Intra-abdominal pressure during trunk extension motions

Objective. This study was designed to help interpret the biomechanical role of intraabdominal pressure during lifting type motions of the trunk. Design. An in vivo study was performed in which intra-abdominal pressure was observed as subject trunks were subjected to different dynamic trunk loading conditions common during industrial lifting. Background. There is a little consensus as to the biomechanical role of intra-abdominal pressure during lifting, Previous studies have suggested that: it may assist in load relief when lifting, may be involved in trunk stability, and/or may be used as a measure fo spine loading. Thus, in general, our understanding of intra-abdominal pressure is rather poor. Methods. In this study intra-abdominal pressure was monitored using a radio pill in 114 subjects over a series of four experiments. Subject's trunks were subjected to different dynamic trunk symmetric and asymmetric trunk loading conditions that are common during industrial lifting tasks. Results. The results indicated that (1) intra-abdominal pressure increased to significant levels (above 10 mmHg) only when more than 54 Nm of trunk torque were supported; (2) intra-abdominal pressure increases monotonically (up to 150 mmHg) as a function of trunk velocity; and (3) under concentric conditions intra-abdominal pressure increases as a function of greater asymmetry, whereas, under eccentric conditions the response changes to a much lesser extent as asymmetry changes. Conclusions. These findings suggest that intra-abdominal pressure appears to be more a by-product of trunk muscle coactivation. Any mechanical advantage gained from intraabdominal pressure might be in the form of a preparatory action resulting from muscle coactivation that stiffens the trunk just prior to a rapid trunk extension exertion. This function may reinforce previous hypotheses regarding the stability role of intra-abdominal pressure. Relevance Intra-abdominal pressure has been observed during lifting for several decades, yet the biomechanical role of intra-abdominal pressure is poorly understood. This study has attempted to describe how intra-abdominal pressure behaves during lifting motions as the components of lifting are changed. The findings place in doubt biomechanical significance of intra-abdominal pressure. Thus, based upon this study, clinicians need not worry about interpreting intra-abdominal pressure, since it appears to be a by-product of muscle contraction and cocontraction. Copyright (C) 1996 Elsevier Science Ltd.