However, there are other issues to consider if we extrapolate this deduction to mean that the different parts of the abdominal musculature cannot carry out functional activity to different degrees and in different patterns. In this letter, I wish to highlight such issues. Many of the deductions that the upper and lower abs are recruiited in exactly the same manner and to the same degree are based upon surface EMG recordings. Now, one problem with the interpretation of EMGs is that greater potentials measured over any region do not necessarily imply that the muscle locally or over its entire volume is producing 'functional' motor output. For example, it has been found that skilled performers recruit less muscle tissue than less skilled individuals for executing the same activity.
Fatigue can also confound the results.
In this case, a highly trained, strong subject in executing a given abdominal exercise uses a far smaller proportion of his maximal trunk flexion strength than a person who is less strong, so that fatigue even in a single repetition plays a smaller role in the production of EMG or trunk torque. Lest these comments be regarded as somewhat academic, it is interesting to take the analysis out of the laboratory into the folowing few practical and, sometimes most unlikely, situations. Several years ago, one of the TV learning or discovery channels featured a belly dancer in a club who performed an amazing feat of abdominal muscle control. She lay supine on a table with a four coins on either side of her lower abdomen and she contracted her abs sequentially until she had flipped the coins over until they reached the upper abdomen. She then repeated the sequence from top to bottom and then left to right, right to left and then in diagonal sequences.