RESPONSES OF INTRAABDOMINAL PRESSURE AND ABDOMINAL MUSCLE-ACTIVITY DURING DYNAMIC TRUNK LOADING IN MAN

The purpose of this study was to determine and compare interactions be tween the abdominal musculature and intra-abdominal pressure (IAP) dur ing controlled dynamic and static trunk muscle loading. Myoelectric ac tivity was recorded in six subjects from the rectus abdominis, obliquu s externus, obliquus internus, transversus abdominis and erector spina e muscles using surface and intra-muscular fine-wire electrodes. The I AP was recorded intra-gastrically. Trunk flexions and extensions were performed lying on one side on a swivel table. An adjustable brake pro vided different friction loading conditions, while adding weights to a n unbraked swivel table afforded various levels of inertial loading. D uring trunk extensions at all friction loads, IAP was elevated (1.8-7. 2 kPa) with concomitant activity in transversus abdominis and obliquus internus muscles-little or no activity was seen from rectus abdominis and obliquus externus muscles. For inertia loading during trunk exten sion, IAP levels were somewhat lower (1.8-5.6 kPa) and displayed a sec ond peak when abdominal muscle activity occurred in the course of dece lerating the movement. For single trunk flexions with friction loading , IAP was higher than that seen in extension conditions and increased with added resistance. For inertial loading during trunk flexion, IAP showed two peaks, the larger first peak matched peak forward accelerat ion and general abdominal muscle activation, while the second correspo nded to peak deceleration and was accompanied by activity in transvers us abdominis and erector spinae muscles. It was apparent that differen t loading strategies produced markedly different patterns of response in both trunk musculature and intra-abdominal pressure.