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Yoga shoptalk, June, 2003

Yoga shoptalk, June, 2003

I’ve done thousands of leglifts and crunches over the years, but I am still confused about the respective roles of the hip flexors and superficial abdominal muscles in those exercises. Please explain.

Answer:

You are not alone. This is an important and frequently misunderstood subject, and I have treated it once before in this website-in the Yoga Shoptalk of September, 2002 (see archives). After reading the following explanation, I suggest that you make a careful study of that earlier discussion, as it explores additional subtleties.

First, an aside: I notice that you asked about “superficial” abdominal muscles, which tells me that you must possess the first printing of Anatomy of Hatha Yoga (identifiable by black text only on the back cover, as contrasted with red, green, blue, and black text on the back covers of later printings). To clarify: The phrase “abdominal muscles” was everywhere substituted for the phrase “superficial abdominal muscles” in all printings subsequent to the first. The historical perspective for this change is as follows. Teaching students without a biomedical background, I generally found that they had a great deal of difficulty comprehending the anatomy, disposition, and functions of the hip flexors (that is, the psoas and iliacus muscles) without seeing a cadaver, mainly because these muscles are hidden in the pelvis, in contrast, for example, to the biceps and triceps brachii, which are apparent on the surface of the body and are thus easily envisioned. So I hit on the idea of explaining that the hip flexors can be thought of as “deep” abdominal muscles since they are located deep in the abdominopelvic cavity and are visible only after the abdominal and pelvic organs are removed, and that seemed to help novices understand. I then naturally fell into referring to the abdominal muscles proper (rectus abdominis, external and internal abdominal obliques, and transversus abdominis) as "superficial" abdominal muscles. In showing early drafts of the manuscript to biomedical experts, however, I was told emphatically that the idea of hip flexors as deep abdominal muscles was contrary to established usage and therefore ill-advised. I agreed, and obediently deleted all references to deep abdominal muscles from the working manuscript, thinking that it would still be useful to refer to abdominal muscles generally as superficial abdominal muscles. It was not enough. As professionals looked at the result in the first printing, I got a small but steady stream of criticism for referring to "superficial" abdominal muscles, so for all later printings, I deleted the word "superficial" throughout the text and illustrations everywhere that term was used in reference to abdominal muscles.

And coming back to your question: The short answer is that leglifts (hip flexions or thigh flexions, technically, but that’s too cumbersome to say, and everyone knows that leglifts are carried out at the hip joint since no one can hyperextend the knees significantly) are mainly accomplished by the hip flexors, that is the iliacus and psoas muscles, and that crunches are mainly accomplished by the abdominal muscles, especially the rectus abdominis muscles.

The long answers are more complex. First, the iliacus muscles act rather differently from the psoas muscles in doing leglifts. They both terminate on the femur in the upper thigh, and thus flex the thigh, but the iliacus muscle takes origin from the inner surface of the ilium on each side, and the psoas muscles take origin from the front of the lumbar spine. The actions of the iliacus and psoas muscles do complement one another, however, because the sacrum and lumbar spine are closely connected to the ilia. During leglifts the psoas muscles bypass as it were the pelvis and yet place strain on the iliolumbar and sacroiliac ligaments (the lumbar spine and sacrum being intimately connected to the ilia at the sacroiliac joints), and the iliacus muscles create tension indirectly in the torso and lower spine for the same reason. The need and rationale for using the abdominal muscles for bracing the lower back against the floor during double leglifts (and thus acting as synergists for double leglifts) is too complex to reiterate here but is extremely important and is explored in detail in chapter 3 of Anatomy of Hatha Yoga (Don’t forget, since the abdominal muscles do not attach in any way to the femurs, they have no direct effects on leglifts.)

The abdominal muscles, especially the rectus abdominis muscles, are prime movers for doing abdominal crunches. But the other abdominal muscles, which include the external and internal abdominal obliques and transversus abdominis muscles, are also important, since the combination of all of these plus the recti abdomini in the body wall create an hydraulic tube to protect the spine and intervertebral disks, another topic which is discussed in detail in chapter 3. Although neither the iliacus or the psoas muscles are prime movers for crunches, they do act as synergists in bracing the pelvis when the hips are partially flexed in a standard position for crunches, as is shown in figure 3.1 in Anatomy of Hatha Yoga. Other synergists for both crunches and leglifts, usually overlooked, are the muscles of respiration (especially the respiratory diaphragm) and the pelvic diaphragm. Without a strong respiratory diaphragm, you would have to hold your breath at the glottis during both leglifts and abdominal crunches, which is undesirable for many reasons, and without a strong pelvic diaphragm and its associated urinary and anal sphincters, you would be incontinent.