Background: Loss of muscle strength and fatigue resistance with ageing contribute to frailty, loss of independence, and reduced quality of life. These changes reflect not only muscular decline but also deteriorating communication between the brain and muscles, mediated by the corticospinal tract (CST). Supporting CST function may therefore help maintain mobility and prevent age-related functional decline. Caffeine, one of the most widely consumed dietary compounds globally, is well established to enhance alertness and performance. Acting primarily through adenosine receptor antagonism, caffeine influences both central and peripheral aspects of neuromuscular control. However, its potential to mitigate age-related declines in corticospinal and muscular function remains poorly understood.
Methods: In a randomised, placebo-controlled, crossover, counterbalanced, double-blinded acute study, 20 younger (23.6 ± 2.87y) and 20 older (70.9 ± 5.30y) healthy adults ingested caffeine (3 mg·kg⁻¹) or placebo (maltodextrin). Transcranial magnetic stimulation (TMS) and electromyography (EMG) were used to quantify corticospinal excitability (CSE) via stimulus–response (SR) curves at 3 time points: baseline, post-ingestion (60-minutes), and post-fatigue (120-minutes). Functional measures included elbow flexion and handgrip maximal voluntary contractions (MVCs) and time to fatigue (TTF). Experimental conditions remain blinded as 312 and 794 until analysis is complete.
Results: Condition 312 elicited greater CSE than condition 794 in older adults at post-ingestion and post-fatigue, particularly at mid-range stimulation intensities (State 3; p=0.011; 0.41 ± 0.21 vs 0.31 ± 0.21 mV). This effect was not observed in younger adults (p=0.137; 0.42 ± 0.21 vs 0.39 ± 0.16 mV). Overall, older adults demonstrated lower CSE than younger adults (p= 0.041; 0.46 ± 0.14 vs 0.52 ± 0.14 mV). TTF was significantly longer in condition 312 compared with 794 (p= 0.028; 327 ± 145 vs 287 ± 145 s), with older adults exhibiting greater fatigue resistance than younger adults (386 ± 147 vs 227 ± 91 s), though no age x condition interaction was present (p=0.875). Handgrip MVC revealed a significant age x condition x time interaction (p=0.009), with older adults showing greater post-ingestion strength improvements in condition 312 compared with 794 (186 ± 80 vs 163 ± 72 N).
Discussion and implications: These findings indicate that one experimental condition enhanced both central (CSE) and peripheral (strength and fatigue resistance) aspects of neuromuscular performance, with the most pronounced effects in older adults. The selective increase in CSE in older adults indicates a potential capacity to counteract age-related reductions in central neural drive, possibly by reducing adenosine-related inhibition within motor pathways. Notably, these neurophysiological changes translated to functional improvements relevant to mobility and independence, highlighting the potential of dietary compounds to support healthy ageing and reduce disease risk.
Future direction: Ongoing work will examine spinal excitability and voluntary activation to further localise caffeine’s neuromuscular effects and clarify its role in preserving movement capacity with ageing. By integrating neurophysiological and functional outcomes, this research aims to uncover how everyday dietary factors can be used to both support and study the neural mechanisms underpinning movement and contribute to the prevention of age-related mobility decline.