Power fatigue of the rat diaphragm muscle
Power fatigue of the rat diaphragm muscle
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DOI：
10.1152/jappl.2000.89.6.2215
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发表时间：
2000-12-01
影响因子：
3.3
通讯作者：
Sieck, GC
中科院分区：
文献类型：
--
作者：
Ameredes, BT;Zhan, WZ;Sieck, GC
我们假设，重复激活的大鼠隔膜(Dia)肌的最大功率输出((W)/点(Max))的减少是由于与缩短速度(速度疲劳)的减慢相比，力(力疲劳)的不成比例减少。在体外(26℃)固定肋中肌，以每秒重复400ms(占空比=0.4)的训练序列，以75 Hz的频率直接刺激120名S，用一种新的技术来监测疲劳过程中最大比力(P-o)和W-max的瞬时减少。在每个刺激序列中，在最初的360毫秒内，激活是等长的，在此期间测量P-O；然后允许肌肉在最后40毫秒内以恒定速度(30%V-max)缩短，并确定(W)对点(Max)。与初始值相比，重复激活120次S后，P-o和(W)Over Dot(Max)分别下降了75%和73%。最大缩短速度的测量有两种方法：外推力-速度关系(V-max)和松弛试验[最大无负荷缩短速度(V-O)]。重复激活120次S后，V-max减慢44%，而V-O减慢22%。因此，重复激活后W的降低主要是力疲劳，速度疲劳起次要作用。在V-max比V-O减慢的基础上，我们还得出结论，力和功率疲劳不能简单地归因于最易疲劳的纤维类型的完全失活。
We hypothesized that decrements in maximum power output ((W)over dot(max)) of the rat diaphragm (Dia) muscle with repetitive activation are due to a disproportionate reduction in force (force fatigue) compared with a slowing of shortening velocity (velocity fatigue). Segments of midcostal Dia muscle were mounted in vitro (26 degreesC) and stimulated directly at 75 Hz in 400-ms-duration trains repeated each second (duty cycle = 0.4) for 120 s. A novel technique was used to monitor instantaneous reductions in maximum specific force (P-o) and W-max during fatigue. During each stimulus train, activation was isometric for the initial 360 ms during which P-o was measured; the muscle was then allowed to shorten at a constant velocity (30% V-max) for the final 40 ms, and (W)over dot(max) was determined. Compared with initial values, after 120 s of repetitive activation, P-o and (W)over dot(max) decreased by 75 and 73%, respectively. Maximum shortening velocity was measured in two ways: by extrapolation of the force-velocity relationship (V-max) and using the slack test [maximum unloaded shortening velocity (V-o)]. After 120 s of repetitive activation, V-max slowed by 44%, whereas V-o slowed by 22%. Thus the decrease in W with repetitive activation was dominated by force fatigue, with velocity fatigue playing a secondary role. On the basis of a greater slowing of V-max vs. V-o, we also conclude that force and power fatigue cannot be attributed simply to the total inactivation of the most fatigable fiber types.