Tendinopathy is a major medical problem associated with sports and physical activity. It is an overuse injury where degenerative changes are present inside the tendon. The prevalence of patellar tendinopathy is highest in sports that contain a high amount of jumping. Eccentric exercise into tendon pain is recommended for treatment of patellar tendinopathy. Previous studies had shown that the use of decline eccentric single-leg squats is more effective to reduce tendon pain and improve function than standard eccentric single-leg squats. The aim of this study was to compare the electric activity of muscles during eccentric contraction in a single-leg squat on a flat surface and on a 25-degree decline board. 28 physically active and uninjured subjects participated in the study. Surface EMG signal of vastus lateralis, vastus medialis, rectus femoris, medial head of the gastrocnemius and soleus was recorded. EMG signal was normalised on the amplitude of EMG signal in maximal voluntary isometric contraction. The average value of the normalised EMG signal between a 60-degree and a 70-degree knee flexion angle was compared. Wilcoxon test was used to compare normalised EMG signal values in both variations of the squat, the significance level was set at 5%. The results show that electric activity of vastus lateralis, vastus medialis, rectus femoris and medial head of the gastrocnemius is significantly higher in a decline squat compared to a standard squat. No difference was found in soleus activity. Higher activity of quadriceps muscle could be one of the factors for greater patellar tendon force and consequently a greater effect of a decline squat on function improvement and pain reduction following patellar tendinopathy.
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