Cut-off points for knee extension strength: identifying muscle weakness in older adults

Generalized muscle weakness is the primary characteristic of sarcopenia. Handgrip strength (HGS) is widely employed to detect muscle weakness. However, knee extension strength (KES) declines much earlier and more pronounced than HGS, and there is a stronger correlation between KES and functional performance. Therefore, KES may be a more appropriate proxy for identifying muscle weakness compared to HGS. The purpose of this review was to clarify the KES measurement towards a standardized approach and summarize the cut-off points for KES.

A literature search was conducted in Web of Science, PubMed, Elsevier, Scopus and Medline databased up to July 10th, 2023.

A total of 12 articles were ultimately included in this review, which proposed various cut-off points for KES. Notably, these studies exhibited high heterogeneities, including diverse living settings for participants, KES measurement, methods for KES normalization, methodologies for determining cut-off points and study designs.

No consensus on cut-off points for KES was reached due to the heterogeneities in KES measurement and normalized methods among studies. To enhance the comparability among studies and facilitate the sarcopenia screening framework, a standardized approach for KES measurement and KES normalization are needed. Regarding KES measurement, the hand-held dynamometer-based isometric KES is easy to access and ideally suited for both clinical and community settings, while isokinetic KES, representing the gold standard, is preferred for research settings. Additionally, it is suggested to normalize isometric KES to body weight (BW), while normalizing isokinetic KES to allometrically scaled BW.