Department of Sport and Exercise Science, Aberystwyth University, Ceredigion, UK.
Exp Physiol. 2010 Jul;95(7):798-807. doi: 10.1113/expphysiol.2010.052688. Epub 2010 Apr 1.
It is not possible to attain a metabolic steady state during exercise above the so-called critical force or critical power. We tested the hypothesis that the muscle metabolic perturbations at the end of a bout of maximal isometric contractions, which yield a stable end-test force (equal to the critical force), would be similar to that at task failure following submaximal contractions performed above the critical force. Eight healthy subjects (four female) performed isometric single knee-extension exercise in the bore of a 1.5 T superconducting magnet on two occasions. Following familiarization, subjects performed the following exercises: (1) 60 maximal contractions (3 s contraction, 2 s rest); and (2) submaximal contractions (the same contraction regime performed at 54 +/- 8% maximal voluntary contraction) to task failure. Phosphocreatine (PCr), inorganic phosphate (P(i)) and diprotonated phosphate (H(2)PO(4)()) concentrations and pH were determined using (31)P magnetic resonance spectroscopy throughout both tests. During the maximal contractions, force production fell from 213 +/- 33 N to reach a plateau in the last 30 s of the test at 100 +/- 20 N. The muscle metabolic responses at the end of each test were substantial, but not different between conditions: [PCr] was reduced (to 21 +/- 12 and 17 +/- 7% of baseline for maximal and submaximal contractions, respectively; P = 0.17), [P(i)] was elevated (to 364 +/- 98 and 363 +/- 135% of baseline, respectively; P = 0.98) and pH reduced (to 6.64 +/- 0.16 and 6.69 +/- 0.17, respectively; P = 0.43). The [H(2)PO(4)()] was also elevated at the end of both tests (to 607 +/- 252 and 556 +/- 269% of baseline, respectively; P = 0.22). These data suggest that the exercise-induced metabolic perturbations contributing to force depression in all-out exercise are the same as those contributing to task failure during submaximal contractions.
在所谓的临界力或临界功率以上进行运动时，无法达到代谢稳态。我们检验了这样一个假设，即在最大等长收缩结束时，肌肉代谢的波动会产生稳定的末端测试力（等于临界力），这与在临界力以上进行的次最大收缩后任务失败时的代谢波动相似。8 名健康受试者（4 名女性）在 1.5T 超导磁体的腔体内进行了两次单膝伸展等长收缩运动。在熟悉之后，受试者进行了以下练习：（1）60 次最大收缩（3 秒收缩，2 秒休息）；（2）次最大收缩（以 54%±8%最大自主收缩的相同收缩模式）至任务失败。在两次测试中，均使用（31）P 磁共振波谱法测定磷酸肌酸（PCr）、无机磷（P（i））和二质子化磷酸盐（H（2）PO（4）（））浓度和 pH 值。在最大收缩期间，力的产生从 213±33N 下降，在测试的最后 30s 达到平台，为 100±20N。在每次测试结束时，肌肉代谢反应都很显著，但在两种情况下没有差异：[PCr]降低（最大收缩和次最大收缩分别为基础值的 21%±12%和 17%±7%；P=0.17），[P（i）]升高（分别为基础值的 364%±98%和 363%±135%；P=0.98），pH 值降低（分别为 6.64±0.16 和 6.69±0.17，P=0.43）。在两次测试结束时，[H（2）PO（4）]（）也升高（分别为基础值的 607%±252%和 556%±269%，P=0.22）。这些数据表明，导致全力运动中力下降的运动引起的代谢波动与次最大收缩后任务失败时的代谢波动相同。
