Weight training affects more than just muscles; it can also strengthen your bones! As we age, bones begin to lose mineral density (Bone Mineral Density - BMD), and they becoming slightly weaker as a result; this is particularly evident in postmenopausal women. This condition is commonly known as osteoporosis. This decrease in BMD can be of concern, as weaker bones are at an increased risk of bone fracture.
Longitudinal studies have shown that appropriately prescribed progressive resistance training can stimulate bone growth and increasing BMD in older adults, reducing risk of fracture. We know that tissue responds to stress by adapting and rebuilding stronger. This is true of muscles and ligaments, but it is also true for bones! Mechanical loading (stress from external forces, e.g. lifting weights) of bones stimulates the migration of cells called osteoblasts (bone-building cells) to lay down collagen proteins, strengthening the bone over time.This growth increases bone diameter and strength, increasing the load tolerance of bone.
Resistance exercises stimulate the strengthening of bone at the tendon junction by causing the muscles to pull on their bony insertions. Together, these adaptations allow bones to become more resilient to these stresses in the future. In order to stimulate this adaptive response, bones must be loaded in the appropriate direction with an appropriate load. Band exercises, for example, do not stimulate bone development because they are not providing a compressive force on the bone. According to the National Strength and Conditioning Association, a combination of progressive overload, axial loading (weight bearing), and exercise variety have been shown to best stimulate bone formation. Consult with a fitness professional to open a conversation about bone health, and to make a plan for appropriate resistance training.
Watson, S. L., Weeks, B. K., Weis, L. J., Harding, A. T., Horan, S. A. and Beck, B. R. (2018), High-Intensity Resistance and Impact Training Improves Bone Mineral Density and Physical Function in Postmenopausal Women With Osteopenia and Osteoporosis: The LIFTMOR Randomized Controlled Trial. J Bone Miner Res, 33: 211-220.