Dual tasking exacerbates force and neural control unsteadiness in sarcopenic older adults

BackgroundSarcopenia 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. Therefore, we investigated whether older adults with sarcopenia exhibit poorer steadiness of force and neural control (i.e., greater motor unit discharge variability, and altered common synaptic input) during submaximal contractions performed under single- and dual-task conditions compared with non-sarcopenic controls and master athletes. MethodsFifty-two older adults were included (74.3{+/-}7.3 years; 50% female). Sarcopenia was defined using Sarcopenia Definitions and Outcomes Consortium criteria based on low grip strength and slow gait speed. Participants (11 with sarcopenia, 22 controls, and 19 masters athletes) performed six sustained isometric ankle dorsiflexion contractions at 30% maximal voluntary torque, three under single-task conditions and three during concurrent serial number subtraction. High-density surface electromyography was recorded from tibialis anterior, and motor unit spike trains were decomposed and tracked across trials. Outcomes included torque coefficient of variation, mean discharge rate, inter-spike interval coefficient of variation, and intramuscular coherence in the delta (1-5 Hz), alpha (5-15 Hz), and beta (15-35 Hz) bands. ResultsSarcopenic individuals had worse torque steadiness (increased torque coefficient of variation) than controls (45-84%) and athletes (39-105%) during single-task, which worsened further (+35% relative to baseline) during dual-tasking. Mean discharge rates (proxy of neural drive) slightly increased during dual-tasking in all groups by [~]2.6%, with no between-group differences. Discharge rates coefficient of variation (Proxy of neural control unsteadiness) increased 5.5% in sarcopenia, was unchanged in controls, and decreased 4.1% in athletes during dual-tasking. Delta-band coherence decreased 5.5% during dual-tasking across all groups. Alpha-band coherence increased only in sarcopenia during dual-tasking (20.6%). Beta-band coherence increased 20.6% in sarcopenia but decreased 3.6% in controls and 3.8% in athletes during dual-tasking. ConclusionsOlder 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 an increase in physiological involuntary tremor-related oscillations (alpha band), which contribute to greater force unsteadiness. 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 to reduce mobility impairment and fall risk. These findings support expanding muscle-centric views of sarcopenia to include neural mechanisms of motor control.