Development of a device for measurement of multi-directional isometric trunk kinetics in a seated position

Trunk torque is typically quantified in a single plane. This is not ideal since any unmeasured coupled trunk kinetics in other directions, than the intended one, could affect the accuracy and reliability of the strength measurements as well as the ability to corroborate findings with electromyographic recordings. Therefore, an isometric device that simultaneously records trunk kinetics across planes has been developed to aid in the research of trunk control in both the healthy or impaired populations. This device utilizes a six degree-of-freedom load cell and custom designed frame to attach individuals while in the sitting position. The performance of the device was tested in six healthy controls and while using two protocols. The device was able to detect coupled trunk kinetics during maximum lateral flexion and axial twisting torque generation. It also allowed the implementation of a multi-axis isometric protocol showing that subjects were able to generate larger amounts of axial torque during sub-maximal trunk extension compared to sub-maximal trunk flexion. In conclusion, the device and mechanical transformations discussed in this article will aid in the interpretation of multi-directional isometric trunk kinetics in a wide range of populations.