Inhibitory signaling as a predictor of leg force control in young and older adults

As the populations of the United States and developed nations age, motor control performance is adversely impacted, resulting in functional impairments that can diminish quality of life. Generally, force control in the lower limb worsens with age, with older adults (OA) displaying more variable and less accurate submaximal forces. Corticospinal inhibitory signaling may influence force control, with those OA who maintain corticospinal inhibitory signaling capacity achieving steadier forces. This study aimed to assess the relationships between lower limb force control and transcranial magnetic stimulation (TMS) measures of corticospinal inhibition (i.e., cortical silent period (cSP) duration and depth). 15 OA and 14 young adults (YA) were recruited for this study. All subjects underwent a TMS protocol to elicit the cSP while maintaining 15% of their maximal force in their knee extensor muscles. OA and YA did not display differences in force control metrics or corticospinal inhibitory measures. However, in OA, maximal cSP depth (%dSP max) was associated with lower force variability. No other significant relationships existed in the YA or OA groups. Future studies will benefit from evaluating a range of target forces and target muscles to assess potential relationships between sensorimotor inhibitory capacity and control of muscle force output.