Identification of muscle weakness in older adults from normalized upper and lower limbs strength: a cross-sectional study

Abstract

Background To propose cut-off points for older adults’ weakness for upper and lower limbs muscle strength normalized by body size with the ratio standard/muscle quality and allometric scaling. Methods Ninety-four community-dwelling older adults (69.1% women) were assessed for 49 body-size variables (anthropometry, body composition and body indexes), handgrip strength (HGS), one maximum repetition measurement for knee extensors (1RM), isokinetic knee extension peak torque at 60°/s (PT), and six-minute walk test (6MWT). Ratio standard or muscle quality (muscle strength/body size) and allometric scaling (muscle strength/body sizeb; when b is the allometric exponent) were applied for body-size variables significantly correlated with HGS, 1RM and PT. Cut-off points were computed according to sex based on mobility limitation (6MWT < 400 m) with ROC curve and Youden index. Results Absolute HGS, 1RM and PT cut-off points were not adequate because they were associated with body size (r > 0.30). But it was corrected with muscle strength normalization according to body size-variables: HGS (n = 1); 1RM (n = 24) and PT (n = 24). The best cut-off points, with the highest area under the curve (AUC), were found after normalization for men: HGS/forearm circumference (1.33 kg/cm, AUC = 0.74), 1RM/triceps skinfold (4.22 kg/mm, AUC = 0.81), and PT/body mass*height0.43 (13.0 Nm/kg*m0.43, AUC = 0.94); and for women: HGS/forearm circumference (1.04 kg/cm, AUC = 0.70), 1RM/body mass (0.54 kg/kg, AUC = 0.76); and PT/body mass0.72 (3.14 Nm/kg0.72; AUC = 0.82). Conclusions Upper and lower limbs muscle weakness cut-off points standardized according to body size were proposed for older adults of both sexes. Normalization removes the effect of extreme body size on muscle strength (both sexes) and improves the accuracy to identify weakness at population level (for women, but not in men), reducing the risk of false-negative/positive cases.

Muscle Weakness and Walking Slowness for the Identification of Sarcopenia in the Older Adults from Northern Brazil: A Cross-Sectional Study

“…Among those outcomes, limited mobility is commonly the first sign and predisposes older adults to functional disability, falls [ 1 , 2 ], fractures, increased risk of depression [ 4 ], hospitalizations [ 5 ], institutionalization, and premature death [ 6 ]. It is noteworthy that limited mobility seems to be even more important than multimorbidity to forecast mortality amongst older adults [ 7 ]. As a result of its predictive ability, assessment of muscle weakness and assessment of walking slowness (as a marker of limited mobility) are used for the identification of geriatric syndromes such as sarcopenia, frailty, and the risk of falling [ 1 , 8 ].…”

“…Muscle weakness is usually assessed using an absolute muscle strength score [ 7 , 13 , 14 , 15 ] or by normalizing the absolute muscle strength to a body size variable [ 10 , 15 ]. Inaccuracy tends to increase in the first case, especially in older people with lower body mass and height [ 16 ].…”

Foreign allometric exponents adequately normalize isokinetic knee extension strength to identify muscle weakness and mobility limitation in Portuguese older adults: a cross-sectional study

“…While weak isokinetic knee extension is the best predictor of mobility limitation [13,14], current isokinetic strength indexes to identify mobility limitation are based on absolute strength results [15][16][17][18][19] or when normalized by body mass using ratio standards [20]. However, the "muscle weakness" phenotype may be incorrectly applied to older adults who have a lighter body mass and shorter stature using absolute cutoff points [21][22][23], even if they sustain their mobility [14].…”

“…The nonlinear relationship between isokinetic leg extension strength and body mass in older adults has been reported [13,26,27], with b varying between 0.37 to 0.74. Indeed, scaling isokinetic knee extension strength by body size removes the effect of body size on muscle strength [13].…”

“…The nonlinear relationship between isokinetic leg extension strength and body mass in older adults has been reported [13,26,27], with b varying between 0.37 to 0.74. Indeed, scaling isokinetic knee extension strength by body size removes the effect of body size on muscle strength [13]. Furthermore, where muscle strength was allometrically adjusted, the accuracy in identifying muscle weakness and mobility limitation was improved compared to non-normalized values in older adults.…”