Trunk strength in combined motions of rotation and flexion/extension in normal young adults.

Thirty-eight normal healthy young subjects (14 males, 24 females) with mean ages of 23 years (males) and 21 years (females), performed 36 functional rotational tasks of the trunk. The subject's lower extremities were stabilized in a stabilizing platform, allowing the entire motion of flexion-rotation and extension-rotation to take place in the trunk. Of these tasks, 18 were isometric and the other 18 were isokinetic. The isometric tasks consisted of flexion-rotation and extension-rotation from a 20 degrees, 40 degrees and 60 degrees flexed trunk in 20 degrees, 40 degrees and 60 degrees of axial rotation. The isokinetic activity consisted of flexion-rotation and extension-rotation from upright and flexed postures respectively in 20 degrees, 40 degrees and 60 degrees rotation planes at 15 degrees, 30 degrees and 60 degrees/s angular velocities. The results revealed that the males were significantly stronger than females (p < 0.01) and isometric activities produced significantly greater torque compared to isokinetic efforts (p < 0.01). The degree of trunk flexion was not significant; the angle of rotation, although significant, had only a small effect. The 60 degrees trunk rotation was significantly different from 20 degrees and 40 degrees of trunk rotation. The multiple regressions were all significant (p < 0.01); however, they predicted only 40 to 60% of the variations. Based on the results and analysis, it is suggested that the motion involved rather than the torque may have a consequential effect in the precipitation of back injuries.