Dynamic movement of center of gravity with hand grip

Abstract

We studied the movement of center of gravity (CG) in young and aged subjects during maximum grip of right or left hand. Body-sway was recorded with stabilometry in rest-stand position and in maximum grip. The data from right-or left-handed young subjects were analyzed. Maximum grip power was not different between dominant hand and un-dominant hands. Total length (LNG) and total movement area of CG (REC AREA) during the measurements were significantly larger in maximum grip than in rest-stand. In right-handed subjects, LNG increased to 245% and 250% of rest-stand value, and REC AREA increased to 589% and 633% in right and left hand grip, respectively. In left-handed subjects, LNG increased to 186% and 188% of rest-stand value, and REC AREA increased to 400% and 533% in right and left hand grip, respectively. No significant difference of LNG and REC AREA was observed between right and left hand grip in either hand dominant subject. Maximum grip did not affect CG in rest-stand. In aged subjects, maximum grip power was significantly less than in young subjects (48%). LNG and REC AREA in rest-stand were significantly larger in aged subjects than in young subjects (220% and 400%, respectively). They were not different during maximum grip with either hand. While aged subjects have difficulty of controlling CG in rest-stand, they have less problems to stabilize CG during maximum grip. These data indicated that dynamic movement of CG might be important to understand person's activity of daily living.The shift of center of gravity (CG) in rest-stand has been considered a key factor of daily living, since unbalanced movement causes tumbling or dizziness (1, 3). The fact that eye closing increased CG movement suggested that sensory inputs were important for CG stability (8). Signals from the cerebral cortex and cerebellum to individual muscles were another important factor in CG control (3, 9). Dynamic body movement required coordination of many muscle contractions and/or relaxations (9). Different parts of the brain were activated during dynamic movement, including the primary motor cortex, sensory cortex, striate body and cerebellum (3). Since many muscle contractions are integrated in the nervous system, CG might sway during dynamic movement.Measurements and analyses of CG have been developed over the past two decades (2,5,7,8). The concept of "body-sway" has been widely used; while a subject stood at the computer-operated stabilometry, CG was analyzed instantaneously. Total movement of CG during the measurement was traced by a computer and calculated. At the same time, moving area, horizontal component and vertical component were calculated (5). This newly developed stabilometry could demonstrate dynamic movement of CG more accurately than ever before.

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