“Just as lifting weights helps maintain muscle size and strength, weight-bearing exercise stimulates bones to become denser and stronger. One of the causes of bone loss, like muscle loss, is lack of use; therefore, weight-bearing exercise such as walking, running, and aerobic dance can increase peak bone mass, prevent bone loss, and therefore reduce the risk of osteoporosis. Exercise can also benefit individuals with arthritis because the strength and flexibility promoted by exercise help arthritic joints move more easily.”
Did you ever wonder, why would someone exercise in space? Why astronauts in the international space station exercise on a regular basis? Or rather, why after a prolonged stay in space some astronauts lose bone mass? Well in order to address such issues, we need to address bone tissue characteristics.
Bone tissue is composed of bone cells. There are three types of bone cells: “Osteoblasts”, “Osteoclasts”, and “Osteocytes”. Simply put, Osteoblasts build bone, and get trapped in a chamber called “lacunae“, and become osteocytes. Osteocytes, have extensions in order to communicate with other osteocytes trapped in other lacunaes. So, every time bone senses weight on it, it stimulates the osteocytes, which will in return stimulate the osteoblasts. Osteoblasts, once stimulated, initiate bone building, and bone matrix (mass) increase. The function of osteoclasts, is to degrade bone whenever necessary.
In space there is no gravity, no weight sensed by bone. The osteocytes cannot be stimulated, and initiate bone building by osteoblasts. In order to do so, and avoid the loss of bone mass, they need to exercise. This is also relevant to a lack of exercise on earth, a lack of exercise will reduce bone mass as well. A loss significant enough to cause health problems. Any thoughts?
Dr. Zachary Lahlou