The influence of external loads on movement precision during active shoulder internal rotation movements as measured by 3 indices of accuracy.

CONTEXT Using constant, variable, and absolute error to measure movement accuracy might provide a more complete description of joint position sense than any of these values alone. OBJECTIVE To determine the effect of loaded movements and type of feedback on shoulder joint position sense and movement velocity. DESIGN Applied study with repeated measures comparing type of feedback and the presence of a load. SETTING Laboratory. PATIENTS OR OTHER PARTICIPANTS Twenty healthy subjects (age = 27.2 +/- 3.3 years, height = 173.2 +/- 18.1 cm, mass = 70.8 +/- 14.5 kg) were seated with their arms in a custom shoulder wheel. INTERVENTION(S) Subjects internally rotated 27 degrees in the plane of the scapula, with either visual feedback provided by a video monitor or proprioceptive feedback provided by prior passive positioning, to a target at 48 degrees of external rotation. Subjects performed the internal rotation movements with video feedback and proprioceptive feedback and with and without load (5% of body weight). MAIN OUTCOME MEASURE(S) High-speed motion analysis recorded peak rotational velocity and accuracy. Constant, variable, and absolute error for joint position sense was calculated from the final position. RESULTS Unloaded movements demonstrated significantly greater variable error than for loaded movements (2.0 +/- 0.7 degrees and 1.5 +/- 0.4 degrees, respectively) (P < .05), but there were no differences in constant or absolute error. Peak velocity was greater for movements with proprioceptive feedback (45.6 +/- 2.9 degrees/s) than visual feedback (39.1 +/- 2.1 degrees/s) and for unloaded (47.8 +/- 3.6 degrees/s) than loaded (36.9 +/- 1.0 degrees/s) movements (P < .05). CONCLUSIONS Shoulder joint position sense demonstrated greater variable error unloaded versus loaded movements. Both visual feedback and additional loads decreased peak rotational velocity.