Comparison of available equations to estimate sit-to-stand muscle power and their association with gait speed and frailty in older people: Practical applications for the 5-rep sit-to-stand test.

Abstract Objectives This study aimed i) to compare relative sit-to-stand power (STSrel) values yielded by the different equations reported in the literature; ii) to examine the associations between STSrel, derived from the equations, and age, sex, frailty and habitual gait speed (HGS); and iii) to compare the ability of the different STSrel equations to detect frailty and low HGS in older adults. Methods 1568 participants (>65 years) were included. STSrel was calculated according to four validated equations. Frailty was assessed using the Frailty Trait Scale and HGS as the time to complete 3 m. ANOVA tests, regression analyses and receiver operator characteristic curves were used. Results There were significant differences among the STSrel values yielded by all the equations, which were higher in men compared to women and negatively associated with age (r = −0.21 to −0.37). STSrel was positively and negative associated to HGS and frailty, respectively, in both men (r = 0.29 to 0.36 and r = −0.18 to −0.45) and women (r = 0.23 to 0.45 and r = −0.09 to −0.57) regardless of the equation used. Area under the curve values varied between 0.68 and 0.80 for Alcazar's, 0.67–0.80 for Ruiz-Cardenas's, 0.51–0.65 for Smith's, and 0.68–0.80 for Takai's equations. Low STSrel indicated an increased probability of having both low HGS and frailty (OR [95%CI] = 1.6 to 4.5 [1.21 to 5.79]) for all equations with the exception of Smith's equations for frailty in women. Conclusions All the equations presented adequate criterion validity, however, the Alcazar's equation showed the highest level of clinical relevance according to its ability to identify older people with frailty and low HGS.