Chung Linda H, Callahan Damien M, Kent-Braun Jane A
Dept. of Kinesiology, Univ. of Massachusetts, 108 Totman Bldg., 30 Eastman Lane, Amherst, MA 01003, USA.
J Appl Physiol (1985). 2007 Nov;103(5):1628-35. doi: 10.1152/japplphysiol.00320.2007. Epub 2007 Aug 9.
During voluntary contractions, the skeletal muscle of healthy older adults often fatigues less than that of young adults, a result that has been explained by relatively greater reliance on muscle oxidative metabolism in the elderly. Our aim was to investigate whether this age-related fatigue resistance was eliminated when oxidative metabolism was minimized via ischemia induced by cuff (220 mmHg). We hypothesized that 1) older men (n = 12) would fatigue less than young men (n = 12) during free-flow (FF) contractions; 2) both groups would fatigue similarly during ischemia; and 3) reperfusion would reestablish the fatigue resistance of the old. Subjects performed 6 min of intermittent, maximal voluntary isometric contractions of the ankle dorsiflexors under FF and ischemia-reperfusion (IR) conditions. Ischemia was maintained for the first 3 min of contractions, followed by rapid cuff deflation and reperfusion for 3 additional minutes of contractions. Central activation, peripheral activation, and muscle contractile properties were measured at 3 and 6 min of contractions. Older men fatigued less than young men during FF (P </= 0.02), ischemia (P < 0.001), and reperfusion (P < 0.001). During FF, activation and contractile properties changed similarly across age groups. At the end of ischemia, central (P = 0.02) and peripheral (P </= 0.03) activation declined more in the young, with no effect of age on the changes in contractile properties. Thus age-related fatigue resistance was evident during FF and IR, indicating that differences in blood flow and oxidative metabolism do not explain the fatigue resistance of old age.
在自主收缩过程中，健康老年人的骨骼肌往往比年轻人更不容易疲劳，这一结果被解释为老年人相对更依赖肌肉氧化代谢。我们的目的是研究当通过袖带（220 mmHg）诱导的缺血使氧化代谢降至最低时，这种与年龄相关的抗疲劳能力是否会消失。我们假设：1）在自由血流（FF）收缩期间，老年男性（n = 12）比年轻男性（n = 12）疲劳程度更低；2）在缺血期间，两组的疲劳程度相似；3）再灌注将恢复老年人的抗疲劳能力。受试者在FF和缺血再灌注（IR）条件下，对踝背屈肌进行6分钟的间歇性最大自主等长收缩。在收缩的前3分钟维持缺血状态，随后迅速放气袖带并再灌注3分钟以继续收缩。在收缩3分钟和6分钟时测量中枢激活、外周激活和肌肉收缩特性。在FF、缺血和再灌注期间，老年男性的疲劳程度均低于年轻男性（P≤0.02、P<0.001、P<0.001）。在FF期间，各年龄组的激活和收缩特性变化相似。在缺血结束时，年轻人的中枢激活（P = 0.02）和外周激活（P≤0.03）下降幅度更大，年龄对收缩特性的变化没有影响。因此，在FF和IR期间，与年龄相关的抗疲劳能力很明显，这表明血流和氧化代谢的差异并不能解释老年人的抗疲劳能力。
