Determining the cortical, corticospinal, and reticulospinal responses to metronome-paced and self-paced strength training.

Purpose: The acute neurophysiological responses to resistance training (RT), particularly in corticospinal and reticulospinal pathways, remain unclear. This study investigated the effects of different RT modalities on these pathways. Methods: Thirty-six RT-naive participants (10 males, 2 females per group) were randomly assigned to metronome-paced RT (MP-RT), self-paced RT (SP-RT), or a control group. Cortical, corticospinal, and cortico-reticulospinal responses were assessed using transcranial magnetic stimulation (TMS), while reticulospinal tract (RST) excitability was evaluated by examining the effect of startle stimulus on rate of force development (RFD) at baseline, 5 min, and 30 min post-exercise. Results: MP-RT enhanced corticospinal excitability by 50% at 5 min (p = 0.017) and 72% at 30 min (p < 0.001). MP-RT reduced short-interval cortical inhibition (SICI) by 56% and cSP by 12% at 5 min and ~ 20% at 30 min. SP-RT reduced cSP by 17% at 5 min at 150% active motor threshold (AMT; p < 0.05). At 170% AMT, cSP reductions were observed in both MP-RT (23%) and SP-RT (18.9%; p < 0.001). SP-RT increased ipsilateral to contralateral motor evoked potential amplitude ratio (ICAR) by 48% at 30 min (p < 0.001), and RFD during the initial 50 ms under startling stimuli by 60% at 30 min (p = 0.039). Conclusion: MP-RT enhances intracortical/corticospinal excitability and may support rehabilitation from corticospinal injury/impairment, while SP-RT improves cortico-reticular and reticulospinal excitability, making it suitable for athletes or older adults seeking improved gross strength.