BILATERAL INDEX EXPRESSIONS AND IEMG ACTIVITY IN ELDERLY VS. YOUNG ADULTS

Abstract

This study investigated the hypothesis that expressions of bilateral indices (BI) would be higher in elderly compared to young participants. To test this hypothesis, we had 20 older (73.3 ± 4.4) and 21 younger (23.0 ± 0.7) participants perform maximal voluntary isometric contractions (MVC) of the elbow flexor muscles, using the right arm only (RU), left arm only (LU) and both arms simultaneously (R & L BL). These actions were repeated at perceived intensities of 25%, 50%, & 75% MVC. Force data and integrated electromyographical (EMG) activity of the biceps and triceps muscles were collected during each trial. Bilateral index values were calculated [(RBL+LBL)/(RU+LU) × 100–100] for each intensity level in both groups using absolute forces (ABI) and forces normalized to their respective mode (unilateral or bilateral) maximums (MBI). The ABI was parsed into a perceptual component, defined as the MBI, and a physiological component, defined as ABI-MBI. Significant bilateral deficits (p < 0.05), defined as ABI < 0, existed at maximal and submaximal intensities but the submaximal deficits (14–18%) were larger than the maximal deficits (11%). The physiological component of the ABI was 11% at all intensity levels for both groups. There was an inverse relationship between the perceptual component of the ABI and the level of effort. Normalized integrated EMG values were significantly higher (p < 0.05) for unilateral trials than for bilateral trials at all intensity levels. There were no significant differences between the elderly and young participants. Despite the decrease in fast twitch motor units associated with aging, bilateral deficits exist in older adults, are similar to those observed for younger adults, and remain larger for submaximal intensities.