Direction-dependent misalignment between joint and muscle spaces predicts different generalization patterns following adaptation to opposing visuomotor rotations

Directional alignment between joint and muscle spaces is posture- and direction-dependent, and this misalignment predicts distinct visuomotor generalization patterns after clockwise versus counterclockwise rotations.

• Why it matters: Joint-based intrinsic representations may miss how muscle activation maps onto joint motion, leaving unclear how biomechanics shape motor learning generalization.
• What they did: In Experiment 1, EMG from nine upper-limb muscles during planar reaching in two workspaces (separated by a 45° shoulder rotation) showed joint-aligned directions were not always muscle-aligned, varying by movement direction. In Experiment 2, generalization after visuomotor adaptation to clockwise versus counterclockwise rotations was tested and compared to joint-space predictions.
• The result: Experiment 2 found a systematic shift between clockwise and counterclockwise generalization patterns, matching the muscle-pattern similarity-based prediction rather than the identical joint-space account.

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