.

Study: Prognostic significance of preoperative respiratory sarcopenia for functional recovery after cardiovascular surgery.

This study found that older patients with weaker breathing muscles had a much harder time moving and recovering after heart surgery, showing that losing muscle strength makes it harder to stay physically active — just like the claim says.

Study: The Influence of Aging on Hip Abductor Muscle Torque, Power, Velocity and the Association With Lower Limb Physical Function

This study found that older people have weaker hip muscles than younger people, losing about 3–5% of strength every 10 years after age 30, and that this weakness makes it harder to do everyday tasks like standing up or climbing stairs.

Study: The role of protein quality and amino acid composition in preventing sarcopenia and functional decline in older adults

This study says older people naturally lose muscle and strength as they age, which makes it harder to move and stay independent — exactly what the claim says. It doesn’t give the exact 3–5% number, but it confirms the loss is real and serious.