Reproducibility of intra-abdominal pressure when lifting.

Reproducibility of intra-abdominal pressure (IAP) variation was investigated in fifteen young male subjects when lifting three loads, 49, 98 and 147 N, with three speeds of movement, slow, fast and spontaneous, and starting from four standing postures: trunk erect, trunk forward flexed at 30, 60, and 90 degrees of dorsolumbar inclination. Each lift was replicated five times successively and the whole protocol was replicated at one a week interval. The intra-individual variability in IAP response was assessed using the standard deviation of each series of ten lifts. Results showed that variability of peak IAP increased with the load and with the lifting speed. This effect of speed was especially observed for light loads and in forward bending postures. Trunk posture had in itself no significant effect on IAP reproducibility. However, when the variations in the moment acting at lumbar level were taken into account by considering the IAP to moment ratio, the reproducibility of the response was not affected by the load but only by the trunk posture. Reproducibility was lower in the erect posture than in the three flexed positions. It is suggested that this difference relates to the importance in each posture of the moment acting at the shoulder with respect to the total moment acting at lumbar level.