The purpose of the study was to determine the practice-induced adjustments in the motor-output variability and the agonist-antagonist activity that accompanied improvements in end-point accuracy of goal-directed isometric contractions in young and old adults. Young and old adults performed 100 trials that involved accurately matching the peak of a force trajectory (25% maximum) to a target force in 150 ms. End-point accuracy was quantified as the absolute difference between the target and the peak force and time to peak force. Motor-output variability was expressed as the SDs of the force trajectory, peak force, and time to peak force. The force and time errors differed between the two groups initially, but after 35 practice trials the errors were similar for the two groups. Reductions in force end-point error were predicted by decreases in the variability of the force trajectory for both groups, adaptations in the agonist (first dorsal interosseus) and antagonist (second palmar interosseus) EMG for young adults, and adaptations only for the agonist EMG for old adults. Reductions in time end-point error were predicted by increases in the SD of time to peak force and a longer delay to the peak EMG of the antagonist muscle for young adults, but by decreases in the SDs of time to peak force and force trajectory and a shorter delay to the peak EMG of the antagonist muscle for the old adults. The findings indicate that the neural adjustments underlying the improvement in end-point accuracy with practice differed for young and old adults.