Patellofemoral pain (PFP) is characterized by non-traumatic and diffuse pain over the anterior aspect of the knee which is aggravated by activities that increase patellofemoral joint compressive forces. Lower knee extensor torque is common in patients with PFP, however, the causes responsible for maintaining this deficit, even after treatment, are not fully understanding. Recently, it was found that the amplitude of the Hoffmann reflex (H-reflex) of the quadriceps femoris is lower in women with PFP, indicating spinal excitability impairments in this muscular group. In this sense, it is justifiable the hypothesis that neurophysiological impairments, such as lower amplitude of the H-reflex, may be related to lower torque of the knee extensors in individuals with PFP. This finding may suggest a change in the current paradigm of PFP approach, with the addition of interventions aimed at increasing spinal excitability of these patients, in order to enable the adequate strengthening of the knee extensor muscles. Thus, the overall objective of this project is to determine whether the lower H-reflex is associated with the lower knee extensor torque parameters in women with PFP and asymptomatic. Therefore, a cross-sectional study will be performed, in which women with PFP and asymptomatic between 18 and 35 years old will be recruited. The volunteers will perform isometric, concentric and eccentric contractions of the knee extensor muscles in an isokinetic dynamometer. The H-reflex will be recorded by electromyography using surface electrodes placed on the vastus medialis muscle. The data will be processed and, subsequently, Pearson or Spearman correlation coefficients will be calculated, depending on the data distribution, to verify the relationship between the amplitude of the H-reflex with the parameters of the knee extensor torque. For all tests it will be adopted the significance level of p <0.05.
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