Vedsted P, Larsen A H, Madsen K, Sjøgaard G
Department of Physiology, National Institute of Occupational Health, Lersø Parkallé 105, DK 2100 Copenhagen Ø, Denmark.
Acta Physiol Scand. 2003 Jun;178(2):175-86. doi: 10.1046/j.1365-201X.2003.01123.x.
To study the effect of contraction mode on fatigue development.
Muscle fatigue was induced by isotonic and quasi-isometric contractions in rat soleus (SOL) and extensor digitorum longus (EDL) muscles, using identical stimulation protocol (60 Hz, 400 ms s-1) for 100 s in SOL and 60 s in EDL. Fatigue was quantified as the decline in peak values of shortening, shortening velocity, relaxation and work during the isotonic contractions, and, correspondingly, of force, rate of force development, relaxation and work during the quasi-isometric contractions. Maximal test contractions (60 Hz, 1.5 s) performed before and after fatigue were analysed for decline in force development (Fmax), rate of force development (dF/dtmax) and relaxation (-dF/dtmax).
Fmax declined to significantly lower values after isotonic than after quasi-isometric fatiguing contractions (fatigued in percentage of unfatigued): 58.5 +/- 6.4% vs. 64.4 +/- 7.0% in SOL, and 30.4 +/- 4.1% vs. 33.3 +/- 3.6% in EDL, respectively. The same pattern was seen for dF/dtmax which decreased to: 46.3 +/- 9.9% vs. 52.3 +/- 8.5% in SOL, and 19.1 +/- 4.3% vs. 22.3 +/- 3.2% in EDL after isotonic and quasi-isometric contractions, respectively. Similarly, when comparing fatigue development during the two contraction modes, the respective fatigue variables decreased more rapidly and to lower levels during isotonic vs. quasi-isometric contractions. During maximal test contractions, the dynamic fatigue variables (+/-dF/dtmax) declined to significantly lower levels than Fmax.
Fatigue development was significantly larger during isotonic vs. quasi-isometric contractions. The use of force as the only experimental fatigue variable may underestimate the functional impairment of fatigued muscle, neglecting the fatigue effect on time and length dimensions.
研究收缩模式对疲劳发展的影响。
通过等张收缩和准等长收缩诱导大鼠比目鱼肌（SOL）和趾长伸肌（EDL）产生肌肉疲劳，对SOL采用相同的刺激方案（60Hz，400ms s-1）持续100s，对EDL持续60s。疲劳程度通过等张收缩过程中缩短峰值、缩短速度、舒张和做功的下降来量化，相应地，通过准等长收缩过程中的力、力发展速率、舒张和做功的下降来量化。分析疲劳前后进行的最大测试收缩（60Hz，1.5s）的力发展（Fmax）、力发展速率（dF/dtmax）和舒张（-dF/dtmax）的下降情况。
等张疲劳收缩后Fmax下降到显著低于准等长疲劳收缩后的水平（疲劳相对于未疲劳的百分比）：SOL中分别为58.5±6.4%和64.4±7.0%，EDL中分别为30.4±4.1%和33.3±3.6%。dF/dtmax也呈现相同模式，等张收缩和准等长收缩后，SOL中分别下降到46.3±9.9%和52.3±8.5%，EDL中分别下降到19.1±4.3%和22.3±3.2%。同样，比较两种收缩模式下的疲劳发展时，等张收缩过程中各个疲劳变量下降得更快且达到更低水平。在最大测试收缩过程中动态疲劳变量（±dF/dtmax）下降到显著低于Fmax的水平。
等张收缩过程中的疲劳发展显著大于准等长收缩。仅将力作为实验疲劳变量可能会低估疲劳肌肉的功能损害，而忽略了疲劳对时间和长度维度的影响。
