筋電図学的に見た上腕二頭筋の遠心性収縮の閾値

The Threshold of Eccentric Contraction in the Biceps Brachi Muscle in Man by Means of Electromyography

要旨：この研究の目的は，上腕二頭筋の遠心性収縮の発現が肘関節伸展運動に伴う上腕三頭筋の収縮増大とどの様な関係にあるか，また肘関節伸展開始角度の違いによる影響をうけるかを，筋電図と筋力を指標に調査することである．肘関節の伸展運動角度の増大に伴って，上腕二頭筋筋電位の発現経過は，第1相の小さな振幅が持続している期間と第2相の振幅が著明に高くなる期間の2相に分かれた．第1相の電位振幅の高さは，前腕の重さを重力に対して補償し肘伸展を行わせた時の電位振幅とほぼ同じであった．第2相の出現に要する肘伸展運動に抗する力は，平均4.54kg重であった．この値から前腕の重さ(平均1.3kg重)を差し引いた約3kg重が，臨床上関心の持たれる遠心性収縮の出現閾値であろう．以上の結果は肘関節伸展開始角度の違いからはほとんど影響を受けなかった．

　Characteristics of eccentric muscle contraction appearing in biceps muscles of the upper arm when the subject was asked to extend his forearm against resistance voluntarily with different starting extense position of the forearm were studied electromyographically and from muscular strength. When the forearm was extended gradually, there were two different time courses of the electromyogram in the eccentric muscle contraction of the biceps; one is an early period of sustaining low amplitude of electromyogram and the other, a later period of marked growth to a high amplitude. The level of the low amplitude in the early period was virtually the same as the that recorded in the biceps muscles under the condition of removing the body weight of the forearm. Meanwhile the force of the forearm against the resistance in producing the high amplitude of the later period was 4.5 kilograms weight in mean value. Then the 3 kilograms weight, which is the outcome of the substraction of 1.3 kilograms body weight of the forearm from this figure, could be estimated as the weight of appearing threshold of the eccentric contraction handled in the clinical field. These results were not effected by any difference of the starting extended position of the forearm.