EFFECTS OF BODY ORIENTATION ON MAXIMUM VOLUNTARY ARM TORQUES

Introduction: Increased reliance on bulbospinal motor systems has been implicated in individuals with chronic stroke during maximum voluntary arm joint torque generation. Methods: Maximum isometric single-joint and multi-joint arm strength was observed in two body orientations (sitting and supine) while maintaining identical head/neck/trunk/extremity joint configurations in order to identify bulbospinal contributions to maximum joint torque generation in 11 individuals with stroke and 10 individuals without stroke. Results: During sitting, shoulder flexion was greater for both groups, whereas shoulder extension and elbow flexion, part of the 'flexion synergy,' were greater only in individuals with stroke. Conclusions: Body orientation influenced isometric arm strength, notably the constituents of flexion synergy in individuals with stroke, suggesting bulbospinal motor pathway involvement. From a practical perspective, clinical evaluation of single joint strength in the supine position may underestimate strength available during activities of daily living that are performed in an upright orientation. Muscle Nerve 44: 805-813, 2011