| Sumario: | Introduction: Sarcopenia is a major risk factor for falls in older adults; however, the neuromuscular characteristics underlying dynamic balance deficits remain poorly understood. Objective: This study aimed to investigate balance performance and relative muscle contribution patterns in older adults with sarcopenia during dynamic limits of stability (LOS) tasks. Methods: Twenty-seven right-dominant older adults with sarcopenia and 27 age-matched non-sarcopenic controls were recruited. LOS tasks were performed using a force platform, while surface electromyography (sEMG) was recorded bilaterally from 10 lower-limb muscles. Amplitude contribution ratio (ACR), load bias ratio (LR), asymmetry index (AI), and Shannon entropy were analyzed. Results: The sarcopenia group exhibited reduced LOS performance across all directions, with greater impairment in the backward direction. LR-left was lower, whereas forward and backward AI values were higher in the sarcopenia group. Repeated-measures analyses revealed significant group effects for LR and AI, without significant direction-related interactions. ACR analysis showed a significant interaction among direction, muscle region, and group. Post hoc analyses indicated increased proximal and decreased distal relative muscle contributions only during the forward task. Shannon entropy was lower in the sarcopenia group. Conclusion: Older adults with sarcopenia exhibited direction-dependent impairments in dynamic balance performance, accompanied by altered proximal-to-distal relative muscle contribution patterns, asymmetric bilateral contribution distribution, and reduced diversity of muscle recruitment patterns. LR, AI, and Shannon entropy may serve as exploratory indices for characterizing relative muscle coordination during dynamic balance tasks and may provide additional insights for the assessment and rehabilitation of sarcopenia-related balance impairments.
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