Revising Repositioning for Valid Measurement of Human Position Sense

Kurzfassung

Active elbow repositioning is used to assess limb position sense and typically yields small errors. Because target angle and movement history normally covary, it remains unclear whether these errors reflect remembered target-position accuracy independently of that history. In two experiments with 12 healthy adults each, participants reproduced 50°, 60°, and 70° target angles without vision under three within-subject conditions. In the standard condition, presentation and reproduction shared the same starting position. In the altered memorisation trajectory, an intermediate angle was inserted into the passive movement to and from the target, whereas in the altered reproduction trajectory, active reproduction began at this position. The intermediate angle varied in Experiment 1 and was fixed at 0° in Experiment 2. Repeated-measures ANOVAs examined signed and absolute error and their intra-individual variability. Each manipulation increased signed error variability in both experiments. Only the altered memorisation trajectory produced a replicated extension bias, whereas the flexion-directed shift under the altered reproduction trajectory reached significance only in Experiment 1. The results indicate that repositioning error does not isolate remembered target-position accuracy from movement history. Active elbow repositioning therefore cannot be interpreted as a valid context-independent indicator of human limb position sense. Small repositioning errors reflect the accuracy of memory-guided reproduction within a specific movement history rather than target-position accuracy alone.