Clinical relevance of different muscle strength indexes and functional impairment in women aged 75 years and older

BACKGROUND: Muscle mass index has long been used as a useful index to evaluate the risks of developing functional impairments. However, there is evidence that other indexes (particularly muscle strength-based indexes) may be more relevant. Thus, the purpose of this study was to compare the association between different indexes of muscle mass or strength with self-reported and measured functional performance to determine which index would be clinically relevant to detect individuals at risk of functional impairments. METHODS: Data are from 1,462 women aged 75 years and older recruited in the Toulouse EPIDémiologie de l'OStéoporose cohort. Body composition (assessed by dual energy x-ray absorptiometry), handgrip, and knee extension strength were assessed. Physical function was measured using the chair stand test as well as the usual and fast gait speed tests. Participants were also asked if they experienced any difficulty at performing functional tasks. RESULTS: Results showed that knee extension strength relative to body weight was the strongest correlate of physical function measures (.30 < r < .40). Women in the lowest quartile of knee extension strength relative to body weight were 5.9-, 24.7-, 12.1-, and 20.9-fold, respectively, more likely to present impairments at self-reported activities, chair stand test, and usual and fast gait speed compared with women in the highest quartile, respectively. CONCLUSIONS: Knee extension strength relative to body weight appears to be well associated with self-reported difficulties and functional impairments. A threshold between 2.78 and 2.86 (knee extension strength [kPa]/body weight [kg]), determined using receiver operating characteristics curves analysis, may be a potential cut point to discriminate women presenting higher functional impairments.