Dual-Tasking Exacerbates Force and Neural Control Unsteadiness in Older Adults With Sarcopenia.

<h4>Background</h4>Sarcopenia is associated with impaired physical function. Dual-task conditions, which increase cognitive demand during motor performance, may reveal deficits in neuromuscular control that are not evident during isolated motor tasks. We investigated whether older adults with sarcopenia exhibit poorer force and neural control (i.e., greater force and motor unit inter-spike variability and altered common synaptic input) during single- and dual-task conditions compared with non-sarcopenic controls and masters athletes.<h4>Methods</h4>Sarcopenia was defined using Sarcopenia Definitions and Outcomes Consortium criteria (low grip strength and slow gait). Participants (11 sarcopenic, 22 controls and 19 masters athletes; 74.3 ± 7.3 years; 50% female) performed sustained isometric ankle dorsiflexion contractions at 30% of maximal voluntary torque, without (single-task) and with concurrent serial number subtraction (dual-task). Motor unit spike trains were decomposed from high-density surface electromyograms. Outcomes included torque and inter-spike interval coefficient of variation (index of discharge regularity linked to torque steadiness) and intramuscular coherence: delta (1-5 Hz; low-frequency common input related to force fluctuations), alpha (5-15 Hz; which may include tremor-related, spinal and afferent contributions) and beta (15-35 Hz; commonly associated with corticospinal input) bands.<h4>Results</h4>Individuals with sarcopenia had higher torque coefficient of variation (worse steadiness) than controls in single- and dual-task by 45% and 84% and athletes by 39% and 105%, respectively. In individuals with sarcopenia, coefficient of variation rose ~35% from single- to dual-task. Mean discharge rate (a proxy of neural drive) increased ~2.6% during dual-tasking in all groups, without between-group differences. Inter-spike interval coefficient of variation increased by 5.5% in sarcopenic, was unchanged in controls and decreased 4.1% in athletes. Delta-band coherence decreased 5.5% across all groups, whereas alpha-band coherence increased in sarcopenic only (20.6%). Beta-band coherence increased 14.5% in sarcopenic but decreased 8.4% in controls and 13.3% in athletes.<h4>Conclusions</h4>Older adults with sarcopenia exhibit poorer force and neural control steadiness, and both deficits worsen under cognitive load. These changes are accompanied by alterations in common synaptic input, particularly increases in alpha and beta bands in individuals with sarcopenia, likely contributing to their greater force unsteadiness during dual-tasking. Neural control unsteadiness during dual-task performance may therefore represent a neural feature of sarcopenia-related functional impairment. Assessing neuromuscular control during cognitively demanding tasks may improve detection of neural dysfunction and identify mechanistic targets for interventions aimed at preserving mobility in older adults. These findings support expanding muscle-centric views of sarcopenia to include neural mechanisms of motor control.