胸腔足侧运动？难道不是胸腔扩大，不就是吸气吗？

Rectus abdominis, external oblique, internal oblique and transversalis muscles are the most important expiratory muscles, whilst the muscles of the pelvic floor have a supportive role. Contraction of these muscles results in an increase in abdominal pressure, displacing the diaphragm in a cephalad direction. In addition, their insertion into the costal margin results in a caudad movement of the rib cage, assisting expiration by opposing the rib cage muscles. Gastric pressure is a valuable index of their activity because their contraction will always cause an increase in intraabdominal pressure.

腹直肌、腹外斜肌、腹内斜肌和腹横肌是最重要的呼气肌，而盆底肌则起支撑作用。这些肌肉的收缩导致腹压升高，使膈肌向头部方向移动。此外，其止点位于肋缘从而导致胸腔足侧运动，并通过对抗肋间肌来协助呼气。胃内压是衡量这些肌肉活动的有价值的指标，因为这些肌肉的收缩总会引起腹内压升高。

insertion 止点？

caudad movement of the rib cage胸腔向足侧运动？难道不是胸腔扩大，不就是吸气吗？那怎么是呼气肌？