Brown D A, Kautz S A, Dairaghi C A
Rehabilitation Research and Development Center, V.A. Palo Alto Health Care System, California 94304, USA.
Brain. 1997 May;120 ( Pt 5):825-37. doi: 10.1093/brain/120.5.825.
With hemiplegia following stroke, a person's movement response to anti-gravity posture often appears rigid and inflexible, exacerbating the motor dysfunction. A major determinant of pathological movement in anti-gravity postures is the failure to adapt muscle-activity patterns automatically to changes in posture. The aim of the present study was to determine whether the impaired motor performance observed when persons with hemiplegia pedal in a horizontal position is exacerbated at more vertical anti-gravity body orientations. Twelve healthy elderly subjects and 17 subjects with chronic (> 6 months) post-stroke hemiplegia participated in the study. Subjects pedalled a modified ergometer at different body orientations (from horizontal to vertical), maintaining the same workload, cadence, and hip and knee kinematics. Pedal reaction forces, and crank and pedal kinematics, were measured and then used to calculate the work done by each leg and their net positive and negative components. The EMG was recorded from four leg muscles (tibialis anterior, medial gastrocnemius, rectus femoris and biceps femoris). The main result from this study was that impaired plegic leg performance, as measured by net negative work done by the plegic leg and abnormal early rectus femoris activity, was exacerbated at the most vertical body orientations. However, contrary to the belief that muscle activity cannot adapt to anti-gravity postures, net positive work increased appropriately and EMG activity in all muscles showed modulated levels of activity similar to those in elderly control subjects. These results support the hypothesis that increased verticality exacerbates the already impaired movement performance. Yet, much of the motor response to verticality was flexible and appropriate, given the mechanics of the task.
中风后出现偏瘫时，患者对反重力姿势的运动反应往往显得僵硬且缺乏灵活性，从而加剧了运动功能障碍。反重力姿势下病理性运动的一个主要决定因素是无法自动使肌肉活动模式适应姿势变化。本研究的目的是确定偏瘫患者在水平位置蹬踏板时观察到的运动表现受损情况在更垂直的反重力身体姿势下是否会加剧。12名健康老年受试者和17名患有慢性（>6个月）中风后偏瘫的受试者参与了该研究。受试者在不同身体姿势（从水平到垂直）下蹬踏一台改良的测力计，保持相同的工作量、踏频以及髋部和膝部运动学特征。测量踏板反作用力、曲柄和踏板运动学特征，然后用于计算每条腿所做的功及其净正、负分量。从四块腿部肌肉（胫前肌、腓肠肌内侧头、股直肌和股二头肌）记录肌电图。本研究的主要结果是，以偏瘫腿所做的净负功和股直肌早期异常活动来衡量，偏瘫腿的功能受损在最垂直的身体姿势下会加剧。然而，与肌肉活动无法适应反重力姿势这一观点相反，净正功适当增加，并且所有肌肉的肌电图活动显示出与老年对照受试者类似的活动调节水平。这些结果支持了这样一种假设，即垂直度增加会加剧本已受损的运动表现。然而，考虑到任务的力学原理，对垂直度的许多运动反应是灵活且适当的。
