Older adults use a unique strategy to lift inertial loads with the elbow flexor muscles

The purpose of this study was to determine the effect of age on the ability to exert steady forces and to perform steady flexion movements with the mu scles that cross the elbow joint. An isometric task required subjects to ex ert a steady force to match a target force that was displayed on a monitor. An anisometric task required subjects to raise and lower inertial loads so that the angular displacement around the elbow joint matched a template di splayed on a monitor. Steadiness was measured as the coefficient of variati on of force and as the normalized standard deviation of wrist acceleration. For the isometric task, steadiness as a function of target force decreased similarly for old adults and young adults. For the anisometric task, stead iness increased as a function of the inertial load and there were significa nt differences caused by age. Old adults were less steady than young adults during both shortening and lengthening contractions with the lightest load s. Furthermore, old adults were least steady when performing lengthening co ntractions. These behaviors appear to be associated with the patterns of mu scle activation. These results suggest that different neural strategies are used to control isometric and anisometric contractions performed with the elbow flexor muscles and that these strategies do not change in parallel wi th advancing age.