Relationship Between the Mobility Method and Limb Skeletal Muscle Morphology in the Institutionalized Elderly in Japan: A Study Using Ultrasound Imaging to Evaluate Skeletal Muscle Structure

Background Reduced mobility among institutionalized elderly individuals is associated with an increased risk of falls, progression to dependence on nursing care, and decline in activities of daily living. However, the qualitative changes in skeletal muscle structure in this population remain poorly understood. This study aimed to noninvasively evaluate muscle morphology, including muscle fiber alignment, as a potential early marker of functional decline. Methods This cross-sectional study included 41 elderly residents (mean age, 85.7 ± 8.7 years) of a long-term care facility. Participants were classified into four groups according to their primary means of mobility: independent walking/cane, walker, wheelchair, and stretcher/bed-bound. Physical function was assessed using grip strength, limb circumference, and the Barthel Index. Ultrasound imaging was used to evaluate the muscle thickness, subcutaneous tissue thickness, and myofiber alignment in the upper arm, forearm, thigh, and lower leg. Group comparisons were analyzed using one-way analysis of variance, or Kruskal-Wallis tests with post hoc analysis, as appropriate. Results Participants with higher mobility showed significantly greater muscle thickness, grip strength, limb circumference, and Barthel Index scores, along with clear myofiber alignment. In contrast, those with lower mobility exhibited obscured alignment. The lowest-mobility group also demonstrated relatively thicker subcutaneous tissue in the upper arm and forearm. Conclusions Maintenance of mobility in institutionalized elderly individuals is associated with both quantitative and qualitative preservation of skeletal muscle. Ultrasound assessment of muscle fiber alignment and subcutaneous tissue thickness may serve as a useful early indicator of sarcopenia, supporting timely preventive interventions.