Payne Anthony M, Dodd Stephen L, Leeuwenburgh Christiaan
Muscle Physiology Laboratory, University of Florida, Center for Exercise Science, Gainesville, FL 32611, USA.
J Appl Physiol (1985). 2003 Dec;95(6):2554-62. doi: 10.1152/japplphysiol.00758.2003. Epub 2003 Sep 12.
The decline in muscle function is associated with an age-related decrease in muscle mass and an age-related decline in strength. However, decreased strength is not solely due to decreased muscle mass. The age-related decline in muscle-specific force (force/muscle cross-sectional area), a measure of intrinsic muscle function, also contributes to age-related strength decline, and the mechanisms by which this occurs are only partially known. Moreover, changes in the extracellular space could have a profound effect on skeletal muscle function. Life-long calorie restriction in rodents has shown to be a powerful anti-aging intervention. In this study, we examine whether calorie restriction is able to attenuate the loss of muscle function and elevations in extracellular space associated with aging. We hypothesize that calorie restriction attenuates the age-associated decline in specific force and increases in extracellular space. Measurements of in vitro contractile properties of the extensor digitorum longus (type II) and soleus (type I) muscles from 12-mo and 26- to 28-mo-old ad libitum-fed, as well as 27- to 28-mo-old life-long calorie-restricted male Fischer 344 rats, were performed. We found that calorie restriction attenuated the age-associated decline in muscle mass-to-body mass ratio (mg/g) and strength-to-body mass ratio (N/kg) in the extensor digitorum longus muscle (P < 0.05) but not in the soleus muscle (P > 0.05). Importantly, muscle-specific force (N/cm2) in the extensor digitorum longus, but not in the soleus muscle, of the old calorie-restricted rats was equal to that of the young 12-mo-old animals. Moreover, the age-associated increase in extracellular space was reduced in the fast-twitch extensor digitorum longus muscle (P < 0.05) but not in the soleus muscle with calorie restriction. We also found a significant correlation between the extracellular space and the muscle-specific force in the extensor digitorum longus (r = -0.58; P < 0.05) but not in the soleus muscle (r = -0.38; P > 0.05). Hence, this study shows a loss of muscle function with age and suggests that long-term calorie restriction is an effective intervention against the loss of muscle function with age.
肌肉功能的衰退与肌肉质量随年龄增长而下降以及力量随年龄增长而衰退有关。然而，力量下降并非仅仅是由于肌肉质量减少。肌肉比力（力/肌肉横截面积）这一衡量肌肉内在功能的指标随年龄增长而下降，这也导致了与年龄相关的力量衰退，而其发生机制仅部分为人所知。此外，细胞外空间的变化可能对骨骼肌功能产生深远影响。啮齿动物终生热量限制已被证明是一种有效的抗衰老干预措施。在本研究中，我们探究热量限制是否能够减轻与衰老相关的肌肉功能丧失以及细胞外空间的增加。我们假设热量限制可减轻与年龄相关的比力下降并减少细胞外空间的增加。对12月龄和26至28月龄自由进食的雄性Fischer 344大鼠以及27至28月龄终生热量限制的雄性Fischer 344大鼠的趾长伸肌（II型）和比目鱼肌（I型）的体外收缩特性进行了测量。我们发现，热量限制减轻了趾长伸肌中与年龄相关的肌肉质量与体重比（mg/g）和力量与体重比（N/kg）的下降（P < 0.05），但对比目鱼肌没有影响（P > 0.05）。重要的是，老年热量限制大鼠的趾长伸肌而非比目鱼肌的肌肉比力（N/cm²）与年轻的12月龄动物相当。此外，热量限制使快肌趾长伸肌中与年龄相关的细胞外空间增加减少（P < 0.05），但对比目鱼肌没有影响。我们还发现，趾长伸肌的细胞外空间与肌肉比力之间存在显著相关性（r = -0.58；P < 0.05），而比目鱼肌中不存在这种相关性（r = -0.38；P > 0.05）。因此，本研究表明肌肉功能会随年龄增长而丧失，并提示长期热量限制是对抗肌肉功能随年龄丧失的有效干预措施。
