Bone given sufficient nutrients and hormonal support has long been known to gain strength in response to applied, controlled loading, such as weight-bearing exercise within the tolerance of the existing structure, one theory being that the loading generates a slight difference in electrical charge separation in the more loaded areas compared to the less loaded ones , a "piezoelectric effect" demonstrable in dry bone but harder to measure in living tissue but certainly plausible, with the orientation of bone structure growth in such areas making such loads easier to bear. Weightlessness on space missions and immobility here both lead to loss of such strength, and injury requires remodeling under appropriately oriented stresses to restore such strength. Bone density alone is a shakier marker for bone health, definitely correlated in most healthy people but not necessarily, with the denser, weaker bone sometimes seen when people tried large doses of fluoride to strengthen bone in years past or in congenital bone disorders, such as osteopetrosis. Women athletes training to the point of amenorrhea clearly lose bone density, even in well-stressed areas, and major nutritional problems in men or women can overcome any benefits of training. There is more and more evidence that NSAIDs such as ibuprofen, etc., may interfere with healing after acute injury. Anyway, bone health probably is less "either or" than "both and," with lots of things at play.