McGill S M, Hughson R L, Parks K
Faculty of Applied Health Sciences, Department of Kinesiology, University of Waterloo, Canada.
Ergonomics. 2000 Apr;43(4):486-93. doi: 10.1080/001401300184369.
Owing to the recent interest in torso stabilization exercises together with many questions regarding the duration of prolonged isometric holds in occupational settings, the authors attempted to assess the level of back muscle oxygenation during prolonged isometric contractions. Specifically, this study recorded relative oxygen saturation of haemoglobin/myoglobin using Near Infrared Spectroscopy (NIRS) in the L3 erector mass during prolonged isometric contractions at intensities from 2 to 30% of maximum voluntary contraction (MVC). It was hypothesized that available oxygen to these muscles is severely compromised even at moderate levels of activation observed in occupational work. Eight volunteers without a history of lower back pain or injury participated in this study. The exercise task involved isometric contraction of the lower erector spinae at five different levels of each subject's maximal voluntary contraction: 2, 5, 10, 20 and 30% MVC, presented in random order. Subjects were placed in a sitting position, with a curved plastic plate secured horizontally to the pelvis to minimize movement at the hip joint. During extensor exertions, they were restrained with a harness that was attached at chest level to a load cell. Each isometric contraction was performed for 30 s followed by 1 min of rest. All levels of contraction demonstrated reduction in oxygen. Given the concern for motion artefact on the NIRS signal, sham trials were conducted where the subjects went through the procedure of attaching the pulling cable but no active pull was performed. These trials showed no change in the NIRS signal. At this time NIRS appears to be the only non-invasive instrumentation available to indicate total available muscle oxygen during low level, prolonged work. Although the specific tissue volume sampled by NIRS cannot be positively identified, it appears that tissue oxygenation in the lumbar extensor musculature is reduced as a function of contraction intensity, even at levels as low as 2% of MVC. These data have implications for prolonged work where postures requiring isometric contractions are sometimes held for hours, and where musculoskeletal illness has been linked to prolonged contraction levels above 2%MVC--these data suggest a possible biological pathway.
由于近期人们对躯干稳定训练的关注，以及在职业环境中关于长时间等长收缩持续时间的诸多问题，作者试图评估长时间等长收缩过程中背部肌肉的氧合水平。具体而言，本研究使用近红外光谱（NIRS）记录了在最大自主收缩（MVC）强度的2%至30%下进行长时间等长收缩时，L3竖脊肌中血红蛋白/肌红蛋白的相对氧饱和度。据推测，即使在职业工作中观察到的中等激活水平下，这些肌肉可利用的氧气也会严重受损。八名无下背痛或损伤史的志愿者参与了本研究。运动任务包括在每个受试者最大自主收缩的五个不同水平（2%、5%、10%、20%和30%MVC）下进行下竖脊肌的等长收缩，顺序随机。受试者坐在座位上，一块弯曲的塑料板水平固定在骨盆上，以尽量减少髋关节的活动。在伸展用力时，他们用一个固定在胸部水平的负荷传感器的背带进行约束。每次等长收缩持续30秒，然后休息1分钟。所有收缩水平均显示氧气减少。鉴于担心NIRS信号上的运动伪影，进行了假试验，即受试者经历连接牵引电缆的过程，但不进行主动牵引。这些试验显示NIRS信号没有变化。此时，NIRS似乎是唯一可用于指示低水平、长时间工作期间肌肉总可用氧气的非侵入性仪器。尽管无法确切确定NIRS采样的具体组织体积，但似乎腰椎伸肌组织中的组织氧合随着收缩强度的增加而降低，即使在低至MVC的2%的水平也是如此。这些数据对于长时间工作具有启示意义，在长时间工作中，需要等长收缩的姿势有时会保持数小时，并且肌肉骨骼疾病与高于2%MVC的长时间收缩水平有关——这些数据提示了一条可能的生物学途径。
