@nycmusic, Yes, this is largely true. That said, bone tissue responds to mechanical stress through a process called "Wolff's Law," which means that bones adapt and become stronger when the muscles pull on them during weight-bearing or resistance exercise.

When you lift weights, the contraction of the muscles places stress on the bones at their attachment points, which the signals bone-forming cells to maintain or increase bone density. Because the body adapts to repeated stress, continuing to use the exact same weight eventually provides less stimulus to the bones.

Gradually increasing the challenge over time (progressive overload) helps to maintain that stimulus so bones continue to receive the strengthening signal. This progression doesn't mean lifting very heavy weights; it can include modest increases in weight, additional repetitions or sets, greater resistance from bands, or more challenging movements that load the vulnerable areas - the hips, spine, and legs.

For those of us with osteoporosis, the most important factors are consistent weight-bearing and resistance exercise performed with good form and safe spinal alignment, with gradual progression rather than aggressive increases in load - but the load does need to increase over time.