Motor plan differs for young and older adults during similar movements.

Older adults exhibit altered activation of the agonist and antagonist muscles during goal-directed movements compared with young adults. However, it remains unclear whether the differential activation of the antagonistic muscles in older adults results from an impaired motor plan or an altered ability of the muscle to contract. The purpose of this study, therefore, was to determine whether the motor plan differs for young and older adults. Ten young (26.1 ± 4.3 yrs, 4 females) and sixteen older (71.9 ± 6.9 yrs, 9 females) adults participated in the study. Participants performed 100 trials of fast goal directed movements with ankle dorsiflexion while we recorded the EMG activity of the primary agonist (Tibialis Anterior; TA) and antagonist (Soleus; SOL) muscles. From those 100 trials we selected 5 trials in each of 3 movement endpoint categories (Fast, Accurate, and Slow). We investigate age-associated differences in the motor plan by quantifying the individual activity and coordination of the agonist and antagonist muscles. During similar movement endpoints, older adults exhibited similar activation of the agonist (TA) and antagonist (SOL) muscles compared to young adults. In addition, the coordination of the agonist and antagonist muscles (TA and SOL) was different between the two age groups. Specifically, older adults exhibited lower TA-SOL overlap (F_1,23=41.2, P<.001) and greater TA-SOL Peak EMG delay (F_1,25=35.5, P<0.001). This finding suggests that while both age groups displayed similar movement endpoints, they exhibited a different motor plan, as demonstrated by altered coordination between the agonist and antagonist muscles.

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