Electromyographic Analysis of Lower Limb Muscle Activation in Oldest-old Adults with Declined Gait Speed

Background: Declining gait speed in older adults is closely associated with adverse health outcomes, primarily attributed to reduced muscle mass and altered muscle activation patterns. This deterioration is particularly pronounced in the oldest-old (≥80 years). This study aimed to investigate the relationship between lower-limb muscle activation and gait speed in the oldest-old, identifying key muscles influencing gait performance. Methods: Eighty-four community-dwelling adults aged ≥80 years were included. Gait speed was measured using a 4-meter gait speed test, and surface electromyography was used to record muscle activity from the dominant-side rectus femoris, vastus lateralis, vastus medialis, semitendinosus, biceps femoris, gastrocnemius, soleus, and tibialis anterior. Normalized integrated EMG values were calculated to quantify muscle activation intensity. Pearson correlation was used to assess associations between gait speed and muscle activation, followed by multivariate linear regression adjusting for age, sex, and skeletal muscle mass index to identify independent contributors. Results: Pearson correlation analysis revealed significant negative associations between gait speed and the activation of the rectus femoris, vastus medialis, vastus lateralis, biceps femoris, semitendinosus, tibialis anterior, and gastrocnemius. Multiple linear regression identified the rectus femoris, gastrocnemius, and semitendinosus as independent negative factors associated with gait speed, with the rectus femoris showing the strongest association. Age and skeletal muscle mass index were also independently associated with gait speed. Among these factors, age had the greatest influence on gait speed, while muscle activation had a stronger influence than skeletal muscle mass index. Conclusion: Excessive activation of the rectus femoris, gastrocnemius, and semitendinosus muscles independently contributes to gait slowing in the oldest-old. These results demonstrate that neuromuscular activation exerts a stronger influence on gait speed than muscle mass itself, underscoring the imperative for interventions targeting both neuromuscular control and muscle preservation in this population.