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- 朝野裕一
二つの関節を跨ぐ筋肉〜二関節筋:第五話
二関節筋のハムストリングス、
それに拮抗する大腿四頭筋の中にも大腿直筋という二関節筋があります
骨盤に付いていて股関節を跨いで膝関節をも跨ぎ、すねの骨(脛骨)
に膝蓋骨(お皿の骨)を介して止まっています。
ハムストリングスと拮抗しているので、その作用=働きはそれと全く
逆になり、
膝を伸ばすこと、骨盤を前に引っ張ることと股関節を曲げることです。

上の図のように、仰向けで横になっている状態から、 膝をある一定の
角度に保持しながら上に持ち上げる動きはまさしく、大腿直筋の作用
です。
膝が伸びた状態を維持しかつ股関節が曲がっていますね。
ここで一度おさらいです。
下肢の二関節(膝・股関節)を跨ぐ二関節筋には、ハムストリングス
と大腿直筋があります。
ハムストリングスの作用(働き)
→骨盤を後ろに引っ張る(後傾方向)、膝を曲げる、股関節を伸ばす
大腿直筋の作用
→骨盤を前に引っ張る(前傾方向)、膝を伸ばす、股関節を曲げる
となります。
ではこの二関節筋が、具体的な動作においてどのような作用を担って
いると考えられるでしょうか?
そこで次回(こそ)は、
今まで何回かお話ししてきたスクワットという動作を例に、
この二関節筋の働きを考えてみようと思います。

今日も読んでいただき、ありがとうございました。また明日。
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