Contracted and relaxed quadriceps muscle thickness: A marker for muscle strength and probable sarcopenia?

BackgroundResting quadriceps muscle thickness (QMT) is known to be associated with muscle strength; however, the clinical relevance of contracted QMT in identifying muscle weakness has not been fully clarified.ObjectiveThis study aimed to investigate the relationship between resting and contracted QMT and isometric peak knee-extension torque (PT) and to evaluate the diagnostic value of contracted QMT in predicting probable sarcopenia (PS).MethodsForty-two individuals with PS and sixty-two healthy controls were evaluated. QMT and PT were compared between groups. Linear regression analyses examined the associations between QMT, handgrip strength (HGS), and appendicular skeletal muscle mass. Logistic regression and receiver operating characteristic (ROC) analyses assessed the diagnostic performance of contracted QMT.ResultsIndividuals with PS had lower contracted QMT and knee-extension strength than controls (all p < 0.01). Contracted QMT, rather than relaxed measurements, showed positive associations with HGS and appendicular skeletal muscle mass (ASMM) (all p < 0.05). Contracted QMT independently predicted PS (OR = 0.90, 95% CI: 0.82-0.99), and ROC analysis indicated moderate discriminatory performance (AUC range: 0.62-0.77).ConclusionsWhile both measurements were reduced in PS, contracted QMT showed a stronger association with muscle mass and strength. These findings suggest that contraction-based ultrasound parameters may serve as a preliminary and exploratory adjunct for identifying early functional decline. However, given the moderate discriminatory power, further standardization and external validation are required before routine clinical adoption.