ヒトの随意運動にみられる筋活動電位の抑制現象に関する研究第II報 2関節同時運動時,二関節筋に現われる抑制現象について

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  • Inhibition of Muscular Electrical Activity during Voluntary Movement in Man I. I Electrical Inhibition in Bifunctional Muscles during Voluntary Biarticular Leg Movement

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Electrical silence which appeared in bifunctional leg muscles during simultaneous hip and knee extensions under isometric condition was investigated in terms of the neurophysiological and dynamical features in the biarticular movement.<BR>Subjects employed in the experim ents were healthy adult males ranging in age from 19 to 40, and they have no special training experiences for sports activity. Experimental posture was supine with both hip and knee joints kept at 90 degree angles. Electromyograms (EMGs) were recorded by conventional method using surface electrodes.<BR>Part 1. Electrical inhibition in the bifunctional knee extensor during simultaneous extensions of hip and knee joints<BR>Simultaneous hip and kn ee extensions were performed along two distinctly different functional force directions, so that the resultant force output was limited by the hip joint force in one direction, and by the knee joint force in another. EMGs were recorded from the Rectus lemons (Rf), the Vastus medialis (Vm) and the Semimembranosus (Sm), and potentials evok ed by the patella tendon jerk were recorded from the Rf and the Vm. The total leg extension force exerted at the sole and the mechanical impact of the tendon tapping were recorded simultaneously with the EMGs and the evoked potentials.<BR>When the total leg extension force was limited by the hip extension force, the amplitude of the evoked potential from the Rf decreased while the leg extension force gradually increased. The Sm showed a marked discharge in this case. The results obtained in the experiment suggested that there was an inhibitory input to the a-motoneurone pool innervating the Rf, and this was probably due to an antagonistic inhibition induced by the increased activity in the hamstring muscles like the Sm. When the total leg extension force was limited by the knee extension force, the evoked potential from the Rf remained unchanged, and no discharge was observed in the Sm. The amplitude of the evoked potential from the Vm tended to increase with the increases in the resultant leg extension forces exerted along both functional force directions. Thus, the appearance of the electrical inhibition in the Rf was depending on whether or not the hip joint force was limiting the resultant leg extension force.<BR>Part 2. Electrical inhibition in bifunctional muscles and its effects on recruitment of monofunctional muscles during voluntary biarticular leg movement<BR>Discharges of the hip extensors, the Gluteus maximus (Gm), the Adductor magnus (Am), the Biceps femoris (Bf), the Semitendinosus (St) and the Sm, and those of the knee extensors, the Vm, the Vastus lateralis (Vl), the Rf and the Tensor fasciae latae (Tfl) were integrated through the Miller Circuit and recorded with their raw EMGs. A constant load (60 max.)was applied isometrically at the distal end of the thigh against the hip extension during application of graded load (10∼60% max. ) at the ankle joint against the knee extension (Exper.1). A constant load (60% max. ) was applied against the knee extension, and graded loads (10∼60% max.) were applied against the hip extension (Exper.2). Individual hip extension (Exper.3-A) and knee extension (Exper.3-B) were performed against constant loads (60%max.) as references to the Expers.1 and 2.<BR>Although the constant load was applied against the hip extension, the integrated EMGs (IEMGs) of the bifunctional hip extensors of the Bf, the St and the Sm decreased with the increasing load against the knee extension in the Exper.1. Also in the Exper.2, the IEMGs of the bifunctional knee extensors of the Rf and the Tfl decreased with the increasing load against the hip extension. These decreases in the IEMGs of the bifunctional muscles might be due to an antagonistic inhibition induced by the increase in activities of the antagonistic muscles.<BR>While the constant load was applied, the monofunctional agonistic extensors of the Vm and the Vi increased their activities.

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