Predictive value of different muscle power normalization methods for mobility limitations in community-dwelling older adults: A cross-sectional analysis from the longevity check-up 8+ study

Background: Lower limb muscle power is a critical determinant of mobility in older adults. However, its optimal normalization method remains uncertain. The aim of this cross-sectional study is to compare different normalization approaches for muscle power in predicting self-reported 400 m walking difficulty, used as a proxy of mobility limitation, in community-dwelling older adults (≥65 years old) from the Longevity Check-Up 8+ Study. Methods: Lower limb muscle power was estimated using five-repetition sit-to-stand equations and expressed as i) absolute (W), ii) relative (W/kg), iii) allometric (W/m2), and iv) specific power (W/kg of appendicular skeletal muscle mass). 400-m walking difficulty was self-reported and dichotomized. Discriminative ability was assessed through receiver operating characteristic curves. Associations were tested using logistic regression models. Results: Among the 4614 participants (mean age 72.8 ± 5.8 years; 53.2 % women), 25.1 % reported difficulty walking 400 m. Individuals reporting difficulty were older, more frequently female, had higher body mass index, and lower physical activity levels (all p < 0.001). Relative muscle power demonstrated the highest discriminative ability [area under the curve 0.70; 95 % confidence interval (CI) 0.68-0.72], outperforming other indices. Optimal cut-offs for relative muscle power identified using the Youden index were 3.1 W/kg in women and 3.8 W/kg in men. Low relative muscle power was significantly associated with greater odds of walking difficulty (odds ratio 2.07; 95 % CI 1.78-2.42; p < 0.001). Conclusions: Relative muscle power showed superior predictive performance for self-reported walking difficulty, as an indicator of mobility limitation, compared to other normalization methods. Future longitudinal studies are needed to confirm these findings and explore their relevance for other clinically meaningful outcomes.