Relationship between Trunk Motor Function and Changes in Center of Pressure during Lateral Shift of Center of Gravity in Sitting Hemiplegic Patients

Abstract

The purposes of this study were to examine the relationship between trunk motor function and changes in the center of pressure (COP) during fast lateral bending in sitting, and to investigate the relationship between these changes and the ability to walk in hemiplegic patients. Subjects were thirty-three hemiplegic patients (right hemiplegia, 17; left hemiplegia, 16; age, 63 ± 12 years). The directions of the motion were measured on both the paralyzed and healthy sides of the body.
The COP displacement in right-left direction was detected by means of force plates at a sampling rate of 500 Hz. COP trajectories moved in the opposite direction of the motion immediately after a starting signal. Thereafter these trajectories rapidly moved in the direction of the motion. The maximum amplitude of the initial COP shift and the maximum velocity of the COP were defined as A₁ and V_max, respectively. The distance that the COP moved from the neutral position to the maximum shift position was defined as D_cog. Trunk motor function in hemiplegia was evaluated using the neck, trunk and pelvic motor function test (NTP), which was classified into six stages. In addition, the degree of hemiplegia with which walking remains possible was determined using the 10-meter walking speed.
The correlation between A₁ in both directions and NTP stage was significant (p < 0.01). The subjects above NTP stage 4 tended to have a larger A₁ value than the other hemiplegic patients. The relationship between V_max in both directions and NTP stage was also significant (p < 0.01). The correlation between D_cog in the healthy side and NTP stage was significant (p < 0.05), while the correlation between D_cog in the paralyzed side and NTP stage was not. The relationship between walking speed and A₁ in the healthy side was significant (p < 0.05). while that in the paralyzed side was not. The correlation between walking speed and D_cog was significant (p < 0.01).
It was thought that the hemiplegic patients with good trunk motor function were able to produce the moment of gravity for fast movement. Moreover, lower limb stability may induce a larger center of gravity shift. The relation between walking speed and A₁ is thought to be influenced by the condition of the lower limb in addition to pelvis elevation. The results indicated that analysis of changes in COP during fast lateral bending in sitting is useful for evaluation of trunk motor function.