Fulco C S, Lewis S F, Frykman P N, Boushel R, Smith S, Harman E A, Cymerman A, Pandolf K B
US Army Research Institute of Environmental Medicine, Natick, Massachusetts 01760-5007, USA.
J Appl Physiol (1985). 1996 Nov;81(5):1891-900. doi: 10.1152/jappl.1996.81.5.1891.
Using an exercise device that integrates maximal voluntary static contraction (MVC) of knee extensor muscles with dynamic knee extension, we compared progressive muscle fatigue, i.e., rate of decline in force-generating capacity, in normoxia (758 Torr) and hypobaric hypoxia (464 Torr). Eight healthy men performed exhaustive constant work rate knee extension (21 +/- 3 W, 79 +/- 2 and 87 +/- 2% of 1-leg knee extension O2 peak uptake for normoxia and hypobaria, respectively) from knee angles of 90-150 degrees at a rate of 1 Hz. MVC (90 degrees knee angle) was performed before dynamic exercise and during < or = 5-s pauses every 2 min of dynamic exercise. MVC force was 578 +/- 29 N in normoxia and 569 +/- 29 N in hypobaria before exercise and fell, at exhaustion, to similar levels (265 +/- 10 and 284 +/- 20 N for normoxia and hypobaria, respectively; P > 0.05) that were higher (P < 0.01) than peak force of constant work rate knee extension (98 +/- 10 N, 18 +/- 3% of MVC). Time to exhaustion was 56% shorter for hypobaria than for normoxia (19 +/- 5 vs. 43 +/- 7 min, respectively; P < 0.01), and rate of right leg MVC fall was nearly twofold greater for hypobaria than for normoxia (mean slope = -22.3 vs. -11.9 N/min, respectively; P < 0.05). With increasing duration of dynamic exercise for normoxia and hypobaria, integrated electromyographic activity during MVC fell progressively with MVC force, implying attenuated maximal muscle excitation. Exhaustion, per se, was postulated to related more closely to impaired shortening velocity than to failure of force-generating capacity.
使用一种将膝伸肌的最大自主静态收缩（MVC）与动态膝关节伸展相结合的运动装置，我们比较了常氧（758托）和低压缺氧（464托）条件下的渐进性肌肉疲劳，即力量产生能力的下降速率。八名健康男性以1赫兹的频率从90至150度的膝关节角度进行了力竭性恒定工作速率膝关节伸展（常氧和低压缺氧时分别为21±3瓦，单腿膝关节伸展氧气峰值摄取量的79±2%和87±2%）。在动态运动前以及动态运动每2分钟的≤5秒暂停期间进行MVC（膝关节角度90度）。运动前常氧条件下的MVC力量为578±29牛，低压缺氧条件下为569±29牛，力竭时降至相似水平（常氧和低压缺氧时分别为265±10牛和284±20牛；P>0.05），且高于恒定工作速率膝关节伸展的峰值力量（98±10牛，MVC的18±3%；P<0.01）。低压缺氧时的力竭时间比常氧时短56%（分别为19±5分钟和43±7分钟；P<0.01），且低压缺氧时右腿MVC下降速率几乎是常氧时的两倍（平均斜率分别为-22.3牛/分钟和-11.9牛/分钟；P<0.05）。随着常氧和低压缺氧条件下动态运动持续时间的增加，MVC期间的积分肌电图活动随MVC力量逐渐下降，这意味着最大肌肉兴奋性减弱。推测力竭本身与缩短速度受损的关系比与力量产生能力衰竭的关系更密切。
