Abstract
{\it Purpose:} The purpose of this study was to assess the effect of varying the measurement axis of the subject relative to an isokinetic dynamometer on the peak flexion and extension moment of the trunk. The effect of testing position (sitting or standing) on peak moment was also investigated.{\it Methods:} Thirty healthy young subjects [8 male, 22 female] were selected at random from a pool of 90 volunteers and asked to perform concentric sagittal flexion-extension cycles at velocities of 60 deg/s, 120 deg/s and 180 deg/s in both the seated and standing position with respect to 5 measurement axes. The subjects were initially aligned with the highest point on the iliac crest(reference axis) and then aligned with 4 measurement axes displaced from the reference axis (25∼mm anterior/posterior and 50mm superior/inferior). {\it Results:} Two-way repeated measures ANOVA revealed significant differences($\alpha < 0.05$) between peak moments recorded between axes and velocity for flexion and extension, however no difference with respect to testing position, i.e., sitting versus standing. Post hoc multiple comparison tests by the Scheff?method revealed that all measurement axes tested were statistically different [$P < 0.001$] from the reference axis, however there were no differences between the two inferior axes [$P = 0.999$] and the two superior axes [$P = 0.982$]. The inferior measurement axes consistently produced greater peak moments than the reference axis while the superior axes consistently produced lower peak moments than the reference axis. Males produced significantly greater peak moments than did females [$P = 0.000$]. {\it Conclusions:} Measurement axis alignment significantly effects the peak moment recorded. Furthermore, these results reinforce the need for accurate and consistent alignment between the subject and the dynamometer. The position of the subject [seated/standing] did not significantly affect the measured peak moment when using the Lido Active Back System in this study.