A triaxial dynamometer to monitor lateral bending and axial rotation moments during static trunk extension efforts

Objective. The purpose of the study was to describe a new static triaxial d ynamometer designed to monitor the lateral bending and axial rotation momen ts during trunk extension efforts. Background. Most studies on back muscle function using electromyographic sp ectral analysis have not controlled moments produced about the three orthop aedic axes during trunk extension efforts. Criteria to control lateral bend ing and axial rotation moments during extension efforts have not been propo sed in the literature. Methods. Fourteen healthy subjects performed three trunk extension ramp con tractions (0-100% of the maximal voluntary contraction). Triaxial L5/S1 mom ents at 20%, 40%, 60% and 80% of the maximal voluntary contraction in exten sion were extracted.' Results. During the extension efforts, the lateral bending and axial rotati on moments at L5/S1 increased significantly across the force levels and rea ched 6.2 Nm (SD: 6.6) and 6.1 Nm (SD: 4.5), respectively, at 80% of the max imal voluntary contraction. Tolerance limits were proposed to control these associated efforts in the context of the electromyograghic' analysis of ba ck muscles. Relevance Simultaneous measurement of lateral bending and axial rotation mo ments at L5/S1 during extension efforts might help to explain and control l oad sharing between back muscles during extension efforts. (C) 2001 Elsevie r Science Ltd. All rights reserved.