An evaluation of knee extensor and knee flexor torques and EMGs in patients with patellofemoral pain syndrome in comparison with matched controls

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Abstract
The relationship between concentric and eccentric isokinetic torques and EMGs of quadriceps and hamstring muscles in patients with unilateral patellofemoral pain was studied in 27 patients (13 males, 14 females). The patients and a group of controls matched for age, gender, and physical activity were tested on a Kin‐Com dynamometer at 600/s and 1800/s angular velocity. EMGs were recorded for eight of the patients and their matched controls. In addition, the reproducibility of isokinetic measurements made under the same conditions but on different occasions in patients with patellofemoral pain was evaluated. Twenty‐one patients (11 males, 10 females) underwent testing of their quadriceps and hamstring muscles two or three times on a Kin‐Com dynamometer. This was performed both concentrically and eccentrically in their painful leg while the patients evaluated their knee pain using Borg's pain scale. The data show that the patients had a significantly lower agonist as well as antagonist EMG activity during knee extension measurements in their painful leg compared with the controls. However, there were no differences in either agonist or antagonist EMG activities during knee flexion measurements between the patients and the controls. The quadriceps muscle torque was considerably weaker in the patients' painful leg compared with both their asymptomatic leg and with the controls. Peak torque for knee extension was reached at a mean of 660 of knee flexion for both patients and controls. However, the patients showed a considerably wider range within which they produced their peak torque in their painful leg than in their asymptomatic and also in comparison with the controls. The hamstring muscle torque was weaker in both legs of the patients compared with the controls. There were no significant differences in knee pain according to Borg's pain scale between the isokinetic tests or within the tests. The reproducibility testing yielded no significant differences between the different testing occasions in the two muscle groups. In summary, patients with patellofemoral pain have a greatly reduced agonist and antagonist EMG activity during knee extension in their painful leg. They also have a considerably reduced quadriceps torque. Furthermore, isokinetic testing in patients with patellofemoral pain is a reproducible testing modality.

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