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Writer's pictureAlyssa Okun

Bones: They Don't Just Hold You Up!

Updated: Jun 25


Published October 31, 2020


More Than Just A Scaffold! Why Bones Are Important

Bones serve many important purposes in our body, and they are key in allowing us to perform our daily functions as well as maintain our health.

Support: One of the most well-known functions of bones is the support they provide to our body. They provide the rigid structure to hold up and support our soft tissues – organs, muscles, nerves, and blood vessels. And while bones are incredibly strong, they are also lightweight, which is an important feature as it allows our bodies to move sufficiently. Pound for pound, bones are 4 times stronger than concrete, and as strong as steel but 50 times lighter. Our bones make up only 14% of our body weight, as they are essentially hollow.

Mobility: Bones allow us to move by providing sufficient support and strength for muscles to contract. Muscles attach to bones via tendons, and bones serve as the levers that muscles move, while joints serve as pivot points. By acting as levers, bones can change the magnitude (strength) and direction of forces generated by muscles.

Organ protection: Bones provide protection to our internal organs, including our brain by the skull, our spinal cord by our vertebrae (spinal bones), our heart and lungs by our ribs, and our reproductive organs by our pelvis, to name some of the most vital ones.

Blood cell regeneration & maintenance: Bone is made of two types of bone: Compact bone, and cancellous, or spongy bone. Compact bone is more solid, harder and stronger, and is located on the external surface of the bone. Cancellous bone is very porous, more light-weight, and is located on the inside of the bone. Cancellous bone contains red bone marrow, which is what produces blood cells. In fact, most blood cells (red, white, and other blood elements) are created in bone marrow. Bones that have the highest concentration of red marrow are the spine, sternum (breastbone), ribs, pelvis, and small parts of the upper arm and leg.

Storage and release of minerals into body when needed: Bones act as a reservoir for minerals. Bones store 99% of the body’s calcium, and 85% of its phosphorous. Appropriate blood calcium level is important for proper bodily function, including muscle and nerve function, and bones can release calcium into the blood in times of need, such as pregnancy. Bones also store lipids (fats) as energy reserves in areas filled with yellow marrow (cancellous/spongy bones).

Bones Are Alive! Bone Remodeling

We have over 300 bones at birth, however as we mature, some of our bones fuse together so that as adults, we only have 206 bones. Bones go through a process called remodeling, in which a small amount of bone on the interior of the bone (trabeculae) is removed and then replaced at the same site. Remodeling occurs continuously throughout our lives, and most of the adult skeleton is replaced about every 10 years – that is, old bone breaks down and new bone is formed. Remodeling does not change the shape of the bone, but it is vital for bone health for several reasons. It repairs damage to the skeleton that can occur as a result of repeated stresses, such as small cracks or deformities in areas of cell damage. It prevents accumulation of too much old bone, which can lose its resilience and become brittle thus rendering it more susceptible to fracture (breaking). Remodeling also is important for its role in how the body stores and releases minerals. Bone is broken down (a process called resorption) to supply needed calcium and phosphorous when there is a deficiency, such as in our diet, or with increased needs, such as during pregnancy. When there is ample calcium and phosphorous, bones can take up these minerals and restock their reserves, through the formation phase called remodeling.

There are 3 main types of cells involved in the remodeling of bone: Osteoblasts, osteocytes, and osteoclasts. Osteoblasts are cells that help produce bone. Osteoblasts lay down bone in orderly layers that add strength to the matrix. Osteocytes are cells derived from osteoblasts that are buried in the bone matrix, and they are the most numerous cells in bone. Osteocytes form extensive communication networks and are crucial to the ability of bone to respond to mechanical forces and injury. Osteoclasts remove bone by dissolving the mineral and breaking down the matrix in a process called bone resorption. Excessive bone breakdown by osteoclasts is an important cause of bone fragility not only in osteoporosis, but also in other bone diseases such as hyperparathyroidism and Paget’s disease.


Osteoporosis: You Can Overcome It!

Osteoporosis literally means porous bone. Osteoporosis occurs when the creation of new bone doesn’t keep up with the loss of old bone. In osteoporosis, bones become less dense and their quality is reduced, which causes them to become thin and weaker, leading to increased risk of fracture, or breaking. According to the Osteoporosis Foundation, around the world, 1 in 3 women and 1 in 5 men over the age of fifty will suffer a broken bone due to osteoporosis. Fractures due to osteoporosis most commonly occur in the hip, spine, and wrist.

A Bone Density Test is a screening tool that uses x-rays to measure how much calcium and other bone minerals are in a segment of bone. If you are over 65 and/or have increased risk of osteoporosis, you should have a bone density test to determine your bone health. Increased risk factors include both non-modifiable (not able to change), and modifiable (can be changed). Non-modifiable risks include sex – women are more likely to develop osteoporosis than men, age – increased age increases risk, race – people of white or Asian descent are at increased risk, family history, hormonal levels, and body frame size – small frames tend to have increased risk, possibly because they have less bone mass to draw from as they age. Modifiable risk factors include diet, steroid use, and lifestyle – activity level (more is better), alcohol and tobacco use – regular use of these can increase risk of osteoporosis. Bone density test results are reported in two numbers: T-score and Z-score.

· The T-score is your bone density compared with that expected in a healthy young adult of your sex. A score of -1 and above indicates that your bone density is normal. A score between -1 and -2.5 is a sign of osteopenia, in which your bone density is below normal and may lead to osteoporosis (pre-osteoporosis). A score of -2.5 or below indicates that you likely have osteoporosis.

· The Z-score compares your bone density to the average bone density of people your own age and gender. If your Z-score is more than 2 standard deviations below other individuals your age, talk to your doctor about other medical conditions or medications that may be causing lower than expected bone density.


Osteoporosis is treatable and often preventable. Below are tips to prevent the development of or improve the condition of osteoporosis:

· Eat a healthful diet that includes sufficient calcium and protein, which are key nutrients for bone health

· Get enough Vitamin D, as it helps with the absorption of calcium and phosphorous. Vitamin D is made in the skin after exposure to sunlight, can be found in some foods including oily fish, eggs, mushrooms, and fortified dairy food or juices, and is available in supplements

· Maintain a healthy body weight, as being too thin (BMI < 19) can increase risk of low bone density

· Stay active – regular activity and exercise that involves weight-bearing and resistive strengthening improves bone density

Broken Bone? Not All Is Lost! Bones Can Actually Heal Very Well

Though bones are stronger than steel, they can break if a strong and fast force is applied, due to their light and flexible nature, or due to other conditions, such as osteoporosis. However, bones are considered a highly vascularized connective tissue, meaning that they have a rich blood supply. Tissues that have a good blood supply, such as skin, muscles, and bone, tend to heal faster than tissues with a poor blood supply, such as tendons, ligaments, and cartilage. The skeletal system receives 10-15% of the body’s total cardiac output. Blood supply in bones plays a significant role in bone development, regeneration, and remodeling. Blood vessels supply bones with oxygen and nutrients, remove metabolic waste, and provide hormones, growth factors, and neurotransmitters that are secreted by other tissues.

If you suffer the unfortunate experience of a bone fracture, exercise can help with your recovery, though it is important to provide sufficient immobilization and rest of the fracture site to allow for tissue healing, and to abide by the recommendations of your orthopedic doctor. Bones heal in about 6-12 weeks, depending on the location and severity of the break. Exercise, especially cardiovascular exercise, increases circulation of blood throughout the body, as well as contributes to bone release of calcium and ATP (adenosine triphosphate, a compound that provides energy to drive many processes in living cells), both important in bone formation. Additionally, low-intensity weight-bearing exercise has been demonstrated to help the healing response in bone repair, again, depending on the time-frame from injury, type of injury, and other recommendations from your orthopedist. Depending on where your fracture is, there are still ways to be creative with both cardiovascular and strengthening exercises that don’t involve the broken part, such as core exercises lying down, light strengthening of the non-affected limbs, and cardiovascular exercise (walking, stationary bike if upper extremity injured; seated arm circles if lower extremity injured). Working with a physical therapist, such as myself, can assist you in rehabilitating the injured body part safely, progressing appropriately through the tissue stages of healing and functional recovery, and helping to maintain overall physical health as your body heals.


Make Yourself Better! Best Way to Build Healthy Bones

Exercise isn’t just good for your brain, it’s good for your bones! As discussed above, like muscle, bone is living tissue that responds to exercise by becoming stronger. Weight-bearing and resistance exercises are the best types of exercise to promote bone density.

Weight-bearing exercises, or external bone loading stress/forces, cause compressive forces on your bones due to gravity and/or impact. For the lower body, weight-bearing exercises include walking, hiking, jogging, climbing stairs, dancing, and jumping activities, such as jumping jacks, which can also improve bone density in the spine. For the upper body, weight-bearing exercises include push-ups and planks. Higher impact activities such as jogging or jumping rope increase the weight on bones, providing more bone-strengthening benefits, though you should avoid high-impact exercises if you have osteoporosis or another condition that leads to bone thinning. Tai chi and yoga (which involves weight-bearing in both the upper and lower body), are examples of weight-bearing activities with low to no impact.

Resistive exercises, or internal bone loading stress/forces, cause forces on bone from contracting skeletal muscle. The pulling force where the muscles’ tendons attach to the bone stimulates bone generation. Resistive / strengthening exercises include lifting weights or using resistance bands, and exercises that involve controlling your own body weight, such as pull-ups. Squats & lunges (lower body) and dips (upper body) are examples of exercises that are both weight-bearing and resistive. A physical therapist can help you not only determine which exercises are weight-bearing and/or resistive, but also which are the best types of exercises for you based on your history and current level of ability, and how to progress appropriately as you get stronger.











References:

1. https://kidshealth.org/en/parents/bones-muscles-joints.html#:~:text=Bones%20provide%20support%20for%20our,the%20shape%20of%20the%20face.

19. https://orthoinfo.aaos.org/en/staying-healthy/exercise-and-bone-health/

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