Transient effects in corticospinal and reticulospinal tract excitability induced by motor skill and isometric resistance training.

Coordinated movement relies on the proper integration of multiple neural circuits. Motor training can alter the excitability of neural circuits controlling movement, but the pathway-specific effects to the lower limb of motor skill versus isometric resistance training remain unclear. Here, we tested how single 30-minute sessions of cue-paced motor skill and isometric resistance training modulate corticospinal, reticulospinal, and spinal excitability in unimpaired adults (N = 23). Using motor-evoked potentials via transcranial magnetic stimulation, we found motor skill training increased corticospinal excitability, while isometric resistance training did not. In contrast, by assessing reticulospinal tract excitability by StartReact responses and measuring spinal excitability with H/M ratios, F-wave response amplitude, and persistence, we found that each tract's excitability remained largely unchanged. These results suggest that short-term motor skill training selectively enhances corticospinal tract excitability without a measurable impact on spinal or reticulospinal circuits. These results highlight the influence of task complexity on distal lower limb excitability and provide a framework for evaluating neural adaptations across corticospinal, reticulospinal, and spinal circuits.