Acute corticospinal and reticulospinal responses to strength training in ageing

Ageing is associated with declines in neuromuscular function, yet the neural mechanisms underlying strength adaptations in older adults remain unclear. While the corticospinal tract (CST) is the primary pathway for voluntary movement, the reticulospinal tract (RST) may play a compensatory role with age. This study investigated CST and RST responses following a single session of high-intensity metronome-paced strength training (MPST) in young and older adults. Thirty-five participants (17 young, 18 older) performed unilateral biceps curls at 70-75 % of their one-repetition maximum (1-RM). Cortical and subcortical excitability were assessed pre- and post-exercise using transcranial magnetic stimulation (TMS) and the StartReact paradigm. Young adults showed significant increases in corticospinal excitability (CSE; p < 0.05) and early-phase motor evoked potentials (MEPs) following exercise, whereas no changes were observed in older adults. Both groups exhibited reductions in silent period duration (SP; p < 0.01) and short-interval intracortical inhibition (SICI; p < 0.05), suggesting a general release of inhibition. However, no significant changes in reaction time or evidence of enhanced RST drive were observed in either group. These findings highlight age-related differences in the modulation of descending pathways, with older adults showing reduced CSE plasticity following acute MPST, possibly reflecting delayed potentiation due to ageing. Although MPST effectively reduced inhibition, it may be insufficient to engage the RST in older adults. Future research should explore alternative training modalities that more directly target subcortical circuits to optimise functional outcomes in ageing populations.