Bones: Responses to Training

Bones provide the structure onto which soft tissue is built, they provide protection for internal organs, as well as provide a system of levers that allow for movement by way of muscular contraction. Much like muscles, bones undergo changes and improvements when a training stimulus is introduced, namely: impact and weight bearing exercises.

Though there are many functions and mechanisms taking place within the bones, I want to focus on the two main things that are happening within the bones when training occurs. First is bone hypertrophy due to training, and second is bone density improvement due to training.

The periosteum, a soft membrane covering the outside of bones, is responsible for building new outer layers of bone onto the existing bone. It essentially builds concentric layers of new bone, and this building is more rapid when the bones are being regularly stressed by way of impact or weight bearing exercises. It should be noted, however, that bone hypertrophy is very minuscule even when training is introduced.

The second and most prominent mechanism of bone response to training is density improvements. There are two types of specialized cells within the bones: Osteoblasts and Osteoclasts. Osteoblasts are responsible for building new bone while Osteoclasts reabsorb bone tissue. When introduced to impact and/or weight bearing training, Osteoblast activity increases while Osteoclast activity decreases. This increased activity results in greater bone density. Conversely, when an individual is sedentary, the opposite occurs. Osteoclast activity increases while Osteoblast activity decreases, effectively causing bone wasting.

Why is this important? Who doesn't want stronger bones!? This is especially important for the performance athlete within impact/contact sports. Having greater bone densities makes the athlete less prone to bone breaks and stress fractures. Even the non-contact or non-weight bearing athlete, such as cross country runners, can benefit (Cross country runners can often suffer from stress fractures that occur due to the continuous and repetitive striking of the ground during long distance runs). Having these improved bone densities also helps the average individual avoid bone wasting which can lead to osteoporosis and stress fractures.

Moral of the story: Lift heavy, run, jump, and get active!