The back squat is a common exercise in strength and conditioning for the development of muscular strength and hypertrophy of the lower limbs. It represents an essential human pattern of movement, since it involves the flexion / extension of the lower limbs (Read our review on the deep squat).
Squat is a closed kinetic chain exercise that requires the bar and center of gravity to be constantly balanced over the mid-feet throughout the entire movement. The joint angles of the various body segments involved must thus be coordinated to maintain this balance at every moment. Since the hips will move backward, the balance will be mainly maintained by the knees going forward or by a forward trunk lean (Read our article on the forward knee movement in squat).
In back squat, lower back injuries are common, and practitioners are often advised to maintain a neutral, upright spine. This is not always easy, because the taller athletes tend to have the lowest trunk-thigh angle, that is, they lean more forward, or they realize a deeper squat. Similarly, limited ankle dorsiflexion will limit the forward knee movement and therefore will cause a more pronounced forward trunk lean. To limit this, wearing weightlifting shoes or placing an iron plate under the heels will allow forward knee movement by simulating a shank-ground angle. But what influences most the forward trunk lean? Ankle dorsiflexion or segment ratios ?
Figure 1. Diagram of the segments and articular angles observed, (1) Ankle dorsiflexion and (2) Forward trunk lean.
To answer these questions, a Danish research team investigated the links between parallel squat kinematics, ankle dorsiflexion, and segment ratios. For this protocol, 11 recreational athletes took part in the experiment. All had been practicing resistance training and parallel squat for at least 18 months (1RM estimated = 136.8 ± 24.4 kg). The tests consisted of performing 3 squat repetitions parallel to the ground with 80% of 1RM, then performing a mobility test to evaluate ankle dorsiflexion.
For the parallel squat, all participants performed barefoot with their feet straight forward with a shoulder width stance (since larger stance would require less ankle dorsiflexion). Once the squat was completed, all participants performed a maximum dorsiflexion test. The position was maintained for 3 seconds, and participants were allowed three trials for each ankle.
During all the tests, reflective markers were positioned on the participants to measure the length of the various body segments (trunk, thigh, shank) and joint angles in the sagittal plane using a 3D motion capture system (Fig. 1).
The main results of this study show that there is a difference (11.4 ± 4.4 °) between the maximum dorsiflexion measured during the test and the dorsiflexion reached during the parallel squat. The ankle dorsiflexion is lower during parallel squats. In addition, only a significant relationship between the angle of the shank during the test and that during the parallel squat and a significant relationship between the angle of the trunk and the angle of the shank during the test were observed. No significant relationship was found between segment ratios and forward trunk lean (except for the trunk/thigh ratio), even when segment ratios were combined with ankle dorsiflexion.
The deficit of ankle dorsiflexion in squat seems normal because the two situations are totally different. During the maximum amplitude test, participants are not required to line up both feet on the same line or to think about handling a load on their shoulders. In addition, the deficit was statistically independent of maximal dorsiflexion, suggesting a natural deficit between the two situations. In addition, only 41% of variations in ankle dorsiflexion in parallel squat are explained by the dorsiflexion test.
For the parallel squat, when the shank-ground angle decreases, the trunk-thigh angle increases. These results account for about 45% of the variance of the angle of forward trunk lean. These results show that forward knee movement allows, partially, the improvement of the forward trunk lean (that is, a larger trunk-thigh angle). The authors also report that only the trunk/thigh ratio had a positive influence on forward trunk lean.
However, in this study, variation in segment length was small, weakening the predictive effect of multiple regression models. It would take a larger group with more anthropometric differences to reinforce the prediction of these statistical models.
To balance squats and compensate for backward hip movement, an athlete must either lean the trunk forward or move the knees forward with ankle dorsiflexion. The greatest requirement for forward trunk lean and/or ankle dorsiflexion is when the hips and knees are farthest from each other in the sagittal plane, that is, during the squat parallel.
The forward trunk lean is often criticized and considered dangerous because it increases the shear forces at the level of the lumbar vertebrae. This type of practice will be even more dangerous if it is coupled with a lack of mobility in the hips, a lack of muscle strength and a load too important relative to the strength of the athlete. In addition, the squat movement should not turn into "Good morning" and maintain a better mechanical efficiency by maintaining a trunk as vertical as possible.
It is therefore understandable that for competitors, the weightlifting shoes are useful. Stretching or self-myofascial release on the extensor ankle muscles and mobilization with movement on the joint can help improve the range of motion in dorsiflexion. It remains to be seen whether an increase in the range of motion in dorsiflexion using these methods will change the trunk lean... In all cases, athletes with a very limited dorsiflexion will be those who will benefit the most from an improvement in comparison to athletes with a good dorsiflexion.
The dorsiflexion test can be used by the coaches to see if the forward trunk lean is caused by a restriction in the range of motion of the ankle. If the athletes have a good test, but they lean too much forward in squat, it is necessary to work on the pattern of movement. For those who have a poor test result and who lean too far forward, it will be necessary to improve dorsiflexion of the ankle using the methods mentioned above.
Finally, for athletes who have a disadvantageous trunk/thigh ratio and limited ankle dorsiflexion, squats may not be the best exercise choice. And it is not the only one to allow an efficient work for lower limbs.
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