Quadriceps function and patellofemoral pain syndrome. part i: Pain provocation during concentric and eccentric isokinetic activity

This study examines the relationship between force moments generated by the quadriceps femoris muscle group during concentric and eccentric isokinetic activity and the level of patellofemoral pain experienced in patellofemoral pain syndrome (PFPS) patients. The experimental population consisted of 55 patients with active PFPS (21 females, 34 males; mean age 21.1 yr; age range 19–42 yr) who were tested both concentrically and eccentrically on a Kin/Com isokinetic dynamometer system through a 0–90 deg flexion arc of knee motion. Testing consisted of four maximal efforts of concentric quadriceps femoris activity followed by eccentric activity, separated by a 10-s pause, across the speeds of 30, 60, and 120 deg/sec. The subject's patellar pain level was assessed throughout the testing process using the Borg Category Ratio Scale. Analysis of variance with repeated measures determined that pain perception did not vary between female and male subjects, even though male quadriceps output was significantly greater than that of females, and that eccentric activity produced significantly greater pain than concentric activity. It was concluded that an inverse relationship exists between PFPS pain and isokinetic velocity and that a close association exists between level of pain and magnitude of joint load.