The Squat Biomechanics
The squat exercise is a close-chain movement with an angular motion of the thigh about the hip joint, angular motion of the leg about the knee joint, and angular motion of the foot about the ankle joint. Ankle dorsiflexion causes knee flexion and ankle plantar flexion produces knee extension, and hip extension produces knee extension and hip flexion produces knee flexion (Hamill et al., 2015).
The squat exercise involves a substantial group of muscles of the hip, thigh, leg, ankle, and spine joints. Starting from the standing position, hip, knee, ankle, and spine muscles contract isometrically. In descending phase, hip, knee, and ankle joint muscles contract eccentrically. During ascending phase, hip, knee, and ankle joint muscles contract concentrically.
The extensors muscle group of the hip joint includes the hamstrings muscles group (biceps femoris, semitendinosus, semimembranosus) and gluteus maximus.
The knee extensors muscle group include rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius. Plantar flexors of the ankle include plantaris muscles and the triceps surae muscle, the gastrocnemius, and soleus, which are used during the concentric and eccentric phases.
The group of spine erector muscles, including the longissimus muscle group, iliocostalis muscle group, and spinalis muscle group, which are isometric during all phases of the move (Hamill et al., 2015). In the squat position all muscle groups of the hip, knee, and ankle is contracted isometrically.
References
Hamill, J., Knutzen, K. M., & Derrick, T. R. (2015). Basic Terminology. In Biomechanical Basis of Human Movement, 4th Ed. Wolters Kluwer.
Lorenzetti, S., Ostermann, M., Zeidler, F., Zimmer, P., Jentsch, L., List, R., Taylor, W. R., & Schellenberg, F. (2018). How to squat? Effects of various stance widths, foot placement angles and level of experience on knee, hip and trunk motion and loading. BMC sports science, medicine & rehabilitation, 10, 14. https://doi.org/10.1186/s13102-018-0103-7
Schoenfeld B. J. (2010). Squatting kinematics and kinetics and their application to exercise performance. Journal of strength and conditioning research, 24(12), 3497–3506. https://doi.org/10.1519/JSC.0b013e3181bac2d7
