QUANTIFICATION OF TRUNK MUSCLE PERFORMANCE IN STANDING, SEMISTANDING AND SITTING POSTURES IN HEALTHY-MEN

The purpose of this study was to determine trunk muscle performance in the sitting, semistanding, and standing postures during isometric and dynamic extension and flexion movements. Twenty-five male subject vol unteers, with no previous history of back pain participated in the stu dy. A triaxial dynamometer that measures torque, angular position, and velocity was used to measure isometric and dynamic motor output. The dynamometer allows testing in the sitting and standing postures. A cus tom-designed module also allowed testing in the semistanding posture. Each subject was tested in two sessions. The first session included th e physical examination and three trials of isometric maximum voluntary contractions in the three postures. The second session included the d ynamic performance against a resistance equal to 50% of the effort, as measured in the first session. Subjects were instructed to perform fi ve repetitive flexion and extension cycles as fast and accurately as p ossible with maximum effort. An analysis of variance with repeated mea sures design was used to investigate the effects of the postures (stan ding, semistanding and sitting), the direction of exertion (flexion an d extension), and the interaction effects of the isometric and dynamic parameters (maximum and average torque, velocity, power, and range of motion). The effects of direction (F = 98, P< 0.0001) and the interac tion of posture and direction (F = 7.9, P < 0.001) were significant. T he maximum isometric flexion strength was significantly higher in the standing posture than in semistanding and sitting. The maximum isometr ic extension was not affected by the posture (sitting, semistanding an d standing). The average power in standing was twice that of sitting a nd semistanding (P < 0.0001). During dynamic performances, only the ma in effects of posture and direction were significant. There was no dif ference between the semistanding, and sitting postures in terms of the dynamic performances. Maximum torque and velocity in standing were si gnificantly higher than in semistanding, and sitting, which should be considered in the optimization of workplace design.