The preceding eccentric phase enhances mechanical output within the sticking region during the squat: A biomechanical...

The sticking region is a common mechanical disadvantage during resistance training, and the load that can be tolerated in this phase directly determines overall training load and performance. However, the biomechanical characteristics of the sticking region have not been sufficiently clarified, which limits the development of targeted strategies to improve force production and training stimulus during this critical phase. Therefore, this study aimed to systematically examine the biomechanical characteristics between the 1RM free-weight squat and posture-matched maximal isometric squat within sticking region, in order to explore the potential contribution of the preceding eccentric phase in this region.

Thirty resistance-trained male collegiate participants performed one repetition maximum (1RM) squats and isometric squats at different heights. Biomechanical data were collected simultaneously using an integrated system consisting of an infrared three-dimensional motion-capture system, a force platform, and surface electromyography (sEMG).

Compared with the isometric squat, the 1RM squat produced significantly greater vertical ground reaction force (vGRF, p < 0.001), greater hip and knee extension torques, and a greater ankle plantarflexion torque (p = 0.001-0.029), as well as greater normalized sEMG amplitudes in the vastus medialis, tibialis anterior, lateral gastrocnemius, and medial gastrocnemius (p = 0.001-0.022).

During the free weight squat, the sticking region is characterized by a marked reduction in force output and joint torque, confirming it as a key mechanical disadvantage in the movement. The additional mechanical demands associated with the eccentric phase significantly increased joint torque output and the activation levels of major muscles during the squat. These findings highlight the potential value of eccentric-focused strategies for enhancing force production during this critical phase of the squat.