Medial gastrocnemius muscle architecture assessed by ultrasound is associated with fear of falling and functional mobility in postmenopausal women with osteoporosis

Abstract Objective Osteoporosis in postmenopausal women is associated not only with reduced bone mineral density but also with alterations in muscle morphology and architecture, which may contribute to impaired balance, decreased functional mobility, and an increased risk of falls. The medial gastrocnemius muscle plays a critical role in postural control and gait, and ultrasonographic assessment allows detailed evaluation of its structural and architectural properties. Fear of falling is a common and clinically relevant psychological factor in individuals with osteoporosis, as it may further limit mobility and functional independence. However, the relationships between ultrasonographic characteristics of the medial gastrocnemius muscle, fear of falling, and functional mobility in postmenopausal women with osteoporosis have not been fully elucidated. Methods In this cross-sectional observational study, 44 postmenopausal women with osteoporosis confirmed by dual-energy X-ray absorptiometry (DXA) were included. Medial gastrocnemius muscle thickness, pennation angle, and fascicle length were assessed using musculoskeletal ultrasonography. Fear of falling was evaluated with the Falls Efficacy Scale–International (FES-I), and functional mobility was assessed using the Timed Up and Go (TUG) test. Participants were categorized into low and high fear-of-falling groups according to the established FES-I cut-off value. Between-group comparisons and associations among variables were analyzed using appropriate statistical methods. Results Compared with the low fear-of-falling group, the high fear-of-falling group had significantly lower medial gastrocnemius muscle thickness (9.88 ± 1.41 mm vs. 12.62 ± 1.21 mm; p < 0.001), pennation angle (16.1 ± 3.9° vs. 19.4 ± 3.2°; p = 0.008), and fascicle length (42.3 ± 8.6 mm vs. 51.6 ± 7.9 mm; p = 0.001). In addition, TUG time was significantly longer in the high fear-of-falling group (14.92 ± 2.21s vs. 12.18 ± 1.84s; p < 0.001). Correlation analyses showed significant negative associations between medial gastrocnemius muscle thickness and FES-I total score ( r = − 0.329; p = 0.029) as well as TUG time ( r = − 0.308; p = 0.042). Pennation angle and fascicle length were also significantly and negatively correlated with both FES-I score ( r = − 0.392 to − 0.448) and TUG time ( r = − 0.417 to − 0.472) (all p < 0.01). Conclusion In postmenopausal women with osteoporosis, impairments in medial gastrocnemius muscle architecture appear to be associated with greater fear of falling and reduced functional mobility. These findings suggest that fall-related evaluations in individuals with osteoporosis may benefit from integrating muscle structural characteristics with functional and psychological components such as fear of falling.