ABSTRACT
Of the physiological changes associated with advancing age, those occurring in the cardiovascular (CV) system are among the most clinically and functionally relevant. Aging is associated with mild left ventricular hypertrophy, narrowing of the outflow tract from the left ventricle, reduced responsiveness to b-adrenergic stimuli, significant reduction in peak cardiac output, and impaired distensibility of arteries (Ferrari et al., 2003). In addition, aging results in diminished mitochondrial content and capacity in skeletal muscle (Conley et al., 2007). These changes dramatically limit the functional capacity of the CV system at advanced age, such that by age 75 years, over half of the maximal oxygen consumption (VO2max) has been lost (Barnard et al., 1979). Older adults commonly demonstrate VO2max values that are lower than required for many common activities of daily living (Durstine & Moore, 2003). VO2max represents the functional limit of the body’s ability to deliver and extract oxygen to meet the metabolic demands of vigorous physical activity, and is recognized as the international reference standard for physical fitness (Shephard et al., 1968). As well as presenting challenges to physical independence and quality of life, low cardiorespiratory fitness has been consistently associated with CV disease and all-cause mortality (Blair et al., 1996; Myers et al., 2002; Paffenbarger et al., 1978). More importantly, these studies have demonstrated low cardio-respiratory fitness to be a strong and independent predictor of mortality risk (Paffenbarger et al., 1978; Wei et al., 1999).
