Peak and decline
Bone mass peaks around age 30 and muscle mass declines roughly 3–8% per decade after 30 unless it is loaded. This drift, not age itself, drives most later-life frailty.
What builds them
Resistance training two to three times a week signals bone to remodel and muscle to grow. Weight-bearing impact — walking, stairs, hopping — adds bone stimulus that swimming and cycling don't.
The nutrient trio
Adequate protein (about 1.2–1.6 g per kg for older adults), calcium (roughly 1000–1200 mg daily) and vitamin D are all needed. Protein without loading, or loading without protein, both underperform.