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Lateral armrest support improves postural alignment, respiratory mechanics, and shoulder girdle loading during seated
Daisuke Tashiro1, Kaito Tou2, Ikoi Okano3
1Department of Occupational Therapy, Faculty of Rehabilitation, Kobe Gakuin University, 518 Arise Ikawadanichou, Nishi-ku, Kobe, Hyogo, 651-2180, Japan. tashiro@reha.kobegakuin.ac.jp.
Background:
Postural collapse and increased reliance on accessory respiratory muscles during meals can compromise ventilatory efficiency, particularly in individuals with respiratory impairment. Forward 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 (upper trapezius and middle deltoid), vital capacity, and subjective comfort during seated eating in healthy young adults, compared with unsupported sitting and anterior elbow-supported sitting.
Methods:
Forty healthy young 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:
Thoracic kyphosis index differed significantly across conditions (p = .002), with both forward elbow-supported and lateral armrest-supported sitting showing lower values than unsupported sitting. Cervical inclination angle also differed significantly (p < .001), with forward elbow-supported sitting demonstrating greater cervical extension than the other conditions. Upper trapezius muscle stiffness was significantly reduced in the lateral armrest-supported condition compared with unsupported and forward elbow-supported sitting (both p < .01). Vital capacity was significantly greater in the lateral armrest-supported condition than in unsupported sitting (p = .003). Subjective comfort ratings were highest in the lateral armrest-supported condition (p < .001).
Conclusion:
Lateral armrest support demonstrated biomechanical advantages in healthy young adults, including improved spinal alignment, reduced shoulder girdle loading, and greater vital capacity compared with unsupported sitting. These findings provide preliminary mechanistic insight and may inform future investigations in clinical populations; however, direct extrapolation to individuals with respiratory or neurological impairment requires further study.
