Department of Physical Education, National Taiwan Normal University, Taipei City, Taiwan.
School of Medical and Health Sciences, Centre for Exercise and Sports Science Research, Edith Cowan University, Joondalup, WA, Australia.
Scand J Med Sci Sports. 2021 Apr;31(4):813-825. doi: 10.1111/sms.13911. Epub 2021 Jan 7.
The present study tested the hypothesis that 30 low-intensity (10%) eccentric contractions (10%EC) or two maximal voluntary isometric contractions at a long muscle length (2MVIC) that were performed at two days before maximal eccentric exercise of the elbow flexors consisting of five sets of six maximal eccentric contractions (MaxEC) would reduce increases in biceps brachii distal myotendinous junction displacement (MTJd) over the eccentric contractions during MaxEC. Sedentary young men were randomly placed (n = 12/group) to a control group that performed two bouts of MaxEC (CONT-1st, CONT-2nd) separated by two weeks, or one of two preconditioning groups that performed 10%EC or 2MVIC at 20° elbow flexion at two days prior to MaxEC. All exercises were performed by the non-dominant arm. MTJd of each contraction was assessed by B-mode ultrasound, and its changes over sets were compared among the groups. The average MTJd from the start to the end of six eccentric contractions in the first set was similar among the groups (6.4 ± 0.7 mm). The MTJd increased from the first to fifth set, but the increase was smaller (P < .05) for the 10%EC (13 ± 6%) and 2MVIC (16 ± 9%) groups, and CONT-2nd (3 ± 6%) when compared with CONT-1st (60 ± 12%). Both 10%EC and 2MVIC groups showed smaller (P < .05) changes in all muscle damage markers after MaxEC similarly when compared with CONT-1st, but the changes were greater than those after CONT-2nd. These results supported the hypothesis that protective effect was associated with less MTJd changes, suggesting that this is associated with the mechanisms underpinning the preconditioning effect on muscle damage.
在进行五次六次最大离心收缩（MaxEC）的最大离心运动之前两天，进行 30 次低强度（10%）离心收缩（10%EC）或两次在长肌肉长度下的最大等长收缩（2MVIC），可减少二头肌肱桡肌远肌-肌腱连接处（MTJd）在 MaxEC 离心收缩过程中的位移增加。久坐的年轻男性被随机分为对照组（CONT-1st、CONT-2nd），两组均在两周内进行两次 MaxEC 运动；或 10%EC 或 2MVIC 预处理组，两组在 MaxEC 前两天在 20°肘部弯曲处进行 10%EC 或 2MVIC。所有运动均由非优势手臂完成。使用 B 型超声评估每次收缩的 MTJd，并比较各组之间的节段变化。第一组六次离心收缩开始到结束时的平均 MTJd在各组之间相似（6.4±0.7mm）。MTJd 从第一组到第五组增加，但与 CONT-1st 相比，10%EC（13±6%）和 2MVIC（16±9%）组以及 CONT-2nd（3±6%）的增加较小（P<.05）。与 CONT-1st 相比，10%EC 和 2MVIC 组在 MaxEC 后所有肌肉损伤标志物的变化较小（P<.05），但比 CONT-2nd 后的变化更大。这些结果支持了这样的假设，即保护作用与 MTJd 变化较小有关，这表明这与预处理对肌肉损伤的机制有关。
