Back squat biomechanics, hypertrophy and anthropometry Part II

 Part II

The anthropometry and biomechanics associated with squats are the topic of this second part, where I examine different squat positions and their effects on different parts of the body. Demers et al. 2018, Gomes et al. 2020 have studied various physical characteristics, such as the length ratio of the legs and the flexibility of the joints in relation to squats. In particular, the ratio of the length of the femur and tibia became an important factor, because in squats, the flexion and extension of the hip and knee are carried out by the movement of the femur and tibia. A study by Demers (2018) found that a higher femur-tibial ratio is associated with greater dorsiflexion and knee flexion muscles, especially in squats with a narrow leg position. According to MacKea et al. (2012) used 3D kinematic analysis to investigate possible differences in movement between men and women during squats. According to the study, men lean somewhat more forward, which gives the spine movement and depth into a squat. Women, on the other hand, use the knees and sacrum to achieve the depth of the squat, also using the hip flexion more strongly. The use of knees was more pronounced in women, and taller women had a larger knee angle than shorter women. Taller men, on the other hand, emphasized smaller hip angles. At least the benefit of the study is that men and women use different movement strategies in squats, in which case it should be taken into account in both coaching and rehabilitation. The purpose of the study of Kim et al. (2021) was to investigate the relationships between physical characteristics and lower limb biomechanics during squat movement. They were trying to find out whether there are also gender differences in these. They measured the ratio of femoral to tibial length, mobility of hip and ankle joints, and relative muscle strength. However, no significant gender difference was observed in these factors in this study. The biomechanics of the lower limbs have been shown to correlate more with relative muscle strength and joint mobility than with the length ratio of the legs.

Another interesting aspect of anthropometry is related to the length of the femur. Cooke et al. (2019) studied the effects of hamstring length on the number of repetitions of the squat movement. The result was that the subjects with the longest femur were able to do significantly fewer repetitions than the subjects with the shortest femur. The results also revealed that body mass, fat percentage, and femoral length are all inversely related to repetitions performed at 70% of 1RM in the back squat. Longer femoral limbs and longer muscle lengths also seem to be associated with greater muscle damage (Nogueira et al. 2011) and weakening of muscle function during contraction (Behrens et al. 2012). 

Photo by Leon Ardho 

The review of  Escamilla et al. (2001) focused on the shear and compression forces of the lower leg and femur (tibiofemoral), the compression forces of the kneecap and femur (patellofemoral), and the activity of the extensor and flexor muscles of the knee. According to this, athletes with healthy knees can be recommended to squat horizontally (i.e. where the femur goes horizontally) instead of deep squats, because the risk of injury to the meniscus, cruciate ligaments and collateral ligaments may increase with deep squats. However, squats do not compromise the stability of the knee and can even increase stability when performed correctly. According to the review, squats are found to be an effective developer of hip, knee and ankle muscles, as it involves moderate to high activity in the muscles of the front thighs, hamstrings and calves.

A wider squat position is recommended if the goal is to optimize the development of hip adductors and hip extensors (e.g. gluteal muscles) (Miyamoto et al. 1999). A narrower squat position is more effective in targeting the development of the calf muscles (m. gastrocnemius) (Escamilla et al. 2001). On the other hand, the squat position can also be varied to alter the forces related to the joints, since the narrow position helps to reduce the compressive forces (both patellofemoral and tibiofemoral). The wide squat position causes the smaller knee translation forward, reducing the shear forces (Escamilla et al. 2001).

Recommended squat technique to minimize risks

Gaze	Backbone	Depth	Knee angle	Feet
Forward or up	Neutral, straight, lumbar lordosis	Preservation of lumbar lordosis as an indicator	115° to 125° Knees freely over the feet during movement No illumination, i.e. turning inward	Neutral Heels on the ground

 

Finally, it should be noted that in addition to the sport-specific squat technique, athletes should also practice various squat variations for the sake of training variety, preventing overuse injuries, and ensuring progress. This also applies to other trainees: it is beneficial to switch up different positions and vary the use of machines and free weights. On the other hand, it is important to consider the trainee's anthropometric characteristics, so that the squat technique can be fine-tuned to their proportions, making it an optimal and less risky exercise. For example, individuals with a torso-to-limb ratio shorter than average typically also have relatively longer femurs. The formula used to calculate the relative length of the femur has been applied in some studies as follows: (femur length / total body length) x 100%. The typical relative femur length is 25%, and a larger number indicates that it will affect the biomechanics of the squat. A safe squat position in this case would be a narrower/shoulder-width stance with a platform under the heels. Weightlifting shoes with a raised heel work well too. This helps avoid harmful compressive and shear forces on the lumbar spine and sacroiliac joint, alleviates pressure on the straightening of the lumbar lordosis and rounding of the lower back. The squat position thus remains more upright, with the back in a neutral position. All of this significantly reduces the risk of a herniated disc. On the other hand, squat depth can be influenced by a wider foot stance if the goal is to achieve the deepest squat possible.

 

Photo: Squat (Photo by Leon Ardho from Pexels: https://www.pexels.com/photo/photo-of-man-lifting-barbell-1552106/)

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