The effects of motion on force control abilities.

Objective: To investigate the effects of motion on submaximal force control abilities in the knee extensors.

Design: Analysis of a force control task in a quasi-experimental design.

Background: Measuring strength control rather than strength capacity may provide insights in therapeutic intervention.

Methods: Twenty younger and 19 older community dwelling healthy adult males were instructed to maintain knee extensor strength at two levels of strength (20% and 60% of the maximal voluntary contraction) within a bandwidth (+/-6.10 N m) with visual feedback in isometric and isokinetic force control conditions. The effects of motion, force level, and age on force control ability were investigated.

Results: The addition of motion to the force control task decreased performance for both groups at both force levels. Isokinetic force control, compared to the isometric, increased force variability at both force levels. In isokinetic force control, as the force level increased, performance decreased for both groups. For the 60% maximal voluntary contraction isokinetic force control task, the older adults, compared to the younger, had an increased bias, increased percent time in bandwidth, and decreased number of correctional instances.

Conclusions: This study has demonstrated that in the presence of motion, healthy younger and older adults experienced a decreased ability to maintain submaximal forces and their ability decreased even further with an increase in force level. Age group differences became more apparent by adding motion and increasing the force level. Further, we have successfully adapted the methodology used to assess isometric force control abilities to isokinetic force control testing in the lower extremities.