older adult’s heart is unable to keep pace with a young adult’s heart, and large differences are seen between young and old individuals’ ability to perform vigorous exercise. Maximal cardiac output, or the maximal amount of blood the heart can pump in one minute, decreases with aging by as much as 25%, and maximal oxygen uptake, known as VO 2 max decreases by 50% between the ages of 20 and 80 (Strait & Lakatta, 2012). VO 2 max is a measure of cardiovascular fitness of an individual, and decreased rates indicate lower physical fitness. While even master athletes experience declines in VO 2 max with aging, Respiratory system changes The respiratory system includes the thoracic cage (which encompasses the ribs, thoracic vertebrae, and the intercostal muscles), the lungs, and diaphragm. It is theorized that, as in the cardiovascular system, a lifetime of cellular stress and damage leads to changes in the lung’s tissue as well as in the thoracic cage and diaphragm, resulting in decreased function of the respiratory system with aging. At a cellular level, there are numerous changes in the lung tissue, or parenchyma, including a decrease in the elastic tissue within the lungs that results in a decrease in the elastic recoil of the lungs as well as a premature closure of small airways during normal breathing. This results in air trapping and an inability to completely empty the lungs (Sharma & Goodwin, 2006). At the same time, cellular changes in the thoracic cage result in an increased stiffness of the intercostal muscles and calcification of the costal cartilages, resulting in decreased ability of the lungs to expand. Osteoporosis and a lifetime of poor posture may also contribute to the development or worsening of kyphotic posture due to reduced height of the thoracic vertebrae and a collapse of the thoracic intervertebral discs (Chester & Rudolph, 2011). As a result of the structural changes in the thoracic cage and an increase in kyphotic posture, there is a loss of chest wall compliance, or the ability of Endocrine system changes The endocrine system is responsible for regulating the body’s metabolism through the release of hormones that act as signals to cells throughout the body. These chemical messengers act to coordinate a whole body response among various systems. For example, the release of the hormone insulin from the pancreas results in an increased uptake of glucose in most cells of the body. Aging is associated with numerous changes in the release and regulation of multiple hormones that result in changes in whole body fat mass, increased inflammation, and an increased risk for metabolic diseases such as diabetes. Total body fat mass typically increases until the age of 65 and then either decreases or remains unchanged (Barzilai et al., 2012). While whole body fat mass may remain stable or even decrease with aging, the distribution of this fat mass changes dramatically. As an individual ages, fat is no longer stored in the subcutaneous fat depot beneath the skin, but is instead stored in other more harmful locations, such as in and around the abdominal organs and underneath the muscle fascia in and between muscle fibers. These alternate locations of fat storage, also known as ectopic fat deposits, result in an increased release of proinflammatory cytokines from adipose tissue and an increase in whole body inflammation (Barzilai et al., 2012). Adipose tissue was once thought to be an inert storage depot for excess calories, but the past 10 years have provided increasing evidence that, far from being inert, adipose tissue is in fact the largest endocrine organ in the body (Stehno-Bittel, 2008). Increased amounts of adipose tissue release a host of hormones and proinflammatory cytokines that have negative effects on mobility and function in older adults (Marcus, Brixner, Ghate, & LaStayo, 2012; Stehno- Bittel, 2008). However, not all adipose tissue is equally harmful. Adipose tissue stored in the subcutaneous tissue poses less of a health risk than adipose tissue stored in the abdominal cavity, also known as visceral adipose tissue, or within the muscle, known as intramuscular adipose tissue (Addison et al., 2014; Sepe, Tchkonia, Thomou, Zamboni, & Kirkland, 2011; Stehno- Bittel,2008).
inactivity can accelerate the loss, and sedentary individuals may experience decreases in VO 2 max by as much as 10% per decade after the age of 25 (Strait & Lakatta, 2012). The changes in the cardiovascular system are numerous and take place throughout the entire body. While it is clear that we do not fully understand the age-related changes that occur in the cardiovascular system, we do know that exercise intervention can delay and even reverse some of these changes (Booth et al., 2011; Booth & Zwetsloot, 2010). the chest to expand with inhalation. The decreased chest wall compliance results in an increased amount of work necessary to bring in a normal volume of air. The increase in kyphotic posture additionally places the diaphragm at a mechanical disadvantage and reduces its efficiency of contraction (Chester & Rudolph, 2011), which, when combined with the decreased strength of the diaphragm that occurs with aging, results in further decreases in the efficiency of breathing (Sharma & Goodwin, 2006). The combination of a loss of elastic recoil in the lungs with a decrease in chest wall compliance, along with functional changes in the ability of the diaphragm to efficiently contract, results in increased work to breathe and a decrease in the physiologic reserve for the respiratory system. Similar to the cardiovascular system, at rest there may be minimal changes in older adults, as older adults are able to compensate and adapt. One such example of adaptation is seen in the increased respiratory rate that many older adults experience (Chester & Rudolph, 2011). However, with a systemic stressful event, such as surgery or illness, many older adults may be unable to compensate and experience declines in respiratory function (Chester & Rudolph, 2011). It is not currently known why aging leads to shifts away from adipose storage in the subcutaneous tissue toward the more harmful ectopic locations, but this shift may result from a decrease in sex hormones seen in aging. It is common knowledge that after menopause females experience a dramatic decrease in estrogen, and males also experience a decrease in testosterone of 1% to 2% per year after the age of 40 (Apostolopoulou et al., 2012). The decrease in sex hormones with aging has been associated with a shift toward adipose tissue storage in ectopic locations such as the abdomen or within the muscles. Another potential hormonal contributor to the shift in adipose tissue is growth hormone. Growth hormone also decreases with aging, and this decrease has been shown to result in a shift toward adipose tissue storage in the abdomen, resulting in further increases in fat storage in ectopic locations (Apostolopoulou et al., 2012). The increase in adipose storage in ectopic locations may be one reason for the increase in systemic inflammation seen with aging. This increase in whole body inflammation seen with aging has also been termed inflamm-aging (Franceschi et al., 2000). Inflamm-aging may contribute to the development of a host of age-related systemic diseases such as diabetes, cardiovascular disease, and dementia (Franceschi et al., 2000). Aging is associated with an increase in numerous proinflammatory cytokines, or chemical messengers, that circulate, acting as hormones throughout the body. Chronic increases in proinflammatory cytokine levels measured in the blood are among the most important physiologic correlates of the frailty syndrome, and increased rates of inflammation are related to both aging and inactivity in older adults (Addison et al., 2011). It is currently unknown if the increase in inflammation seen with aging is a direct result of the aging process or if it is alternatively caused by increased levels of inactivity and comorbid conditions often seen with aging (Addison et al., 2011). What is known is that older adults who have higher rates of chronic inflammation compared to their peers experience a larger loss of lean tissue
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