Applied Neuromuscular Physiology Laboratory, Oklahoma State University, Stillwater, OK, USA.
School of Kinesiology & Physical Therapy, University of Central Florida, Orlando, FL, USA.
Physiol Rep. 2021 Jan;9(1):e14677. doi: 10.14814/phy2.14677.
Skeletal muscle disuse results in rapid functional declines. Previous studies have typically been at least 1 week in duration and focused on the responsiveness of men. Herein, we report the timeline of initial impairments in strength, voluntary activation (VA), and motor unit control during 2 weeks of knee joint immobilization. Thirteen women (mean age =21 years) underwent 2 weeks of left knee joint immobilization via ambulation on crutches and use of a brace. Participants visited the laboratory for testing on seven occasions (two familiarization visits, pretest, 48 and 72 h, 1 and 2 weeks). Knee extensor isometric and concentric isokinetic strength at two velocities (180 and 360 degrees⋅s ), VA, and submaximal vastus lateralis motor unit activity were evaluated. Moderate-to-large decreases in isometric and concentric strength at 180 degrees⋅s and VA were observed within 48 hours. Isometric strength continued to decline beyond 72 h, whereas other variables plateaued. The B-term of the motor unit mean firing rate versus action potential amplitude relationship demonstrated a moderate increase 1 week into immobilization, suggesting that greater firing rates were necessary to maintain pretest torque levels. Concentric strength at a velocity of 360 degrees s was not affected. Decreases in knee extensor strength occur within a matter of days after immobilization, although the time course and magnitude vary among assessment methods. These changes are mediated by the nervous system's capacity to activate skeletal muscle. Clinically appropriate interventions which target nervous system plasticity should be implemented early to minimize the rapid functional impairments associated with disuse.
骨骼肌废用会导致功能迅速下降。以前的研究通常持续至少 1 周，且侧重于男性的反应性。在此，我们报告了在 2 周膝关节固定期间，力量、自愿激活（VA）和运动单位控制的初始损伤的时间进程。13 名女性（平均年龄 21 岁）通过拐杖步行和使用支具进行左膝关节固定 2 周。参与者在 7 次就诊时到实验室进行测试（2 次熟悉就诊、预测试、48 小时和 72 小时、1 周和 2 周）。评估了膝关节等长和向心等速的最大力量（180 和 360 度·s）、VA 和次最大股外侧肌运动单位活动。在 48 小时内观察到 180 度·s 的等长和向心强度以及 VA 的中等至大幅度下降。等长强度在 72 小时后继续下降，而其他变量则趋于平稳。运动单位平均放电率与动作电位幅度关系的 B 项在固定 1 周时表现出适度增加，这表明为了保持预测试的扭矩水平，需要更高的放电率。360 度·s 的向心强度不受影响。膝关节伸肌力量在固定后几天内就会下降，尽管在不同的评估方法中，时间进程和幅度有所不同。这些变化是由神经系统激活骨骼肌的能力介导的。应尽早实施针对神经系统可塑性的临床适当干预措施，以尽量减少与废用相关的快速功能损伤。
