外乱負荷刺激に対するPrecision Grip(精密把握)の調節

The Infiuences of Load Force Perturbations on the Control of Precision Grip during Lifting Task

要旨：物体保持中の力の調節機構の機序を明らかにするために，健常者7名を対象に外乱負荷刺激のPrecision Grip(PG：精密把握：以下つまみ)におよぼす影響を調べ，以下のことが得られた．①外乱負荷刺激の増加にともない，つまみ力は増加した．また，刺激後のつまみ力最大値に対する安定つまみ力の割合は，減少傾向を示した．②外乱負荷刺激により生じた重力方向への力に対し母指球筋群，第一背側骨間筋の筋電図の振幅は増加した．③開眼時では，外乱負荷刺激を加えてからのつまみの立ち上がり，および筋電図の発現するまでの時間がともに閉眼時のものに比べ短かった．以上の成績から，つまみ力の調節に体性感覚，視覚情報が重要であることが示唆された．

　This study examines the influence of somatosensory and visual information on the control of precision grip between the thumb and the index finger. Grip force and electromyogram (EMG) of the thenar muscles and the first dorsal interosseous were measured in seven healthy subjects (mean age:28 years old) with eyes opened and closed. When load force was applied suddenly to the grip apparatus, subjects were asked to lift up the apparatus in space with as much lessor grip strength as possible. The apparatus consists of two parallel planes. At the lower end of the two planes strain gauges were attached for measuring grip force. Results were as follows : 1) An increase of perturbation in vertical load force brings about increase of precision grip force. During the lifting of the grip apparatus, there was a parallel increase in the precision grip force and load force as previously described. A static phase was attained after the minimum grip force was reached. 2) In separate lifting experiments, an EMG was recorded on the first dorsal interosseous and the thenar muscles. Perturbation in vertical load force caused an increase of EMG amplitude. Automatic muscle responses of the wrist were triggered by the impact. 3) With eyes opened, the precision grip force after impact and appearance EMG amplitude occurred sooner than with the eyes closed. 4) With eyes opened, the precision grip force increased prior to impact. This increase began at about 60ms-150 ms before the onset of load force. There was also a preparatory lifting of the pinch apparatus during the time when the preparatory pinch force increased.

　The present results show that somatosensory information and visual cues have an important role in the control of precision grip during lifting tasks.