Myers Joseph B, Riemann Bryan L, Ju Yan-Ying, Hwang Ji-Hye, McMahon Patrick J, Lephart Scott M
Neuromuscular Research Laboratory, Musculoskeletal Research Center, Department of Orthopaedic Surgery, University of Pittsburgh, Pittsburgh, PA, USA.
Clin Orthop Relat Res. 2003 Feb(407):92-101. doi: 10.1097/00003086-200302000-00017.
Previous research in relaxed muscles shows that muscle reflex latencies are too slow to protect the shoulder. However, during athletic activity when injury occurs, some level of shoulder muscle contraction typically exists. The purpose of the current study was to assess shoulder muscle reflex latencies under various levels of muscle contraction. Seventeen healthy subjects participated. A perturbation consisting of an external rotation collision force to the anterior forearm in a position of apprehension under various levels of muscle contraction (0%, 20%, and 50% of a maximum voluntary muscle contraction) was applied. Muscle reflex latencies were measured as the time from perturbation application to onset of muscle activity. Electromyography measured activity onset of the rotator cuff muscles and the primary humeral movers. During 0%, the latissimus dorsi muscle reflex latency was significantly slower than most other muscles. No difference existed between muscles in the 20% and 50% conditions. For the rotator cuff muscles, the reflex latencies significantly quickened for 20% and 50% compared with the relaxed state (0%). Overall, introducing muscle contraction significantly quickened muscle reflex latencies. These results provide clinicians with a better understanding of the role that these reflexes play in joint stability in a position of injury vulnerability like a position of apprehension.
先前对放松肌肉的研究表明，肌肉反射潜伏期过慢，无法保护肩部。然而，在运动活动中受伤时，肩部肌肉通常会有一定程度的收缩。本研究的目的是评估不同肌肉收缩水平下的肩部肌肉反射潜伏期。17名健康受试者参与了研究。在不同肌肉收缩水平（最大自主肌肉收缩的0%、20%和50%）下，对处于恐惧位的前臂施加由外旋碰撞力组成的扰动。肌肉反射潜伏期测量为从施加扰动到肌肉活动开始的时间。肌电图测量了肩袖肌肉和主要肱骨运动肌的活动开始时间。在0%时，背阔肌的反射潜伏期明显慢于大多数其他肌肉。在20%和50%的情况下，各肌肉之间没有差异。对于肩袖肌肉，与放松状态（0%）相比，20%和50%时的反射潜伏期明显加快。总体而言，引入肌肉收缩显著加快了肌肉反射潜伏期。这些结果让临床医生更好地理解了这些反射在诸如恐惧位等易受伤关节位置的稳定性中所起的作用。
