ISOMETRIC MAXIMAL AND SUBMAXIMAL TRUNK EXTENSION AT DIFFERENT FLEXED POSITIONS IN STANDING - TRIAXIAL TORQUE OUTPUT AND EMG

Thirty-one healthy men were tested for the effects of trunk-flexion po sitions (0-degrees, 15-degrees, and 35-degrees) in standing on triaxia l torques and electromyogram of 10 trunk muscles during voluntary maxi mal and submaximal isometric trunk extension. At a more flexed positio n, both erector spinae and latissimus dorsi showed significantly highe r RMS-EMG. The abdominal obliques were coactivated only during 100% ma ximum voluntary exertion at each posture. In all tests, the rectus abd omini were quiet. Mean maximum extension torque increased significantl y at 15-degrees and 35-degrees of trunk flexion. The ratio of extensio n torque over RMS-EMG of the trunk extensor muscles, called the neurom uscular efficiency ratio (NMER), also increased in the more flexed pos ture. However, NMER has to be interpreted with caution because it is a ffected both by posture and exertion levels. The effects of posture on the torque generation capability of the trunk question the validity o f the current lifting recommendations.