This study investigated the quadriceps muscle activity during eccentric squat exercises (ESE) with different decline angles and arcs of motion regarding the proper exercise selection for patellar tendinopathy management. Electromyographic activity of the rectus femoris, vastus lateralis, and vastus medialis obliquus (VMO) muscles was measured during ESE on 0°, 5°, 10°, 15°, and 20° decline in 20 recreationally active participants. The eccentric phase was divided into 0–30°, 30–60°, 60–90°, 0–60°, 30–90°, and 0–90° of knee flexion simultaneously via motion-analysis system. The analyses showed that there was a significant decline angle × arc interaction effect on electromyographic activity of all muscles during knee flexion movement. The main effect was found for the arc of motion of knee flexion, and the main effect for the decline angle also was present for each muscle, except for VMO. This study demonstrated that most selective quadriceps eccentric activation occurred during ESE performed on 20° decline throughout 60–90° of knee flexion.

Background. Simultaneous tiredness of two or more muscles around a joint can be defined as coordinated fatigue (co-fatigue) and might occur between agonist and antagonist muscles, and vary according to the level of sporting activity levels or gender. Objectives. The aim of this study was to determine the levels of coordinated ...