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Report
1 School of Health Sciences, Deakin University, Burwood, 3125 Victoria, Australia; 2 Department of Integrative Physiology, University of Colorado, Boulder, Colorado 80309
Submitted 22 October 2002; accepted in final form 27 March 2003
The purpose of this study was to quantify the strength of motor-unit coherence from the first dorsal interosseus muscle in young and old adults using data obtained in a previous study, where no differences in motor-unit synchronization between the two groups were observed. The strength of motor-unit coherence was quantified from 47 motor-unit pairs in 11 young adults (age 24.1 ± 4.1 yrs) and from 48 motor-unit pairs in 14 old adults (age 70.4 ± 5.9 yrs). The strength of motor-unit coherence was greater in old adults, particularly at low frequencies of 5–9 Hz (85% greater in old adults at 5 Hz). In addition, the older adults expressed an extra oscillation at approximately 12–13 Hz that was not present in the young subjects. These data demonstrate that common oscillatory inputs to motor neurons (motor-unit coherence) are enhanced in older adults despite no age-related difference in the strength of shared inputs (synchronization). Furthermore, the data emphasize that measures of motor-unit synchronization and coherence highlight different features of the same common input, and a coherence analysis may be a more sensitive tool to characterize shared input to motor neurons.
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