Lie on your back, put both hands on the abdominal muscles on either side your navel. Raise your head and try to sit up feeling the tension in the rectus abdominis (rectal muscles of the abdomen). You will notice the extreme tightness of these muscles as you slowly sit up. Notice what happens when you finally reach your destination and sit up erect. You are in for a bit of a surprise at this point. The taut muscles of the abdomen after completion of their involuntary movements suddenly become flaccid. Therefore, these abdominal muscles and the muscles on the inner lining (anterior spinal muscles) of the spine perform just one function: namely raising the body from horizontal to the vertical sit-up position and play very little role in maintaining the erect posture. Once the motion is complete their role finishes and some other groups of muscles seem to take over to make you sit erect.

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