Components The levator ani muscle consists of pubococcygeus, iliococcygeus and coccygeus. The puborectalis muscle was discovered in 1897, which was considered as the medial portion of the pubococcygeus and also one of the components of the levator ani muscle by most of the investigators [7]. Unlike others, in 1980, XXXX suggested that the puborectalis muscle was not one of the components of the levator ani muscle based on anatomic observation [8]. In 2007, XXXX et al approved XXXX’s viewpoint by MRI and also verified that the puborectalis muscle and the levator ani muscle were a pair of antagonistic muscles using CT defecography [3,4].
Portions In 1979, XXXX divided the levator ani muscle into two functional portions, the transverse portion and the vertical portion. He also though that the longitudinal rectal muscle (smooth muscle), the vertical portion of the levator ani muscle (striated muscle) and the inferior extended portion of the puborectalis muscle (striated muscle) composed the conjoined longitudinal muscle[9]. However, subsequent histological researches approved that there was no striated muscle fiber in the conjoined longitudinal muscle [10]. In addition, a inner-anus MRI study with 100 cases and several other MRI studies only confirmed the presence of the transverse portion [11, 12]. Thus, in 2005, the 39th edition of Gray’s Anatomy accepted the “truth” that there is no vertical portion in the levator ani muscle [13]. Unlike others, in 2007, XXXX et al confirmed that the levator ani muscle had not only a transverse portion but also a vertical portion with function of opening the anus when they made special researches on the imaging anatomical physiology of the levator ani muscle [3, 4]. In 2009, XXXX et al continued to research the vertical portion and found that it possibly changed into more than 20 chordae tendineae (collagen fiber). They also found that the puborectalis muscle did not have the inferior extended portion. This result could explain why there was no striped muscle-fiber in the conjoined longitudinal muscle and improved the understanding of the levator ani muscle. XXXX et al thought that a complete levator ani muscle consisted of tendinous arch, muscle belly, anococcygeal raphe and chordae tendineae. Meanwhile, the reason of the error in inner anus MRI research has been found. Inner-anus coils twisted the transverse portion and the vertical portion, which made previous investigators misunderstand the vertical portion as the longitudinal rectal muscle or other muscles [6].
Mode of constriction There are three hypotheses. In 1979, XXXX thought that the levator ani muscle was stimulated by intra-abdominal pressure during defecation. It was shortened due to isotonic contraction, and then the pelvic floor was elevated. In 1995, XXXX et al thought that central nerve system inhibited the levator ani muscle during defecation. The levator ani muscle was relaxed in coordination with other pelvic muscles in order to descend the pelvic floor. In 1997, XXXX concluded that isometric contraction occurred in the levator ani muscle after being stimulated by intra-abdominal pressure during defecation. The descending of pelvic floor was caused by both its tension and intra-abdominal pressure. In CT defecography, it showed that the levator ani muscle was not shortened during defecation. The electromyogram research approved that the myoelectrical activities in the levator ani muscle were enhanced along with the increasing of intra-abdominal pressure. Above findings showed that shortened isotonic contraction did not occur in the levator ani muscle and there was no relax during defecation, which potentially supported a third hypothesis, namely isometric contraction [4]. If cancer had invaded into the levator ani muscle, in which shortened isotonic contraction occurred, the partly resected portion of the muscle must be repaired and replaced by muscles which could be optionally shortened. This is difficult and irrealizable at present. The isometric contraction in the levator ani muscle suggested that the resected portion of the levator ani muscle could be repaired and replaced by fascia tissue or biological mesh, which had no function of shortening. This means that reconstruction of pelvic floor is comparatively easier.
Function and name In 1555, XXXX named “the anus-elevating muscle”. In 1847, XXXX changed the name of “the anus-elevating muscle” to the levator ani muscle, which had been continuously used to this day [7]. In 1997, XXXX proposed that the puborectalis muscle actually played the role of lifting the anus instead of the levator ani muscle according to defecography. In 2007, XXXX confirmed above hypotheses by CT defecography [4]. Since the actual functions of the levator ani muscle are to descend the anus and pelvis, open the urogenital hiatus and anus, the levator ani muscle is really an anus-descending muscle or a pelvis-descending muscle. This new anatomical physiological sign of anus descending in the levator ani muscle overturned the concept of anus elevating, which has existed for 450 years. Furthermore, the key point of current pelvic floor muscle function theory has also been overturned, which indicates that the mechanism of defecation, urination and childbirth need to be thoroughly modified.

组成 提肛肌由耻尾肌、髂尾肌和尾骨肌3个肌肉组成。耻骨直肠肌发现于1897年，多数学者视其为耻尾肌的内侧部，即提肛肌的一部分[7]；与众不同，1980年XXXX依据解剖学观察，提出了耻骨直肠肌不是提肛肌的组成部分[8]。2007年XXXX等用MRI证实了XXXX的这一观点，并用CT排便造影证实了耻骨直肠肌与提肛肌是一对拮抗肌[3, 4]。
分部 1979年XXXX将提肛肌分为横行部和垂直部2个功能部，并认为直肠纵肌（平滑肌）、提肛肌垂直部（横纹肌）和耻骨直肠肌下延部（横纹肌）共同构成了联合纵肌[9]。然而，其后的组织学研究证实联合纵肌并无横纹肌纤维[10]，此外一组100例肛内MRI研究和多组MRI研究只确认了横行部的存在[11, 12]；所以2005年的格氏解剖第39版接受了提肛肌没有垂直部这一“事实” [13]。 与众不同，2007年XXXX等在专门研究提肛肌的影像解剖生理时确认，提肛肌不仅有横行部，而且有垂直部，并且显示了垂直部的开肛作用[3, 4]。2009年XXXX等继续研究了垂直部，发现垂直部可能变成了20余个腱索（胶原纤维），还发现耻骨直肠肌并无下延部；此结果合理地解释了联合纵肌无横纹肌纤维，也增进了对提肛肌认识；XXXX等认为完整的提肛肌是由腱弓、肌腹、肛尾缝和腱索构成的。与此同时，肛内MRI研究出错的原因也被找到，主要原因是肛内线圈扭曲了横行部和垂直部的延续关系，使得以往的研究者误将垂直部看做直肠纵肌或别的肌肉[6]。
收缩方式 有3种猜想。1979年XXXX认为排便时腹内压刺激提肛肌使其发生缩短的等张收缩，使盆底上升；1995年XXXX等人认为排便时中枢神经系统抑制提肛肌使其与其它盆底肌协同放松，以便盆底下降；1997年XXXX认为排便时腹内压刺激提肛肌使其做等长收缩，其张力和腹内压共同使盆底下降；CT排便造影显示排便时提肛肌并不缩短，肌电图研究证实提肛肌的肌电活动会随着腹内压的升高而增强；这说明排便时提肛肌没有执行缩短的等张收缩，也不可能是放松，故而倾向于支持第3种猜想，即等长收缩[4]。如果提肛肌执行缩短的等张收缩，一旦肿瘤侵犯了提肛肌并被部分切除，那么切除部分就必须用可以随意缩短的肌肉来修复，这是困难的，也是目前不能实现的。提肛肌做等长收缩，暗示提肛肌的切除部位可用无缩短功能的筋膜组织或生物补片等加以修补，这意味着盆底重建将变得比较容易。
功能与名称1555年XXXX命名了举肛肌，1847年XXXX将举肛肌更名为提肛肌，后者被沿用至今[7]。1997年XXXX依据X线排便造影所见，提出提肛肌不提肛，耻骨直肠肌才是真正的提肛者等猜想；2007年XXXX等采用CT排便造影证明了上述猜想[4]。由于提肛肌的真正作用是降肛、降盆、开泌尿生殖裂孔和开肛，因此提肛肌实为降肛肌或降盆肌。提肛肌降肛这一新解剖生理学现象，颠覆了450年以来的提肛观念，进而颠覆了现行盆底肌功能理论的理论核心，表明排便、排尿和分娩机理需要做重大修改。