Osteoporosis 101

Several physiological and anatomical changes occur within the human body as individual’s age. One of the most prevalent changes occurs in the musculoskeletal system. Bone mass declines with age similar to muscle mass. Bone mass peaks around 30 years of age and then gradually declines. The cause of bone loss is multifactorial, including inactivity, changes in hormone levels, and improper nutrition. In regards to physical activity, the age-associated decline in muscular strength parallels the loss of bone mass (1). Research shows a significant risk factor for osteoporosis is physical inactivity.

Osteoporosis is a chronic disease characterized by a thinning and weakening of bones (2). Osteoporosis is determined as having a bone mineral density more than 2.5 standard deviations below the young adult mean value (3). Once bone mineral density reaches such a low-level, any imposed stress or force may lead to a fracture.

The most common fracture sites for people with osteoporosis include the wrist, thoracic spine, and proximal femur. This is due to a greater proportion of trabecular bone, which is more fragile when calcium is lost. Here are some interesting statistics in regards to osteoporosis:

  • Approximately 10 million Americans over the age of 50 have osteoporosis.
  • Almost 35 million Americans over the age of 50 have osteopenia, which is a bone density lower than normal and can lead to osteoporosis.
  • 40% of Caucasian women will fracture a wrist, spine, or hip in their lifetime.
  • Almost 20% of hip fractures lead to permanent disability.
  • By 2020, half of all Americans over the age of 50 will be at risk for fracture due to weak bones (4).

As a living tissue, bone is constantly in a state of flux. Specialized bone cells called osteoblasts mediate the addition of calcium by adding to the bone matrix, and other cells called osteoclasts mediate the removal of calcium from the bone matrix. As we age, bone construction slows and bone degeneration accelerates, leading to osteoporosis. There are several risk factors for osteoporosis which include; history of fractures due to insignificant trauma, family history of osteoporosis, postmenopausal females, men over the age of 70, history of smoking at least one pack of cigarettes per day, and low body mass.

Unlike skeletal muscle, structural changes to bone tissue lead to very few functional decrements. That said health and fitness professionals must keep bone loss in mind especially when working with older adults who have Osteoporosis. To mitigate the loss of bone with age, older adults should engage in strategies that will have a protective effect on bone mass. The force of gravity imposes stress on bones. Gravity gives weight to an object due to the acceleration of that object toward the center of the earth. The force the skeleton is exposed to when absorbing ground reaction forces causes the skeleton to be loaded and will increase bone integrity and strength. Lifting weights will impose a stress to bone due to the articulation of the muscle, fascia, and bone.

According to research weight-bearing exercise with significant loading of bone helps to preserve bone mass in older adults (5). High-intensity resistance training with heavy loads relative to maximal strength also shows an increase in bone mineral density in older adults, while moderate intensity resistance training shows a smaller effect (6).

References:

  1. Burr DB. Muscle strength, bone mass, and age-related bone loss. J Bone Miner Res. 1997;12(10):1547-1551.
  2. Liu H, Paige NM, Goldzweig CL, et al. Screening for osteroporosis in men: a systematic review for an American College of Physicians guideline. Ann Intern Med. 2008;148(9):685- 701.
  3. Kanis J, Melton LJ, Christiansen C. et al. The diagnosis of osteoporosis. J Bone Miner Res. 1994; 9: 1137-1141.
  4. Center for Science in the Public Interest. Nutrition Action Health Newsletter. 2005;32(3)., Centers for Disease Control and Prevention, 2008.
  5. Kelley GA, Kelley KS, Tran ZV. Exercise and BMD in men: a meta-analysis. Am J Phys Med Rehabil. 2001; 80: 65-77.
  6. Cussler EC, Lohman TG, Going SB, et al. Weight lifted in strength training predicts bone change in postmenopausal women. Med Sci Sports Exerc. 2003; 35(1): 10-17.

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