Bone Tissue and Bone Health

Bone is not inert scaffolding; it is living, dynamic tissue that is continuously broken down and rebuilt in a process called remodeling, carried out by osteoclasts (which resorb bone) and osteoblasts (which form it). Bone consists of a dense outer cortical (compact) layer and an inner trabecular (spongy) lattice, a protein matrix (mainly collagen) mineralized largely with calcium and phosphate.

Bone adapts to the loads placed on it: mechanical stress from weight-bearing activity and resistance training stimulates bone formation and increases or maintains bone mineral density, while disuse (immobilization, sedentary living, weightlessness) leads to bone loss — an application of the specificity/overload idea (see specificity). Bone mass typically peaks in early adulthood and declines with age; insufficient density leads to osteopenia and osteoporosis, raising fracture risk (see osteoporosis). Nutritionally, bone depends on adequate calcium (see calcium) and vitamin D (see vitamin-d, which governs calcium absorption), among other nutrients. Weight-bearing, impact, and resistance exercise are central non-pharmacological strategies for building and preserving bone.

• Bone is living tissue, continuously remodeled by osteoclasts (resorb) and osteoblasts (form).
• Structure: cortical (compact) outer layer + trabecular (spongy) interior; collagen matrix mineralized with calcium/phosphate.
• Responds to load: weight-bearing/resistance exercise builds density; disuse causes loss.
• Peak bone mass in early adulthood, then age-related decline → osteopenia/osteoporosis.
• Calcium and vitamin D are key dietary supports for bone.

• calcium, vitamin-d — key nutrients for bone mineralization.
• osteoporosis — low bone density and exercise considerations.
• specificity — bone adapts specifically to imposed mechanical load.