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Updated: May 28, 2026

Method to Measure Tone of Axial and Proximal Muscle
Published on: December 14, 2011
Effects of body orientation on maximum voluntary arm torques
Daniel M Krainak1, Michael D Ellis, Kathryn Bury
1Department of Physical Therapy and Human Movement Sciences, Northwestern University, 645 North Michigan Avenue, Suite 1100, Chicago, Illinois 60611, USA.
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.
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