Electro-myographic study of the abdominal muscles in pregnancy.

Electro-myographic observations were made on abdominal muscles of pregnant individuals under normal and some abnormal conditions at the Ekisaikai Hospital, Kobe. As has been announced by Kawakami (1), these observations preceded his experimental work on the effect of sexual hormones on the muscular activity of the human abdominal muscles. The muscles used were M. obliquus externus et internus. The electrical lead employed was the same type used by Adrian and Bronk. A long Cathelin needle (because of the thick fat layer of the female subjects) was used, into which an enamelled50u copper wire was inserted and properly insulated. The action current from the muscle was passed through an amplifier to a Braun tube or sometimes to a vibrator oscillograph. The subject assumed a standing or lying posture. In the latter instance, the legs were extended or bent upward, but the muscular responses showed no perceptible difference between the two positions of the legs. Following the insertion of the needle into the muscle, there appeared generally a series of discharges, and in nearly all the cases where sustained pains were felt, unusually strong discharges were observed. Such discharges obliterate the true response of the muscle. So in the present observations at least5 minutes were allowed after the cessation of those initial discharges or pains. The abdominal muscles, as remarked by Kawakami (1), show marked regional differences in the electrical response, and therefore, the measurements were performed at the following4points-one10cm. away diagonally upward from the navel and all the others around this point, ,2 cm. away above, below and to the side. (Note the upper portions of the muscles are more likely to be involved in the respiratory movements and show periodic discharges.)