The purpose of this study was to investigate 3D kinematics and muscle activation around the sticking region (the weakest region) in full back squats. Eleven resistance-training males (age 23.5 ± 2.6 years, body mass 86.8 ± 21 kg, body height 1.81 ± 0.08 m) performed 6-RM full squats and the last repetition was taken for further analyses of 3D kinematics and EMG activity around the sticking region. The main findings were that all participants exhibited a sticking region during the last repetition of the 6-RM squatting. The rectus femoris activity decreased in each region from the pre-sticking to the sticking region, the lateral vastus only decreased from the sticking to the post-sticking region, while a significant increase in EMG activity was found for the glutei muscles from the pre-sticking to the sticking region. In addition, the timing of the peak and minimal angular velocities of the hip extension, knee extension and plantar flexion movements were concomitant with the two peak velocities and minimal velocity of the barbell. It is suggested that the timing and activity between the knee extensors (lateral vastus, rectus femoris) and the gluteus maximus are responsible for the existence of the sticking region together with the large joint moment arms in this region.
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