Krustrup Peter, Secher Niels H, Relu Mihai U, Hellsten Ylva, Söderlund Karin, Bangsbo Jens
Department of Exercise and Sport Sciences, Section of Human Physiology, The August Krogh Building, Universitetsparken 13, DK-2100 Copenhagen Ø, Denmark.
J Physiol. 2008 Dec 15;586(24):6037-48. doi: 10.1113/jphysiol.2008.158162. Epub 2008 Oct 27.
We tested the hypothesis that a greater activation of fast-twitch (FT) fibres during dynamic exercise leads to a higher muscle oxygen uptake (VO2 ) and energy turnover as well as a slower muscle on-kinetics. Subjects performed one-legged knee-extensor exercise for 10 min at an intensity of 30 W without (CON) and with (CUR) arterial injections of the non-depolarizing neuromuscular blocking agent cisatracurium. In CUR, creatine phosphate (CP) was unaltered in slow twitch (ST) fibres and decreased (P < 0.05) by 28% in FT fibres, whereas in CON, CP decreased (P < 0.05) by 33% and 23% in ST and FT fibres, respectively. From 127 s of exercise, muscle VO2 was higher (P < 0.05) in CUR compared to CON (425 +/- 25 (+/- S.E.M.) versus 332 +/- 30 ml min(-1)) and remained higher (P < 0.05) throughout exercise. Using monoexponential fitting, the time constant of the exercise-induced muscle VO2 response was slower (P < 0.05) in CUR than in CON (55 +/- 6 versus 33 +/- 5 s). During CUR and CON, muscle homogenate CP was lowered (P < 0.05) by 32 and 35%, respectively, and also muscle lactate production was similar in CUR and CON (37.8 +/- 4.1 versus 35.2 +/- 6.2 mmol). Estimated total muscle ATP turnover was 19% higher (P < 0.05) in CUR than in CON (1196 +/- 90 versus 1011 +/- 59 mmol) and true mechanical efficiency was lower (P < 0.05) in CUR than in CON (26.2 +/- 2.0 versus 30.9 +/- 1.5%). In conclusion, the present findings provide evidence that FT fibres are less efficient than ST fibres in vivo at a contraction frequency of 1 Hz, and that the muscle VO2 kinetics is slowed by FT fibre activation.
动态运动期间快肌（FT）纤维的更大激活会导致更高的肌肉摄氧量（VO₂）和能量转换，以及更慢的肌肉启动动力学。受试者在30W强度下进行单腿伸膝运动10分钟，分别在不进行（CON）和进行（CUR）非去极化神经肌肉阻滞剂顺式阿曲库铵动脉注射的情况下进行。在CUR组中，慢肌（ST）纤维中的磷酸肌酸（CP）未改变，而FT纤维中的CP降低（P<0.05）了28%；而在CON组中，ST和FT纤维中的CP分别降低（P<0.05）了33%和23%。从运动127秒起，CUR组的肌肉VO₂高于CON组（P<0.05）（425±25（±标准误）对332±30ml·min⁻¹），且在整个运动过程中一直较高（P<0.05）。使用单指数拟合，CUR组运动诱导的肌肉VO₂反应的时间常数比CON组慢（P<0.05）（55±6对33±5秒）。在CUR组和CON组期间，肌肉匀浆CP分别降低（P<0.05）了32%和35%，且CUR组和CON组的肌肉乳酸生成量相似（37.8±4.1对35.2±6.2mmol）。估计的总肌肉ATP转换率CUR组比CON组高19%（P<0.05）（1196±90对1011±59mmol），且CUR组的真实机械效率低于CON组（P<0.05）（26.2±2.0对30.9±1.5%）。总之，目前的研究结果表明，在1Hz的收缩频率下，FT纤维在体内的效率低于ST纤维，并且FT纤维的激活会减慢肌肉VO₂动力学。
