To evaluate the association between lower-limb muscle power (MP) and frailty, measured using eight different scales, in older adults from four clinical settings. Additionally, to examine the predictive capacity of MP for adverse health events.

A cross-sectional and longitudinal analysis using data from the Spanish cohort of the Frailtools project.

Nursing homes, primary care clinics, geriatric inpatient wards, and outpatient clinics.

245 older adults (mean age 82 ± 4.6 years, 64% women).

MP measures were estimated using the five-time sit-to-stand (5STS) test and validated equations to obtain absolute (AMP), relative to body weight (RMP), and allometric (ALMP) values. Frailty was evaluated using eight scales, including the Frailty Phenotype and the Frailty Trait Scale. The incidence of adverse events (e.g., frailty, hospitalization, falls, and disability) was recorded over 12 months.

Frailty prevalence varied significantly across scales and settings, with the lowest rates observed in primary care and the highest in nursing homes. Cross-sectional analysis revealed significant associations between all MP measures and frailty for most scales. RMP demonstrated the strongest associations, particularly with the Frailty Trait Scale-5 and FRAIL scale, across primary care, nursing homes, and outpatient clinics. Longitudinally, RMP was significantly associated with incident frailty and several adverse events, including hospitalizations (AUC: 0.71) and disability in activities of daily living (AUC: 0.71). Sex-specific MP cut-off points were identified for predicting health events. No significant differences were observed among MP measurements.

Lower-limb MP is a valid clinical biomarker associated with frailty and negative health events in older adults. The degree of associations varied according to frailty scale and clinical context, but no significant differences were observed when we compared their predictive ability. The proposed MP cut-off points may enhance frailty assessment and screening, particularly in primary care, nursing homes, and outpatient clinics. These findings highlight the clinical potential of incorporating MP measures into frailty tools and stress the need for further research to refine age-specific cut-off points and explore the influence of body composition.