however, that increased physical activity can decrease inflammation and increase bone mineral density. A recent meta-analysis of 43 studies reported that physical exercise results in increased bone mineral density and a decreased risk of fracture in postmenopausal women. These findings suggest that exercise is important for both the prevention and treatment of osteoporosis (Howe et al., 2011). Osteoarthritis Women over age 50 in the U.S. have a 9.8% prevalence of arthritis of the femur, 11.6% have arthritis of the lumbar spine, and 16.5% have arthritis of either the femur neck or lumbar spine (Frontera, 2017). In general, these statistics show a higher prevalence of osteoarthritis in women over age 50 than compared to 15 years ago (Frontera 2017). The prevalence of low bone mass ranges from 36% to 53% of women, which is slightly higher than that found with men (Frontera 2017). Intramuscular fat and bone function Intramuscular fat may also impair bone function. Increased rates of intramuscular fat are associated with an increased risk of hip fracture, independent of bone density (Lang et al., 2010). Aging is known to result in a decrease in bone mass by 0.5% after age 40 and by as much as 2% to 3% in women after menopause (Concannon et al., 2012). Although osteoporosis is more common in women, it can also occur in men and is frequently underdiagnosed in this population (Lambert et al., 2011). Men are less likely to have osteoporosis but are more likely to experience complications and even death following a hip fracture. Lambert et al. (2011) found that men are more likely to experience subsequent fractures and are less likely to return to independent function than are women who experience hip fracture. Therefore, while osteoporosis may not occur as often in men, it is still a significant problem. Effects of bedrest on the musculoskeletal system As little as five to seven days of bedrest in healthy older adults results in a decrease of lean mass in the leg by 3% to 4% (Reidy et al., 2017). If healthy older adults suffer such a rapid loss of muscle mass with decreased physical activity, it is reasonable to suspect that in older, frail, or hospitalized patients the loss of muscle mass may actually be much greater than 1% per year. Lack of mechanical stimulation (which is typical of bedrest), immobilization, and sedentary behavior results in thinner and softer articulated cartilage (Reidy et al., 2017). Studies have shown, however, that exercise has the opposite effect. The musculoskeletal system goes through many changes with age. The structure and function of many elements of the system change, although late life exercise can make musculoskeletal system symptoms less severe, serious, and/or painful. All body tissues, including those of the musculoskeletal system, undergo DNA methylation alterations across the life span, which have been shown to reverse after resistance and endurance exercise participation for a period of time (Murach et al., 2022).
regulate bone formation and resorption. Bone is composed of three distinct types of cells. Ninety percent of all bone cells are osteocytes—long-lived bone cells that participate in almost all major bone regulation activities (Atkins & Findlay, 2012). Osteocytes act as regulators of bone formation by detecting strain in the bone. To increase bone formation, the osteocytes transmit signals to osteoblasts, which are the cells responsible for laying down the mineral matrix. Osteoblasts account for 4% to 6% of all bone cells (Atkins & Findlay, 2012). Layers of osteoblasts deposit successive layers of new bony matrix. As these layers are mineralized, new bone is formed. Bone density/mass Equally as important as the formation of new bone is the resorption of older bone. Resorption of older or damaged bone allows for constant bone repair to occur, which ensures healthy bone turnover. Bone resorption is also important for the release of calcium stores from the bone in times of need. Calcium is critical for the propagation of nervous signals and for cellular transport. Cells called osteoclasts, working under the direction of osteocytes, are able to destroy the bony matrix, releasing calcium into the body for use by other cells (Schulman et al., 2011). Osteoclasts are large, multinucleated cells found on the surface of the bone; they account for only 1% to 2% of the cells in bone (Atkins & Findlay, 2012). In a younger adult, the resorption of bone by osteoclasts and the formation of new bone by osteoblasts is usually balanced and results in no net change in bone. In older adults, an uncoupling of bone resorption and formation occurs. With aging, osteoclasts typically increase their activity, while osteoblasts decrease their work of forming new bone, which results in a net loss of bone in older adults (Schulman et al., 2011). This imbalance results in decreased bone mass and increased risk for fracture. Osteoporosis While aging is associated with decreased bone mass, inactivity accelerates this decline, and a sedentary lifestyle is a risk factor for the development of osteoporosis (Booth et al., 2011). Studies have shown that older adults who have been active throughout their lives and have higher cardiovascular fitness also have higher bone density than inactive adults, thus decreasing their risk for osteoporosis (Booth et al., 2011; DeFina et al., 2016). Increased levels of proinflammatory cytokines, which are often associated with physical inactivity, stimulate osteoclasts and result in increased levels of bone resorption. Increased levels of adiposity, which are frequently attributed to a sedentary lifestyle, are also associated with low total bone mineral density. A study of more than 13,000 older adults demonstrated that the percentage of body fat was positively associated with osteopenia, indicating that older adults with increased body fat were more likely to have bone loss (Cao, 2011). While the exact mechanism behind the association between increased fat mass and bone loss is unknown, it is suspected that increased levels of inflammatory cytokines may be the reason this occurs (Cao, 2011). It is known, Summary of body system changes with aging With aging, numerous changes take place throughout the body’s system, and a summary of the changes resulting from aging and inactivity can be found in Table 4. It is clear that activity and exercise slow or even mitigate many age-related
changes, resulting in a delayed onset of frailty and mobility limitations in older adults. The benefits of both aerobic and resistive exercise are numerous and will be explored in greater detail in the following sections.
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