NoMan
10th July 2001, 08:51
Hmm... it's so hard to find good information on exercise. In in Dr. Michael Yessis's book "Kinesiology of Exercise", it states that EMG studies show there is a difference in electro-chemical stimulation during various ab exercises, and that only the upper abs are used in crunches. This seems strange, as the rectus abdominal muscles are noncontiguously innervated. Researching further, I found this from Dr. Hatfield:
"Electromyographic studies have demonstrated that the upper portion of the recti produced more activity when doing crunches with no weight, but when as little as ten pounds was added, activity was equal throughout the muscle. The same studies demonstrated that reverse crunches can produce greater activity in the lower abs than in the upper abs, but it also produced activity in the obliques. When resistance is applied to the crunch movement, differences in electrical activity disappeared, and contraction became relatively uniform throughout the entire rectus abdominus. So, contrary to popular belief, all abdominal exercises in which substantial resistance (weight) is being overcome will produce equally strong electromyographic activity throughout the entire muscle. In simple terms, no upper or lower part of a muscle is “isolated”.
The only thing that I can figure out from this is that the abdominal muscles abide by the same rule that all muscles do, that they only recruit the amount of fibers necessary to perform a given movement. In the case with the crunches, only a small portion of the muscle fibers were needed for the exercise. Upon adding weight to it, the muscles would require more fibers to produce the same movement, recruiting additional muscle fibers. Of course, "lower ab" exercises shouldn't be ignored, due to the hip flexor involvement. Hmm... more speculation I guess...
"Electromyographic studies have demonstrated that the upper portion of the recti produced more activity when doing crunches with no weight, but when as little as ten pounds was added, activity was equal throughout the muscle. The same studies demonstrated that reverse crunches can produce greater activity in the lower abs than in the upper abs, but it also produced activity in the obliques. When resistance is applied to the crunch movement, differences in electrical activity disappeared, and contraction became relatively uniform throughout the entire rectus abdominus. So, contrary to popular belief, all abdominal exercises in which substantial resistance (weight) is being overcome will produce equally strong electromyographic activity throughout the entire muscle. In simple terms, no upper or lower part of a muscle is “isolated”.
The only thing that I can figure out from this is that the abdominal muscles abide by the same rule that all muscles do, that they only recruit the amount of fibers necessary to perform a given movement. In the case with the crunches, only a small portion of the muscle fibers were needed for the exercise. Upon adding weight to it, the muscles would require more fibers to produce the same movement, recruiting additional muscle fibers. Of course, "lower ab" exercises shouldn't be ignored, due to the hip flexor involvement. Hmm... more speculation I guess...