Association of respiratory muscle strength with pre-frailty and overall functional status in community-dwelling Japanese older adults: a cross-sectional study

Physical frailty is marked by diminished physiological reserve and increased vulnerability. Pre-frailty, an intermediate state, is prevalent among community-dwelling older adults and linked to functional decline. This study examined the association between respiratory muscle strength and pre-frailty (primary outcome) and overall functional status (secondary outcome) in community-dwelling older adults in Japan. In this cross-sectional study, 324 adults aged ≥ 65 years participated in a community health survey in Fukushima Prefecture (August 2024–February 2025). Respiratory muscle strength was measured using maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP). Frailty status was assessed with the revised Japanese Cardiovascular Health Study criteria. Participants classified as frail (score 3–5) were excluded, leaving 313 individuals for analysis, comparing pre-frailty (score 1–2) with robustness (score 0). Functional status was evaluated using the Kihon Checklist (KCL), grip strength, knee extension strength, walking speed, and skeletal muscle index (SMI). Multivariable logistic regression models were constructed separately for MIP and MEP, adjusting for age, sex, body mass index, smoking status, and respiratory disease history. Lower MIP ( p < 0.001) and MEP ( p = 0.002) were significantly associated with greater odds of pre-frailty in both crude and covariate-adjusted models. In secondary analyses of overall functional status, lower MIP was significantly associated with higher KCL scores and lower grip strength, knee extension strength, walking speed, and SMI. Moreover, lower MEP was significantly associated with higher KCL scores and lower grip strength, knee extension strength, and walking speed, whereas its association with SMI was not significant after adjustment. Receiver operating characteristic analyses showed only modest discriminatory ability for identifying pre-frailty. Respiratory muscle strength is associated with pre-frailty and overall functional status in community-dwelling older adults and may be one of several factors associated with early vulnerability. Not applicable.