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本研究の目的は,立位での前かがみ姿勢で引き上げ運動を行う際に体幹前傾角度の違いが体幹および股関節伸展筋の活動に及ぼす影響を明らかにすることである。対象は19歳から29歳までの健常男性10名(平均年齢:23.1歳)とした。導出筋は腹直筋,腹斜筋群,L3,L5レベル脊柱起立筋,広背筋,大殿筋,大腿二頭筋とした。運動課題は体幹前傾30°,45°,60゜にてピークフォースのO%,30%,60%を行うこととした。筋電図の平均積分値は最大随意収縮(Maximal voluntary contraction ; MVC)を基準に正規化した(%MVC)。その結果,すべての筋で,いずれの前傾角度でも負荷が大きいほど%MVCは有意に大きかった。同一負荷では体幹前傾角度が大きいほど脊柱起立筋の%MVCは小さく,広背筋と大腿二頭筋の%MVCは大きかった。これらの結果から,脊柱起立筋活動が減少するような前かがみ姿勢では腰部の受動的な組織の負担は増していると考えられるが,肩関節や股関節伸展筋が活動量を増やして引き上げ運動を行っていることが示唆された。
The purpose of this study was to clarify the influence of difference in the angle of forward trunk inclination on the activity of trunk and hip extensor muscles, in the forward bending posture, which was observed while doing isometric pulling up. Ten healthy male volunteers (mean age: 23.1 years, range: 19-29 years) participated in this study. Surface electromyography (EMG) was recorded during the contraction of the rectus abdominus (RA), abdominal obliques (AO), L3 erector spinae of L3 (L3 ES), L5 erector spinae (L5 ES), latissimus dorsi (LD), and biceps femoris (BF) muscles. The tasks involved pulling up a load at 0%, 30% and 60% of peak force with 30°, 45° and 60° inclination of the trunk in relation to the vertical line. The average EMG values were calculated during the tasks, and they were then normalized relative to the values obtained during the maximum voluntary contractions (%MVC). The results showed that the %MVC of all muscles increased in accordance with an increase of the load in all inclinations of trunk. The %MVC of L3 ES and L5 ES decreased in accordance with the increase of forward inclination with the same load. The %MVC of LD and BF increased in accordance with the increase of forward inclination with the same load. The results suggest that the electromyographic activity of shoulder and hip extension may increase when the activity of the ES decreases and the stress of lumbar passive tissues may increase, which is observed while pulling up the load in the forward bending posture.
