The Effects of Exercise on Joint & Bone Strength

The Effects of Exercise on Joint & Bone Strength

The joints of our body are composed of two or more bones joining together, along with the muscles, tendons, cartilage, synovium and ligaments that hold the whole structure together. The shape of our bones reflect the forces applied to them. For example, small bumps, ridges and other features on the surface of our bones are the attachment sites for tendons. When muscles are put under more load through activities, stress or exercises, the corresponding attachment sites enlarge to withstand the increased forces. Bones that are under more stress become thicker and stronger, while in contrast bones that are not subjected to ordinary stresses tend to become weaker, thin and more brittle. Wolff’s law, developed by anatomist & surgeon Julius Wolff in the 19th century, states that “bone in a healthy person or animal will adapt to the loads under which it is placed.”

Regular weight-bearing exercise is an important component for maintaining healthy bone structure. Avid weight lifters often have thick bones with very prominent ridges. Non-athletes or those who have little to moderate amounts of physical activity will find weight-bearing activities are imperative for stimulating normal bone metabolism of maintenance as well as maintaining bone strength.

Changes in bones of the skeleton can take place in relatively short periods of inactivity. For example, someone uses crutches to take weight off an injured leg while they wear a cast. Within a few weeks, the unstressed bones can lose up to a third of their mass. When normal weight loading resume the bones rebuild. However, it takes longer to rebuild bone than to lose bone density. The removal of calcium salts can be a serious health hazard for long-term bedridden patients or paralyzed individuals who cannot put normal stress on their skeleton.

Bones of the skeleton become thinner and weaker as a normal part of the human aging process. Inadequate ossification is called osteopenia. Everyone of us usually become slightly osteopenic as we age. Bone mass reduction begins between ages 30 and 40. Around this age, osteoblast (bone building) activity begins to decline, while osteoclast (bone breakdown) activity continues at the previous level. Women tend to lose about 8 percent of their bone mass every decade. Men often lose less, but around 3 percent per decade. The epiphyses or ends of the long bones, the vertebrae of the spine, and our jaws lose more bone mass than other locations. Side effects of low bone mass are more fragile limbs, loss in height, and sometimes the loss of teeth.

Osteoporosis is the further reduction in bone mass that inhibits normal functions. Bones become fragile and brittle making them more likely to break when exposed to stresses that healthier individuals could easily adjust to. This can be seen when an elderly person can suffer a hip fracture when simply attempting to sit or stand. A loss of mobility, independence and consequently self-confidence can occur when fractures result in older individuals leading to further weakening of the skeleton as they become less active and fearful of future injuries.

Hormonal balances are important in maintaining bone deposition. If and when hormone levels decline, bone mass also declines. After age 45, about 29 percent of women and 18 percent of men will develop osteoporosis. With women the condition increases after menopause, from a decrease in estrogen production. Men in the same age group tend to have less severe osteoporosis due to continued production of testosterone into their later years of life.

Osteoporosis can sometimes develop into the secondary effect of many cancers. Cancers within the bone marrow, breast cancer, and other tissues release a chemical called osteoclast-activating factor. This chemical increases the number and activity of osteoclasts and produces severe osteoporosis.

By engaging our bones with strategic trauma exercise methods (or specific stress without injury) that can be regulated by the individual to make bones stronger and prevent osteopenia and/or osteoporosis. These types of exercises fall into 3 different categories of tension, impact and vibration exercises. Ironically, while some of these methods improve bone and muscular strength, they sometimes can cause pain and injury to the same joints that the individual might be trying to strengthen. Fox example, jumping rope, hiking and tennis might cause more injury to a 60+ than the benefits that might be gained from these practices.

Reference(s):

1. Martini, F., Nath, J. L., Bartholomew, E. F., Ober, W. C., Ober, C. E., Welch, K., & Hutchings, R. T. (2018). Fundamentals of anatomy & physiology. New York: Pearson Education.

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I have learned, studied, practiced and teach literally hundreds of various low-impact exercises that can build stronger bones, muscles and joints. Private, small or group instruction.

Be well!

Jim Moltzan

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