Required force level and isometric tracking

Abstract

An isometric, zero-order (position), one dimensional pursuit tracking task was used to investigated the effects of alterations in the speed of target movement and the control/response ratio (C/R ratio) on human tracking performance. The speed of target movement was varied through different frequency sine-wave forcing functions. The C/R ratio was controlled by varying the force level required to track the target. This required force level was individually tailored I with force levels scaled to the isometric maximum voluntary contraction (MVC) of elbow extension for each subject.

It was hypothesized that higher frequencies of forcing function (5 levels) and higher required force levels (5 levels) would result in degraded tracking performance. The dependent variable investigated was absolute tracking error as a proportion of the required force level for the trial.

Results revealed significant main effects for both Frequency and Force, but not for any of the two- or three-way interactions. The trend was linear for Frequency, with superior tracking occurring at slower frequencies. The effect of Force level was modelled using a second-order polynomial, indicating that superior tracking occurred at the middle required force levels. Regression analysis provided a predicted optimal force level of approximately 65% extension MVC. Subjective mental workload evaluations using the Modified Cooper-Harper scale showed similar results. Results are interpreted with regards to selecting optimum system gains for human manual control.