We have developed a device (Twister) to study the regulation of tonic muscle activity during active postural maintenance. Twister measures torsional resistance and muscular responses in standing subjects during twisting of the body axis. The device can be flexibly configured to study various aspects of tonic control across the neck, trunk, and/or hips.
Gurfinkel, V. S., Cacciatore, T. W., Cordo, P. J., Horak, F. B. Method to Measure Tone of Axial and Proximal Muscle. J. Vis. Exp. (58), e3677, doi:10.3791/3677 (2011).