Potvin J R, O'Brien P R
Department of Human Biology and Nutritional Science, University of Guelph, Ontario, Canada.
Spine (Phila Pa 1976). 1998 Apr 1;23(7):774-80; discussion 781. doi: 10.1097/00007632-199804010-00006.
Surface electromyographic activities were recorded from bilateral trunk muscles as test participants maintained a 50% maximum, voluntary, isometric, lateral bend contraction to volitional exhaustion.
To challenge the trunk with a prolonged lateral bend task and observe the responses of the agonist and antagonist muscles to the resulting fatigue.
Lateral bend exertions of the trunk have been identified as a risk factor for injury to spine tissues. However, little is known about the response of spine muscles to fatigue and the subsequent implications for spine stability, joint loading, and tissue injury. Surface electromyography provides a window on muscle loading and progressive fatigue.
Eleven male participants performed a set of maximum lateral bend exertions at the start of the trial, then maintained an upright standing posture while resisting 50% of the maximum moment until volitional exhaustion, then performed another set of maximum contractions. All contractions were isometric. Measurements were made, throughout each contraction, of the lateral bend moment and abdominal and trunk extensor electromyographic activities at six bilateral surface electromyography sites. Electromyographic amplitude and mean power frequency were calculated with 500-millisecond segments recorded serially every 800 milliseconds. Mean values were calculated with data from the first and last 5% of the trial durations. Statistics determined if fatigue had a significant effect on maximum moment and the electromyographic statistics for each muscle site.
Fatigue resulted in a significant decrease in maximum lateral bend moment and increase in moment variability. Decreases in mean power frequency, indicating fatigue, were observed in three agonists (the trunk extensors) and one antagonist muscle. Unfatigued agonist electromyographic amplitudes correlated well with the mechanical advantage of muscles to generate lateral bend moments. Unfatigued antagonist activities were low except for the thoracic erector spinae. The agonists and antagonists demonstrated average increases of 17% and 8%, respectively, when pooled across muscles. Much of this change was predicted to have been associated with increases in co-contracting muscle forces.
The trunk responded to a prolonged, lateral bend contraction by increasing co-contraction as agonist trunk muscles fatigued. It was proposed that the fatigue compromised neural coordination and that the co-contraction served to maintain spine stability.
在测试参与者保持最大自主等长侧弯收缩的50%直至自愿疲劳的过程中，记录双侧躯干肌肉的表面肌电图活动。
通过长时间的侧弯任务对躯干进行挑战，并观察主动肌和拮抗肌对由此产生的疲劳的反应。
躯干的侧弯用力已被确定为脊柱组织损伤的一个危险因素。然而，关于脊柱肌肉对疲劳的反应以及随后对脊柱稳定性、关节负荷和组织损伤的影响知之甚少。表面肌电图为肌肉负荷和渐进性疲劳提供了一个窗口。
11名男性参与者在试验开始时进行一组最大侧弯用力，然后在抵抗最大力矩的50%的同时保持直立站立姿势直至自愿疲劳，然后进行另一组最大收缩。所有收缩均为等长收缩。在每次收缩过程中，在六个双侧表面肌电图部位测量侧弯力矩以及腹部和躯干伸肌的肌电图活动。肌电图幅度和平均功率频率是用每800毫秒连续记录的500毫秒时间段来计算的。平均值是用试验持续时间的前5%和后5%的数据来计算的。通过统计分析确定疲劳是否对最大力矩以及每个肌肉部位的肌电图统计数据有显著影响。
疲劳导致最大侧弯力矩显著下降，力矩变异性增加。在三块主动肌（躯干伸肌）和一块拮抗肌中观察到平均功率频率下降，表明出现了疲劳。未疲劳时主动肌的肌电图幅度与肌肉产生侧弯力矩的机械优势密切相关。除了胸段竖脊肌外，未疲劳时拮抗肌的活动较低。当汇总所有肌肉时，主动肌和拮抗肌分别平均增加了17%和8%。预计这种变化大部分与共同收缩肌肉力量的增加有关。
随着主动躯干肌疲劳，躯干通过增加共同收缩来应对长时间的侧弯收缩。有人提出，疲劳损害了神经协调，而共同收缩有助于维持脊柱稳定性。
