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Final Program


Final Congress Guide

Specialty Development

900 Section - Relationship Between Trunk Inclination in Sitting and Inspiratory Muscle Strength and Diaphragm Thickening

Wednesday, May 20, 2026
6:00 PM - 7:30 PM PT

    Presenting Author/Autor expositor(s)

  • YF

    Yorimitsu Furukawa, PhD

    Professor
    Tokyo Metropolitan University
    Arakawa, Tokyo, Japan

    • Co-Author/Coautor(s)

  • NS

    Nami Shida, PhD

    Associate Professor
    Tokyo Metropolitan University
    Arakawa-ku, Tokyo, Japan

  • HK

    Hironobu Kuruma, PhD

    Professor
    Tokyo Metropolitan University
    Arakawa-ku, Tokyo, Japan

  • MS

    Mari Sugiyama, MS

    Doctoral Program Student
    Tokyo Metropolitan University
    Arakaw-ku, Tokyo, Japan

Objectives : In seated postures, increased trunk muscle activity for postural control may reduce thoracic compliance and diaphragm mobility, resulting in inefficient respiratory mechanics. Trunk flexion can restrict diaphragmatic descent by decreasing the anteroposterior thoracic diameter and elevating abdominal pressure, whereas slight extension may improve chest wall mobility and the diaphragm length–tension relationship. However, the relationships between trunk angle, inspiratory muscle strength, and diaphragm motion in short sitting remain unclear. To examine how different trunk flexion and extension angles in short sitting affect respiratory function and maximal inspiratory pressure (MIP), and to analyze correlations between MIP and diaphragm thickening ratio.

Design: Thirteen healthy adult females participated (mean age 21.1 years, height 162.5 cm, weight 52.8 kg). Trunk posture was set at 0° (neutral), 10° and 20° flexion, and 10° and 20° extension. Respiratory function and MIP were measured using a respiratory function analyzer (AS-507, Minato Medical Science). Diaphragm thickness and thickening ratio were assessed with a portable ultrasound device (SONON300, Sakai Medical). Trunk angles were measured with a goniometer. Pearson correlations were calculated (p < 0.05).

Results: Mean vital capacity was 3.4 L (%VC: 92.3%). Mean MIP values (cmH₂O) were 29.5 at 0°, 26.2 at 10° flexion, 28.8 at 20° flexion, 30.6 at 10° extension, and 31.8 at 20° extension. Diaphragm thickening ratios were 1.3, 1.1, 1.0, 1.2, and 1.2, respectively. Moderate correlations between MIP and diaphragm thickening ratio were observed at 0° (r = 0.46) and 20° flexion (r = 0.48).

Conclusion:

Trunk flexion tended to reduce both diaphragm thickening and MIP, while slight extension increased MIP with preserved thickening. Moderate correlations in neutral and 20° flexion indicate that diaphragm behavior partly explains inspiratory strength, though chest wall mechanics and accessory muscle activity also contribute. Adjusting trunk alignment in short sitting may therefore help enhance diaphragm-focused training and inspiratory muscle performance.