One-repetition submaximal protocol to measure knee extensor muscle strength among older adults with and without sarcopenia: a validation study.

Background: Dynamic knee extensor muscle strength is a valid measure among healthy older adults but has not been tested in the sarcopenia condition. This study's objective was to test the validity of a one-repetition submaximal strength protocol to measure dynamic knee extension strength in older adults with and without sarcopenia. Methods: Ninety-four physically independent older adults (female: n = 64, 60 to 85 years; male: n = 29, 60 to 85 years) participated in this study in Brazil during 2016-2017. Sarcopenia was classified and isokinetic unilateral knee extension strength was measured at 60°/s. Bilateral dynamic knee extension strength was estimated with an extensor chair using one-repetition submaximal protocol. Validity was determined using Spearman's correlation with isokinetic muscle strength. Results: The frequency of sarcopenia was 11.7%. Sarcopenic individuals presented lower body mass, body mass index and skeletal muscle index. Only chronological age was higher among the sarcopenic individuals. A high correlation was found between isokinetic unilateral knee extension strength and bilateral estimated one-repetition with submaximal protocol (r = 0.74; p <  0.001), when the presence (r = 0.71; p = 0.014) and absence of sarcopenia (r = 0.74; p <  0.001) were considered. The validity of the one-repetition submaximal protocol for bilateral knee extension was confirmed. Conclusions: The estimated measure of bilateral knee extension muscle strength can be used to monitor adaptations promoted by physical exercise for older adults with and without sarcopenia. The validation enable studies that will propose cutoff points to identify sarcopenia with this submaximal protocol. This will enable early diagnosis and better management of sarcopenia, a disease with adverse impacts for older adults.