Bilateral index expressions and iEMG activity in older versus young adults.

Background: This study investigated the hypothesis that expressions of maximal and submaximal bilateral indices would not differ between older and young participants.
Methods: Twenty older (73.3 +/- 4.4 years) and 21 younger (22.4 +/- 0.9 years) participants performed maximal voluntary isometric contractions of the elbow flexor muscles, using the right arm only, left arm only, and both arms simultaneously. The participants were asked to repeat these contractions at what they perceived to be 25%, 50%, and 75% of their maximal voluntary isometric contraction levels.
Results: Significant bilateral deficits (p <.05), defined as a bilateral index <0, existed at maximal and submaximal intensities, but the submaximal deficits (14-18%) were larger than the maximal deficits (11%). Normalized integrated electromyographic values tended to be higher for unilateral trials than for bilateral trials at all submaximal intensity levels. There were no significant differences between the older and young participants.
Conclusions: Despite the decrease in the size of fast twitch motor units associated with aging, bilateral deficits exist in older adults, do not differ from those observed for younger adults, and remain larger for submaximal intensities.