Proctor D N, Joyner M J
Department of Anesthesiology, Mayo Clinic, Rochester, Minnesota 55905, USA.
J Appl Physiol (1985). 1997 May;82(5):1411-5. doi: 10.1152/jappl.1997.82.5.1411.
The role of skeletal muscle mass in the age-associated decline in maximal O2 uptake (VO2max) is poorly defined because of confounding changes in muscle oxidative capacity and in body fat and the difficulty of quantifying active muscle mass during exercise. We attempted to clarify these issues by examining the relationship between several indexes of muscle mass, as estimated by using dual-energy X-ray absorptiometry and treadmill VO2max in 32 chronically endurance-trained subjects from four groups (n = 8/group): young men (20-30 yr), older men (56-72 yr), young women (19-31 yr), and older women (51-72 yr). VO2max per kilogram body mass was 26 and 22% lower in the older men (45.9 vs. 62.0 ml.kg-1.min-1) and older women (40.0 vs. 51.5 ml.kg-1.min-1). These age differences were reduced to 14 and 13%, respectively, when VO2max was expressed per kilogram of appendicular muscle. When appropriately adjusted for age and gender differences in appendicular muscle mass by analysis of covariance, whole body VO2max was 0.50 +/- 0.09 l/min less (P < 0.001) in the older subjects. This effect was similar in both genders. These findings suggest that the reduced VO2max seen in highly trained older men and women relative to their younger counterparts is due, in part, to a reduced aerobic capacity per kilogram of active muscle independent of age-associated changes in body composition, i.e., replacement of muscle tissue by fat. Because skeletal muscle adaptations to endurance training can be well maintained in older subjects, the reduced aerobic capacity per kilogram of muscle likely results from age-associated reductions in maximal O2 delivery (cardiac output and/or muscle blood flow).
由于肌肉氧化能力、体脂的混杂变化以及运动期间量化活跃肌肉量的困难，骨骼肌质量在与年龄相关的最大摄氧量（VO₂max）下降中的作用尚不清楚。我们试图通过研究32名来自四组（每组n = 8）长期耐力训练受试者的肌肉质量的几个指标之间的关系来阐明这些问题，这四组分别是：年轻男性（20 - 30岁）、老年男性（56 - 72岁）、年轻女性（19 - 31岁）和老年女性（51 - 72岁），肌肉质量指标通过双能X线吸收法估算，同时测量跑步机上的VO₂max。老年男性（45.9对62.0 ml·kg⁻¹·min⁻¹）和老年女性（40.0对51.5 ml·kg⁻¹·min⁻¹）每千克体重的VO₂max分别降低了26%和22%。当以每千克附属肌肉表示VO₂max时，这些年龄差异分别降至14%和13%。通过协方差分析对附属肌肉质量的年龄和性别差异进行适当调整后，老年受试者的全身VO₂max少0.50±0.09 l/min（P < 0.001）。这种效应在两性中相似。这些发现表明，相对于年轻同龄人，训练有素的老年男性和女性中VO₂max降低，部分原因是每千克活跃肌肉的有氧能力降低，这与年龄相关的身体成分变化（即肌肉组织被脂肪替代）无关。由于老年受试者对耐力训练的骨骼肌适应性可以得到很好的维持，每千克肌肉有氧能力的降低可能是由于与年龄相关的最大氧输送（心输出量和/或肌肉血流量）减少所致。
