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      Age-Related Change in Mobility: Perspectives From Life Course Epidemiology and Geroscience

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          Abstract

          Mobility is the most studied and most relevant physical ability affecting quality of life with strong prognostic value for disability and survival. Natural selection has built the "engine" of mobility with great robustness, redundancy, and functional reserve. Efficient patterns of mobility can be acquired during development even by children affected by severe impairments. Analogously, age-associated impairments in mobility-related physiological systems are compensated and overt limitations of mobility only occur when the severity can no longer be compensated. Mobility loss in older persons usually results from multiple impairments in the central nervous system, muscles, joints, and energetic and sensory physiological systems. Early preclinical changes in these physiological systems that precede mobility loss have been poorly studied. Peak performance, rate of decline, compensatory behaviors, or subclinical deterioration of physiological resources may cumulatively influence both timing of mobility loss and chances of recovery, but their role as risk factors has not been adequately characterized. Understanding the natural history of these early changes and intervening on them would likely be the most effective strategy to reduce the burden of disability in the population. For example, young women with low bone peak mass could be counseled to start strength resistance exercise to reduce their high risk of developing osteoporosis and fracture later in life. Expanding this approach to other physiological domains requires collecting and interpreting data from life course epidemiological studies, establishing normative measures of mobility, physical function, and physical activity, and connecting them with life course trajectories of the mobility-relevant physiological domains.

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          Most cited references10

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          Skeletal muscle mass and distribution in 468 men and women aged 18-88 yr.

          We employed a whole body magnetic resonance imaging protocol to examine the influence of age, gender, body weight, and height on skeletal muscle (SM) mass and distribution in a large and heterogeneous sample of 468 men and women. Men had significantly (P < 0.001) more SM in comparison to women in both absolute terms (33.0 vs. 21.0 kg) and relative to body mass (38.4 vs. 30.6%). The gender differences were greater in the upper (40%) than lower (33%) body (P < 0.01). We observed a reduction in relative SM mass starting in the third decade; however, a noticeable decrease in absolute SM mass was not observed until the end of the fifth decade. This decrease was primarily attributed to a decrease in lower body SM. Weight and height explained approximately 50% of the variance in SM mass in men and women. Although a linear relationship existed between SM and height, the relationship between SM and body weight was curvilinear because the contribution of SM to weight gain decreased with increasing body weight. These findings indicate that men have more SM than women and that these gender differences are greater in the upper body. Independent of gender, aging is associated with a decrease in SM mass that is explained, in large measure, by a decrease in lower body SM occurring after the fifth decade.
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            Human energy expenditure in affluent societies: an analysis of 574 doubly-labelled water measurements.

            To describe average levels of free-living energy expenditure in people from affluent societies and to determine the influence of body weight, height, age and sex. Analysis of 574 measurements of total energy expenditure (TEE, assessed by the doubly-labelled water method); basal metabolic rate (BMR, directly measured or derived from similar directly measured proxy measures such as during sleep); activity energy expenditure (AEE, derived as TEE-BMR); and physical activity level (PAL, derived as TEE/BMR) from people aged 2-95 years. The dataset was extracted from 1614 published and unpublished measurements in 1156 subjects after exclusion of repeat estimates and subjects in special physiological or behavioural states (eg pregnancy, athletic or military training etc). A separate analysis of data from non-ambulant subjects, and from elite endurance athletes (all excluded from the main dataset) established the limits of human daily energy expenditure at around 1.2 x BMR and 4.5 x BMR. In the main analysis, the validity of PAL as an index of TEE adjusted for BMR was tested and confirmed. Regression equations were then derived to describe TEE, BMR, AEE and PAL in terms of body weight, height, age and sex. As anticipated, TEE, BMR and AEE were all positively related to weight and height, while age was a negative predictor, especially of activity. The influence of weight disappeared when TEE was expressed as PAL, but height and age remained as highly significant predictors. For all three components, females expended 11% less energy on average than males after adjustment for weight, height and age. Average levels of energy expenditure in different age and sex groups are tabulated. There now exists a large and robust database of energy expenditure measurements obtained by the doubly-labelled water method. Analysis of the data from affluent societies shows that, in general, levels of energy expenditure are similar to the recommendations for energy requirements adopted by FAO/WHO/UNU (1985) and UK Department of Health (1991). PAL values for active subjects tend to be higher than is currently assumed. The current analysis provides a substantial body of normal data against which other estimates can be compared.
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              Does the amount of fat mass predict age-related loss of lean mass, muscle strength, and muscle quality in older adults?

              An excessive amount of adipose tissue may contribute to sarcopenia and may be one mechanism underlying accelerated loss of muscle mass and strength with aging. We therefore examined the association of baseline total body fat with changes in leg lean mass, muscle strength, and muscle quality over 7 years of follow-up and whether this link was explained by adipocytokines and insulin resistance. Data were from 2,307 men and women, aged 70-79 years, participating in the Health, Aging, and Body Composition study. Total fat mass was acquired from dual energy X-ray absorptiometry. Leg lean mass was assessed by dual energy X-ray absorptiometry in Years 1, 2, 3, 4, 5, 6, and 8. Knee extension strength was measured by isokinetic dynamometer in Years 1, 2, 4, 6, and 8. Muscle quality was calculated as muscle strength divided by leg lean mass. Every SD greater fat mass was related to 1.3 kg more leg lean mass at baseline in men and 1.5 kg in women (p < .01). Greater fat mass was also associated with a greater decline in leg lean mass in both men and women (0.02 kg/year, p < .01), which was not explained by higher levels of adipocytokines and insulin resistance. Larger fat mass was related to significantly greater muscle strength but significantly lower muscle quality at baseline (p < .01). No significant differences in decline of muscle strength and quality were found. High fatness was associated with lower muscle quality, and it predicts accelerated loss of lean mass. Prevention of greater fatness in old age may decrease the loss of lean mass and maintain muscle quality and thereby reducing disability and mobility impairments.
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                Author and article information

                Journal
                The Journals of Gerontology Series A: Biological Sciences and Medical Sciences
                GERONA
                Oxford University Press (OUP)
                1079-5006
                1758-535X
                August 09 2016
                September 2016
                September 2016
                March 14 2016
                : 71
                : 9
                : 1184-1194
                Article
                10.1093/gerona/glw043
                4978365
                26975983
                93e2ac20-af6f-406c-92e4-9a2891929dde
                © 2016
                History

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