Squat biomechanics, hypertrophy and anthropometry Part I

 Part I

Plotkin (2023)

I wanted to take a closer look at squats because they are one of the most commonly used exercises in both lower limb rehabilitation and resistance training. Squats are also a competitive sport in weightlifting, with its own regulations for proper squats. The recruitment of muscles, the forces exerted on the knee joint and the skeleton of the lower extremities are different depending on the placement of the legs and the depth of the squat, but also on individual anthropometric differences. The width of the squat position, the position of the feet and the depth of the squat can be varied according to goals and individual differences. However, it should be noted that various strain injuries, pain, damage to either the menisci or articular cartilage, and spondylolysis are examples of what the wrong squat technique can cause (Cappozzo et al. 1985, Comfort et al. 2018, Escamilla 2001, Fry et al. 2003, Miller et al. 1997, Vakos et al. 1994, Yack et al. 1993), so it is good to familiarize yourself with performance optimization also from a technical point of view. In this part, the first part, I will focus more on the muscular responses of the squat, and in the second part I will focus more on the technical aspects of the squat.

The differences between squat and hip thrust exercises and gluteal hypertrophy were examined by Plotkin et al. (2023). Both movements produced similar muscle growth, but the back squat also resulted in an increase in the thigh muscle. Also Delgado et al. et al. (2019) investigated differences in muscle activation in the back squat and hip thrust using surface electromyography. The anterior femur muscle (m. vastus lateralis), the hamstring muscle (m. biceps femoris) and the large gluteus muscle (m. gluteus maximus) were examined. The study also compared the Romanian deadlift (RDL) to the exercises mentioned before. According to the study, RDL was as effective as hip thrust exercise in activating hip extensors (e.g., glutes), while back squats simultaneously stimulate both hip and knee extensor muscles (quads). However, the study used the same load on all subjects, which may have affected the results to some extent.

In general, it is worth noting here that although squats are considered an exercise for the muscles of the lower extremities, it also activates other muscle groups. The core muscles, mainly the abdominal and spinal muscles, are significantly activated. (Anderson et al. 2005, Oddsson et al. 1999) However, according to the position of the lumbar spine, there is variation in the activation of the straight abdominal muscle, spine and wide back muscle (m. latissimus dorsi) (Vakos et al. 1994), and with respect to the gluteal muscles (m. gluteus maximus), better recruitment can be observed during deep squats. There do not appear to be significant differences in the relative proportions of the hamstring muscle and quads in the performance of this type of squat, according to the study. However, the proportion of quads (especially m. vastus medialis) seems to increase with increasing squat depth. (Caterisano et al. 2002) Thus, increased squat depth (half squat 45°, parallel squat 90°, full deep squat 125°) appears to result in a more efficient percentage of glutes during a full-depth squat. (Caterisano et al. 2002, Ninos 1997) In the eccentric phase, i.e. the descent phase, the relative proportions of the four muscle groups (m. vastus medialis, m. vastus lateralis, m. biceps femoris, m. gluteus maximus) in the three depths tested did not differ statistically. (Caterisano et al. 2002). Research generally suggests that, regardless of technique, squats don't activate the hamstring muscles much. (Escamilla et al. 1998 &; 2001, Ninos et al. 1997, Signorile et al. 1995)

However, foot rotation (neutral, 30-40° medial, 80° lateral rotation) has not been shown to have a noticeable effect on muscle function when examining the activation of the anterior thighs (m. rectus femoris, m. vastus medialis, m. vastus lateralis), thigh convergences (m. adductor longus) and hamstrings (m. semimembranosus, m. semitendinosus and m. biceps femoris). (Escamilla et al. 1998 &; 2001, Mc Caw et al. 1999, Ninos et al. 1997, Signorile et al. 1995) On the other hand, however, variations in posture width change muscle recruitment patterns, as a position larger than shoulder width increases the activity of the adductor muscles. (Ninos et al. 1997, Signorile et al. 1995)

The optimal squat technique minimizes the risk of injury, but maximally activates the muscles of the lower extremities. According to studies, this position is precisely the wide position of the feet, with the feet at a natural angle (Escamilla et al. 1998 &; 2001, Mc Caw et al. 1999, Ninos et al. 1997, Signorile et al. 1995), heels remain on the floor, knees move freely over the feet (Fry 2003, Panerillo 1994), and gaze is forward or upward. A full squat depth (115-125° knee angle) would be preferable, assuming that lower back lordosis, i.e. natural lumbar curve, remains good. (Caterisano et al. 2002, Ninos et al. 1997) It has previously been recommended that squats be performed at a knee angle of 0– (Escamilla et al. 2001) because the forces exerted on the knee structures increase with increased flexion (Escamilla et al. 2001) However, performance seems to improve when the squat is performed with a larger range of motion (Hartmann et al. 2002, Weiss et al. 2000) or when the low squat is used as a supplementary exercise for a full deep squat. (Bazyler et al. 2014) The results of the study of Kubo et al. (2019) suggest that full deep squat training is more effective in developing the muscles of the lower extremities, with the exception of the hamstring muscles.

Based on a review of Ribeiro et al. (2023), squats are an effective exercise to promote muscle growth of the foreleg muscles (especially m. vastus lateralis, medialis and intermedius, as well as m. rectus femoris, although less so in the latter one). According to this review, back squats appear to produce little or no hamstring muscle growth. Although the gluteus maximus is clearly mechanically involved in the posterior squat, there still seem to be relatively few longitudinal studies on the subject. However, deep squats may be more conducive to muscle growth for the glutes, and a squat depth exceeding the knee angle of 90° does not appear to increase hypertrophy of the knee extensors (quads).

 

Picture: Plotkin (2023): https://pmc.ncbi.nlm.nih.gov/articles/PMC10349977/figure/F5/

According to Plotkin et al. (2003) on a study of the effects of squats and hip thrust on glutes. In the picture, MRI (magnetic resonance imaging) muscle cross-sectional areas (a) left + right (L+R) upper so-called MRI scan. large gluteus maximus, b) L+R middle so-called. large gluteal muscle (m. gluteus maximus), c) L+R lower m. gluteus maximus, d) L+R m. gluteus medius+minimus. The graphs contain change points in which the values of individual participants are represented as points. (e) Three MRI scans before and after the MRI image are performed by the same participant with white polygon tracing of the upper gluteus maximus and gluteus medius+minimus (top) of L+R, the middle gluteus maximus of L+R (middle) and the lower gluteus maximus of L+R (bottom).

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