The projects focus is on describing the characteristic losses in muscle strength, muscle mass, and physical functioning that occur with aging by examining the entire adult lifespan and the impact on function and longevity. We previously demonstrated that declining muscle strength and rate of change of muscle strength are independent contributors to mortality in men when considering age, physical activity and muscle mass. Further, strength is directly related to walking speed a risk for functional disability in the elderly. We have further shown that muscle power and movement speed are further independent sarcopenic factors that contribute to longevity. In the past year, we participated in an international collaborative study which conducted a quantitative systematic review and meta-analysis, examining the associations between physical capability (grip strength, walking speed, chair rising and standing balance times) and mortality in community-dwelling populations. Evidence was found for associations between poorer performance on physical capability and increased mortality. Muscle strength and the use of that strength for physical functioning are important contributors to health and longevity.. A key contributor for the maintenance and utilization of the muscle is the nervous system. Previously, we have shown that peripheral nerve function has an impact on muscle strength and power independent of body size and activity levels. Further observations suggest that force generation requires greater nervous system activity to obtain a given force level as we age as an adjustment for the decrease in strength, decline in movement speed and response times. Alterations in both the peripheral and central nervous systems seem to be major contributors to the sarcopenic process. In related work, we found that declines in vibrotactile sensitivity in the feet with age, and that vibrotactile sensitivity is directly related to physical performance with slower self-selected normal gait speed. Thus both sensory and motor components of the peripheral nervous system seem associated with a decline in mobility which subsequently contributes to loss of leg strength and corresponding muscle changes that are major components of sarcopenia. Based on these observations, we developed a Cumulative Somatosensory Impairment Index (CSII) that detects group differences in lower limb somatosensory impairment and is an independent predictor of decline in postural control over 3 years. Such an index may prove useful in assessing future physical functioning problems. When considering sensorimotor and psychosocial factors in relationship to adaptive walking tasks in older adults, we found that poor knee extensor strength was associated with an inability to perform tasks demanding an increase in walking speed (fast walking and obstacle crossing). Both poor lower limb coordination and higher CSII were significantly associated with failure in tests that demanded precise control over foot placement (obstacle crossing and narrow-based walking). In contrast, poor cognition was associated with an inability to perform walking while talking. Poor personal mastery was the only variable that was associated with failure in all walking tests. The impact of sarcopenia on mortality may in part be dependent on homeostatic factors required in neuromuscular function maintenance. We previously observed that basal metabolic rate declined with age at a rate that accelerated at older ages. Participants who died had a higher basal metabolic rates compared to those who survived independent of other well-recognized risk factors for mortality. Further, we have observed that increasing glucose intolerance is associated with increasing mortality independent of the development of diabetes. Recently, we have extended this work to study the relationship of glucose intolerance with changes in muscle mass with aging. Associated with the metabolic changes, we have recently shown that weight loss, which is frequently seen prior to death, often begins 9 or more years before death. This effect is likely related to differences in dietary intake, and energy metabolism during these years prior to death. Age related declines in testosterone in men may contribute to losses in muscle strength and physical performance. We previously reported that free testosterone in adult men was modestly but directly related to arm and leg strength independent of fat free mass and age, and indirectly related through body mass. We recently evaluated the question focusing on older men from the InCHIANTI study. With increased severity of hypogonadal status, participants were significantly older with substantially similar body mass indexes and showed differences in hemoglobin levels, hand grip strength and a physical performance score but not for calf muscle mass and 4 meter walking speed. These studies demonstrate that in both younger and older men, gonadal status is independently associated with some determinants of physical performance. Another area of interest has been the importance of physical activity and exercise on strength and muscle mass. We have observed that both being physically active and maintaining higher intensity activity over time is associated with lower mortality in men, but not women. In women, overall activity, including low and moderate levels, are equally important. Thus, different strategies and activities might be important based on sex. In addition, in the elderly, activity restriction can occur because of fear of falling. We observed that such fears adversely affect physical function and autonomy in the In Chianti population. Thus both psychological and physical factors appear to contribute to fear of falling and the associated restrictions in physical activity. Furthermore, differences in physical and psychosocial characteristics exist between older persons who have fear of falling in community environment activities and those who express fear of falling in home environment activities. Personality, a significant determinant of health behaviors including physical activity, could therefore impact muscle strength throughout adulthood and affect the rate of muscle strength decline with aging. Personality typologies combining high neuroticism (N≥55), low extraversion (E<45), and low conscientiousness (C<45) have been associated with multiple risky health behaviors which raise the question whether there is an association between individual and combined typologies consisting of high N, low E, and low C and muscle strength. Using Baltimore Longitudinal Study of Aging data, high N, particularly when combined with either low E or low C, were associated with lower muscle strength compared with having only one or none of these personality types. Physical activity level appears to partly explain some of the associations. Some aspects of personality appear to be contribute to age associated strength loss, and may need to be considered in developing approaches to overcome these losses. These differences suggest the importance of exploring the environment where the fear occurs. Activity interventions need to consider such issues in designing appropriate physical activities and exercise interventions. We have been interested in alternative strategies for exercise intervention for those less inclined to directly exercise including electromyostimulation and a pedometer as a motivational tool to increase activity. Work in this project will continue to explore important physiological, social and activity related factors contributing to strength loss and performance declines with aging. The long term goal is to develop strategies that can be used across the adult lifespan to maintain and improve physical performance. These strategies are likely to differ at different ages, and for women and men.
Showing the most recent 10 out of 35 publications
