Nutrition, Exercise Physiology and Sarcopenia Laboratory, Jean Mayer United States Department of Agriculture Human Nutrition Research Center on Aging at Tufts University, 711 Washington Street, Boston, MA 02111, USA.
Eur J Appl Physiol. 2012 Jun;112(6):2289-301. doi: 10.1007/s00421-011-2200-0. Epub 2011 Oct 18.
This study investigated the physiological and gender determinants of the age-related loss of muscle power in 31 healthy middle-aged adults (aged 40-55 years), 28 healthy older adults (70-85 years) and 34 mobility-limited older adults (70-85 years). We hypothesized that leg extensor muscle power would be significantly lower in mobility-limited elders relative to both healthy groups and sought to characterize the physiological mechanisms associated with the reduction of muscle power with aging. Computed tomography was utilized to assess mid-thigh body composition and calculate specific muscle power and strength. Surface electromyography was used to assess rate of neuromuscular activation and muscle biopsies were taken to evaluate single muscle fiber contractile properties. Peak muscle power, strength, muscle cross-sectional area, specific muscle power and rate of neuromuscular activation were significantly lower among mobility-limited elders compared to both healthy groups (P ≤ 0.05). Mobility-limited older participants had greater deposits of intermuscular adipose tissue (P < 0.001). Single fiber contractile properties of type I and type IIA muscle fibers were preserved in mobility-limited elders relative to both healthy groups. Male gender was associated with greater decrements in peak and specific muscle power among mobility-limited participants. Impairments in the rate of neuromuscular activation and concomitant reductions in muscle quality are important physiological mechanisms contributing to muscle power deficits and mobility limitations. The dissociation between age-related changes at the whole muscle and single fiber level suggest that, even among older adults with overt mobility problems, contractile properties of surviving muscle fibers are preserved in an attempt to maintain overall muscle function.
本研究调查了 31 名健康中年成年人（40-55 岁）、28 名健康老年人（70-85 岁）和 34 名行动受限老年人（70-85 岁）中与年龄相关的肌肉力量丧失的生理和性别决定因素。我们假设行动受限的老年人的腿部伸肌力量明显低于健康组，并试图描述与肌肉力量随年龄下降相关的生理机制。使用计算机断层扫描评估大腿中段身体成分并计算特定肌肉力量和强度。表面肌电图用于评估神经肌肉激活率，肌肉活检用于评估单根肌肉纤维的收缩特性。与健康组相比，行动受限的老年人的峰值肌肉力量、强度、肌肉横截面积、特定肌肉力量和神经肌肉激活率均显著降低（P≤0.05）。行动受限的老年人有更多的肌间脂肪组织沉积（P<0.001）。与健康组相比，行动受限的老年人的 I 型和 IIA 型肌肉纤维的单纤维收缩特性得到了保留。男性性别与行动受限参与者的峰值和特定肌肉力量的更大下降有关。神经肌肉激活率的受损以及随之而来的肌肉质量的降低是导致肌肉力量下降和行动受限的重要生理机制。在整个肌肉和单纤维水平上与年龄相关的变化之间的分离表明，即使在有明显行动问题的老年人中，存活肌肉纤维的收缩特性也得到了保留，以试图维持整体肌肉功能。
