Lateral Armrest Support Improves Postural Alignment, Respiratory Mechanics, and Shoulder Muscle Loading During Seated Eating: A Multidimensional Biomechanical Evaluation

Background: Postural collapse and increased reliance on accessory respiratory muscles during meals can compromise ventilatory efficiency, particularly in individuals with respiratory impairment. Anterior elbow-supported sitting is commonly used to unload the upper limbs; however, this posture often induces trunk flexion and cervical extension, which may adversely affect respiratory mechanics. To date, the effects of lateral armrest support on posture and respiratory function during seated eating have not been quantitatively investigated. Objective: To examine the effects of lateral armrest support on thoracic alignment, cervical posture (cervical inclination angle), shoulder muscle stiffness, vital capacity, and subjective comfort during seated eating, compared with unsupported sitting and anterior elbow-supported sitting. Methods: Forty healthy adults completed three randomized sitting conditions: (A) unsupported sitting, (B) anterior elbow-supported sitting, and (C) lateral armrest-supported sitting using a side-mounted armrest. Thoracic kyphosis index, cervical inclination angle, muscle stiffness of the upper trapezius and middle deltoid, vital capacity (VC), and subjective comfort were assessed. Data were analyzed using Friedman tests, with post-hoc pairwise comparisons performed using the Durbin–Conover test with Bonferroni correction. Results: Lateral armrest-supported sitting significantly reduced thoracic kyphosis and upper trapezius muscle stiffness and produced the greatest VC among the three conditions (all p < .01). In contrast, anterior elbow-supported sitting reduced thoracic kyphosis but resulted in significantly smaller cervical inclination angle values, indicating greater cervical extension, compared with the other conditions (p < .001). Subjective comfort ratings were highest in the lateral armrest-supported condition and lowest in the anterior elbow-supported condition. Conclusion: Lateral armrest support provides a biomechanically advantageous seating strategy during eating by improving postural alignment, reducing accessory respiratory muscle loading, and enhancing ventilatory capacity.