Corticospinal properties following short-term strength training of an intrinsic hand muscle.

Practicing skilled tasks that involve the use of the hand and fingers has been shown to lead to adaptations within the central nervous system (CNS) underpinning improvements in the performance of the acquired task. However, neural adaptations following a period of strength training in the hand is not well understood. In order to determine the neural adaptations to strength training, we compared the effect of isometric strength training of the right first dorsal interosseous (FDI) muscle on the electromyographic (EMG) responses to transcranial magnetic stimulation (TMS) over left M1. The specific aim of the study was to investigate the corticospinal responses, including latency, motor-evoked potential amplitude (MEP), and silent period duration (SP) following 4 week of strength training of the FDI muscle. Sixteen healthy adults (13 male, three female; 24.12±5.21 years), were randomly assigned into a strength training (n=8) or control group (n=8). Corticospinal measures of active motor threshold (AMT), MEP amplitude, and SP duration were obtained using TMS during 5% and 20% of maximal voluntary contraction force (MVC) pre and post 4 week strength training. Following training, MVC force increased by 33.8% (p=.01) in the training group compared to a 13% increase (p=.2) in the untrained group. There were no significant differences in AMT, latency, or MEP amplitude between groups following training. However, in the trained group, there was a 16 ms reduction in SP duration at 5% of MVC (p=.01) and 25 ms reduction in SP duration at 20% of MVC (p=.03). These results demonstrate a task dependent adaptation in corticospinal inhibition via a reduction in cortical SP duration that may in part underpin the strength increases observed following strength training.