Grip and knee extension strength have each been used to characterize muscle strength. Whether grip and knee extension strength reflect a common construct was investigated. Bilateral isometric grip and knee extension strength measures obtained by dynamometry were retrieved from the records of 34 adults who were at least 60 years of age (M = 80.2 yr., SD = 8.1) and had diverse non-focal diagnoses or problems. Relations between measurements were examined using Pearson correlations, Cronbach's alpha, and factor analysis. Pearson correlations (r = .55 to .89), Cronbach's alpha (.88), and factor analysis (loadings .85 to .91) all suggest that grip and knee extension strength reflect a common construct. Either grip or knee extension strength, therefore, may be adequate to characterize limb muscle strength in older adults who are receiving physical therapy for diverse non-focal diagnoses or problems. Nevertheless, the measurement of grip strength may be preferred because it is easier.