Effect of Posture on Strength of the Knee Flexor and Extensor Muscles

¹ From the Detroit Orthopedic Clinic and Wayne State University, College of Engineering, Detroit, Michigan

A muscle dynamometer with a versatile supporting apparatus is described and used for studying the effect of posture on the strength of knee flexor and extensor muscles. Maximal effort tests in seven positions through a range of knee motion were performed by normal females in the sitting, supine and prone postures. The evidence presented suggests that the tests are highly repeatable in a prescribed posture and at a given angle of motion. The force developed by flexor and extensor muscle groups vary with the position of the knee and the hip. This in turn influences the ratio between the strength of these muscle groups. The posture of the subject has a greater effect on the realizable force developed at the knee than does the influence of gravity on the leg, or the stabilization of adjacent parts. The rationale for the results and the clinical application are discussed.