Quadriceps function and patellofemoral pain syndrome. part ii: The break phenomenon during eccentric activity

The isokinetic moment-angular position curves of the quadriceps femoris were studied in a group of 21 women and 34 men presenting with patellofemoral pain syndrome (PFPS). The study focused on a specific irregularity of the torque curve, namely a sudden "break" in the monotonicity of the curve. Breaks appeared in 47% and 44% of the female and male groups, respectively, and during eccentric activity, exclusively, predominantly at the velocity of 30 deg/sec. The break occurred close to the location of the peak torque moment, at an average angle of 45 deg flexion, and lasted for about 10 deg in the total arc of motion. The extent of load reduction due to the break effect was 25%-30% of subject body weight. A close association between the pain provoked during isokinetic loading and the break phenomenon was indicated in all subjects. The results suggest the applicability of incorporating analysis of the break phenomenon in the evaluation of patients with active PFPS.