The effects of age and feedback on isometric knee extensor force control abilities

Objective. To investigate the effects of age and feedback on submaximal isometric force control abilities in the knee extensors. Design. Analysis of a force control task in a quasi-experimental design. Background. The ability to control submaximal strength is important to accomplish activities of daily living. The purpose of this study was to investigate the effects of age, feedback, and force level on force control ability in knee extension, which is often used to accomplish daily activities. Methods. The performance of an isometric force control task was measured in young (mean age 26, SD 2.7 yrs) and older (mean age 72, SD 2.0 yrs) adult healthy male participants. Each participant maintained a steady force in knee extension at two levels of force (20% and 60% MVC) with and without visual bandwidth feedback. Age, force level, and feedback effects were examined on the dependent variables of force variability, bias, and time in bandwidth. Results. Both groups were fairly accurate at accomplishing the task, particularly at the lower force level. The higher force was harder to control, particularly when feedback was absent. The absence of feedback did not affect variability during force control. Older adults performed with less variability and a higher safety margin. Both groups performed better in time spent in bandwidth and safety margin with visual feedback, compared to the no-feedback condition. Conclusions. Healthy older and younger adults performed quite similarly regardless of feedback being provided or not. The intermittent feedback condition may have been more closely aligned with a no feedback condition rather than a continuous feedback condition.