The bones in our body provide a framework for support that every skeletal muscle, tendon, and ligament attach. Without this framework, we could not stand, walk, run, jump, etc. Our skeletal system also provides protection for the vital organs of our body: heart, lungs, etc. Various minerals such as calcium and lipids are stored in skeletal bones.
The bones of our body are made up of two types:
- Cortical bone (compact bone) – this is the outer most layer of the bone that is dense, but does have a few small opening for mineral deposits.
- Trabecular bone (spongy bone) – the inside of the bone that is spongy and has a honey-comb appearance. The spaces between this “web” are filled with bone marrow. The bone marrow is made of lipids and where the blood cells (red blood cells, white blood cells, and platelets) are produced.
The body is divided into two main types of skeletons: axial skeleton and appendicular skeleton.
- Axial – the bones of the skull, spinal column, ribs, and sternum
- Appendicular – pelvis, shoulder girdle, upper and lower extremities (arms and legs).
Our bone density is mainly determined during our peak growing years (adolescence) and into early adulthood when peak bone mass occurs. Research has shown that being physically active during these times positively affects peak bone mass later on as we age.
Bone density is critical to prevent osteoporosis. Osteoporosis is the thinning of the bone over time causing the bone to weaken and increase the likelihood of fractures. Exercise along with diet, play a significant role in the maintenance of bone density.
Exercises that stress the muscles, tendons, and ligaments of the body (weight lifting, strength training, running, etc.) produce stress and force upon the bones. These forces are what cause the bones to adapt and become denser. The force “bends” the bone stimulating bone cells (called osteoblasts) to lay down collagen to fill in spaces on the outer layer of the bone (cortical bone). Over time the collagen becomes mineralized as calcium increasing the thickness and density of bone. The following video (4 minutes) explains how the body builds bone:
While exercise is great for bone density, not all exercise is created equally in terms of bone stimulation. For the bone to be stimulated, there has to be enough force generated on the bone to produce the adaptation needed. While walking is a great activity, it will most likely not produce enough force since your body is used to walking. Higher impact activities would be needed to produce enough force (running, high impact aerobics classes, strength training). Low impact aerobic activity (swimming, cycling, elliptical, etc.) do not provide a big enough stimulus because the body is supported.
Strength training provides the best route for increasing bone density as long as the following principles are applied:
- Select exercises that are multi-joint and use as many muscles as possible.
- Use single joint, isolated exercises minimally.
- Choose exercises that direct forces through the hip and spine (osteoporosis is very common in the spine and hips).
- Use a weight that you can control that causes muscular fatigue for no more than 10 reps.
- Make sure you are adequately warmed-up by performing your foam rolling and mobility exercises.
Strength training can be a very empowering activity to not only improve bone density and strength, but increase confidence as well. Nothing feels better than being strong and able to lift something heavy with ease. It allows your body to do what you do, but better and with more efficiency. Strength training has a cross over effect to just about anything in life, recreation, and sport. Some other benefits of strength training include the following:
- Increased strength
- Increase in power output
- Helps improve balance and stability
- Increases HDL’s (good cholesterol)
- Decrease blood pressure
- Slight improvement in aerobic capacity (~4-5%)
Never done strength training before? Hire a personal trainer or do online training. These resources can provide you a great understanding of how strength exercises are done so you can feel confident you can perform them with correct technique.
authored by Dave Radin, BS, CSCS