Short-term limb immobilization affects motor performance

Abstract

C. Ghez, J. Gordon, and M. R Ghilardi (1995; J. Gordon, M. R Ghilardi, & C. Ghez, 1995; R. L. Sainburg, M. R Ghilardi, H. Poizner, & C. Ghez, 1995) have found that proprio-ceptive deafferentation impairs feedforward and feedback mechanisms that control reaching movements. In the present study, the authors found immobilization-induced changes in limb kinematics, including joint motion, in 32 healthy participants who performed out-and-back movements before and after 0, 6, or 12 hr of immobilization of the left arm. Control participants did not undergo the arm immobilization procedure. Immobilization for 12 hr, but not 6 hr, caused trajectories with increased hand-path areas and altered interjoint coordination. The abnormalities were smaller in amplitude but similar in quality to those reported in deafferented patients (R. L. Sainburg et al.). In addition, movement onset point significantly drifted after immobilization. Thus, short-term limb disuse can affect interjoint coordination by acting on feedforward mechanisms. These behavioral alterations are potentially related to cortical plastic changes.

FIGURE 1

(A) Shoulder (S) and elbow (E) angles at beginning of each block. When movement onset was located in the center of the tablet, the angles measured 45° and 90°, respectively. (B) Representative hand paths for one participant at baseline, with and without visual feedback, to targets at 45°, 90°, and 135°. FB = feedback.

FIGURE 2

The drift of movement starting point across trials differed in the three groups. (A) Mean onset point at end of baseline (open circles) and test (closed circles). Ellipses indicate standard errors. Notice the difference between baseline and test in the 12-hr immobilization (IMM) group. The distribution of onset points differed significantly only in that group. (B) Graphical representation of joint displacement. Dotted lines represent starting limb configuration, thin and thick black lines represent the average of limb configurations at end of baseline and end of test, respectively. (C) Difference between test and baseline in each cycle of six movements for movement onset point and for elbow and shoulder angles. That difference, which represents the change of the drift between test and baseline, was significantly higher in the 12-hr IMM group than in the other groups.

FIGURE 3

Hand-path changes at test. (A) Representative trajectories to 45° target for a representative participant from each group at test. (B) Mean normalized hand-path area for the three groups at baseline (open bars) and at test (closed bar). At test, mean normalized area slightly decreased in controls and increased slightly after 6 hr of immobilization (IMM 6 group) and consistently after 12 hr (IMM 12 group). (C) Variability of normalized hand-path area across the three target directions (standard deviation of the mean). That parameter significantly increased at test only after 12 hr of immobilization. (D) Variability of interjoint timing (IJT) increased after 12 hr of immobilization.