Institute of Sport Science, University of Rostock, Ulmenstrasse 69 - House 2, 18057 Rostock, Germany.
J Electromyogr Kinesiol. 2011 Apr;21(2):340-7. doi: 10.1016/j.jelekin.2010.10.002. Epub 2010 Nov 2.
Altered biomechanical demands of a stabilization task lead to specific changes in coordination patterns among the involved muscles. The objective of this work was to investigate the effects of increased Degrees of Freedom (DoF) of an external object on the stabilization process of the ankle joint in a voluntary force production task. Four muscles (vastus medialis, VM; tibialis anterior, TA; peroneus longus, PL; gastrocnemius medialis, GM) were recorded using surface electromyography and synchronized to dynamometric data. The subject's task was to exert force against the external object by performing a knee extension under 0, 1 or 3 DoF. Forces were measured using three dimensional force transducers and temporal coordination was assessed using the cross-correlation function (CCF). While the force decreased with increasing DoF the muscles showed a selective gain scaling in order to stabilize the ankle joint. Muscles fulfilling mainly stabilizing functions (TA and PL) tended to increase their activities, while the muscles with motor functions either decreased (GM) or increased (VM). The CCF revealed different intermuscular coordination strategies depending on the environmental condition, showing an advanced phasing in the ankle stabilizing PL in unstable environmental conditions (3 DoF). Nevertheless, the overall sequence of muscle activation was preserved. It is concluded that the process of joint stabilization is controlled in dependency of the status of the external system. The associated neuromuscular system adjustments underline the role of movement coordination in the stabilization process.
稳定任务的生物力学需求变化会导致相关肌肉的协调模式发生特定变化。本工作的目的是研究增加外部物体自由度（DoF）对自愿力产生任务中踝关节稳定过程的影响。使用表面肌电图记录了 4 块肌肉（股直肌、胫骨前肌、腓骨长肌、比目鱼肌），并与测力数据同步。受试者的任务是在 0、1 或 3 自由度下进行膝关节伸展，以对抗外部物体施加的力。使用三维力传感器测量力，通过互相关函数（CCF）评估时间协调。随着自由度的增加，力减小，而肌肉表现出选择性的增益缩放以稳定踝关节。主要起稳定作用的肌肉（胫骨前肌和腓骨长肌）往往会增加其活动，而具有运动功能的肌肉则减少（比目鱼肌）或增加（股直肌）。CCF 显示出不同的肌肉间协调策略取决于环境条件，在不稳定的环境条件（3DoF）下，踝关节稳定的 PL 表现出提前相位。然而，肌肉激活的整体顺序得以保留。结论是，关节稳定过程受外部系统状态的控制。相关的神经肌肉系统调整强调了运动协调在稳定过程中的作用。
