Postural reorganization induced by torso cutaneous covibration

Abstract

Cutaneous information from joints has been attributed proprioceptive properties similar to those of muscle spindles. This study aimed to assess whether vibration-induced changes in torso cutaneous information contribute to whole-body postural reorganization in humans. Ten healthy young adults stood in normal and Romberg stances with six vibrating actuators positioned on the torso in contact with the skin over the left and right external oblique, internal oblique, and erector spinae muscle locations at the L4/L5 vertebrae level. Vibrations around the torso were randomly applied at two locations simultaneously (covibration) or at all locations simultaneously. Kinematic analysis of the body segments indicated that covibration applied to the skin over the internal oblique muscles induced shifts of both the head and torso in the anterior direction (torso flexion) while the hips shifted in the posterior direction (ankle plantar flexion). Conversely, covibration applied to the skin over the erector spinae muscle locations produced opposite effects. However, covibration applied to the skin over the left internal oblique and left erector spinae, the right internal oblique and right erector spinae, or at all locations simultaneously did not induce any significant postural changes. In addition, the center of pressure position as measured by the force plate was unaffected by all covibration conditions tested. These results were independent of stance and suggest an integrated and coordinated reorganization of posture in response to vibration-induced changes in cutaneous information. In addition, combinations of vibrotactile stimuli over multiple locations exhibit directional summation properties in contrast to the individual responses we observed in our previous work.

Figure 1.

Diagram and digital image of the 18 passive markers and six C2 tactor locations applied to the body and a digital image of a C2 tactor.

Figure 2.

Average maximum AP displacement across all participants as a function of the covibration condition during the normal stance for pre-vibration (blue) and per-vibration (red) periods. A, B IO. B, B ES. C, L IO-ES. D, R IO-ES. E, ALL. Blue and red circles represent average AP maximum displacements of body landmarks (i.e., head, C7, L5/S1, and knee). Positive values are defined as displacement in both the anterior and vertical directions. Shaded areas represent SE of the corresponding average maximum AP displacements. Bird's-eye view drawings illustrate the covibration conditions.

Figure 3.

A, Computation of each joint angle in the AP direction. Each circle indicates the marker location at the head, C7, L5/S1, knee, and ankle. Subplot indicates the scale and direction of angles. B, Average maximum AP joint angles across all participants during normal stance. White and gray bars correspond to the B IO and B ES covibration conditions, respectively. Error bars indicate SE, and numbers inside the bars indicate the corresponding average.

Figure 4.

Average AP anchoring index for body segments (head, torso, and upper leg) across all participants as a function of the covibration location during normal stance. White and gray bars correspond to the B IO and B ES covibration conditions, respectively. Error bars indicate SE, and the numbers inside the bars indicate the corresponding average values.