Agonist-antagonist Coactivation Differs for Young and Old Adults During a Maximal Voluntary Contraction

Abstract

Older adults often exhibit altered agonist-antagonist activity compared with young adults during maximal contractions (MVCs), however, the modulation of agonist-antagonist coactivation has not been determined. PURPOSE: To determine whether the agonist-antagonist EMG coherence differs between young and old adults during MVCs. METHODS: Seventeen young subjects (24±5 yrs) and 16 old subjects (71±7yrs) performed six abduction MVCs with the first dorsal interosseus muscle of the left (non-dominant) index finger. For the MVC task, subjects were instructed to produce the maximal force in the briefest time possible and to maintain the maximal force for 2 s. The EMG activity of the single agonist (first dorsal interosseus; FDI) and single antagonist (second palmar interosseus; SPI) muscles was recorded with intramuscular electrodes. Coherence analysis was performed on the interference EMG signals of the FDI and SPI muscles during each MVC trial. Maximal coherence was quantified for six frequency bands: 0–3.9 (delta), 4–7.9 (theta), 8–12.9 (alpha), 13–34.9 (beta), 35–59.9 (low gamma), and 60–100 Hz (high gamma). RESULTS: The maximal abduction force was not significantly different (P = 0.129) for the young (24.3 ± 7.2 N) and old (26.9 ± 14.3 N) subjects. Despite the similar peak abduction force for the two groups of subjects, the peak agonist-antagonist coherence resided in different frequency bands. Although both young (0.12 ± 0.11) and old (0.10 ± 0.09) adults exhibited significant peaks in the low-gamma band (35–59.9 Hz) of the coherence spectrum, the peak in the theta band (4–7.9 Hz) was greater for the old subjects compared with young subjects (0.13 ±0.10 vs. 0.07 ± 0.10; P <0.001). CONCLUSIONS: These findings suggest that the common oscillatory input to the agonist and antagonist muscles during a maximal voluntary contraction with the first dorsal interosseus muscle differs for young and old adults. Supported by NIA awards R03 AG024662 (EAC) and R01 AG09000 (RME).