Association between diaphragm excursion and whole-body muscle mass in older adults: an observational study.

Symptoms of diaphragm dysfunction, such as exertional dyspnea and decreased exercise tolerance, share similarities with the symptoms of skeletal muscle mass reduction caused by conditions like sarcopenia. Given that the diaphragm is also a skeletal muscle, sarcopenia may be associated with diaphragm dysfunction, but the specifics of this relationship remain unclear. This study aimed to assess the relationship between diaphragm function-measured by ultrasonography (thickness, thickening fraction, and excursion)-and muscle mass of the extremities, trunk, and whole body using bioimpedance analysis. We recruited older adults from an outpatient clinic for swallowing rehabilitation or frailty. Muscle mass was measured through bioimpedance analysis, and diaphragm function was evaluated with ultrasonography. The relationships between diaphragm ultrasound results and muscle mass measurements were analyzed with regression models adjusted for age, sex, and height. The study included 114 participants (mean age 78.0 years; 45.6% male). The skeletal muscle index was 7.2 kg/m² for men and 5.9 kg/m² for women, with 20% meeting the Asian Working Group for Sarcopenia 2019 criteria. Diaphragm excursion during deep breathing was significantly associated with muscle mass of the extremities, trunk, and whole body (p < 0.001 in simple analysis; p < 0.01 in multiple analysis). Diaphragm thickness and thickening fraction showed no significant associations with muscle mass. Diaphragm excursion could be an adequate indicator of sarcopenia in cases where limb-based measurement is not possible, and therefore unreliable.