Among resistance training exercises, the squat is the most popular for lower limb work. Often revered by some, he is also hated by others. He is frequently accused of causing injuries to the knees and the lower back, wrongly. It is usually the given instructions that can be more or less harmful and cause more harm than good (for example, the famous non-advanced knees beyond the tip of the toes, and if you do not have read it yet, we recommend our article on the subject). A misinterpretation of the scientific data and a lack of knowledge of the exercise have led many people to demonize this exercise, and the full squat is a very good example (you can read our review on this topic to learn more).
Figure 1. Weightlifting shoes (Click to enlarge)
The squat is in essence a very difficult exercise since it involves moving a relatively heavy load on the shoulders, in a large range of motion. In addition to the obvious strength qualities of the lower limbs, this exercise requires strong core and high mobility of the lower limbs, especially at the hips and ankles. And to maintain balance throughout the movement, the lifter has the opportunity to tilt the trunk forward or increase the advance of the knees via an increased dorsiflexion of the ankle. However, the tilt of the trunk will necessarily increase the shear forces in the lower back, and if the athlete is not strong enough, this could potentially lead to an injury.
In practice, competitors use special shoes for squat which have the particularity of having a rigid and raised sole at the heel (Fig. 1). These shoes aims to provide a stable base for the feet, but also increases the plantar flexion at the ankle. On the other hand, in gyms, many practitioners use running shoes to make their squat. These shoes are often criticized by the specialists because the cushioning of the sole does not allow such a stable support (and a good restitution of the forces on the ground) and an optimal security. What is the impact of these two types of shoes on the kinematics of the squat ?
Figure 2. Kinematic measurements (Click to enlarge)
To answer this question, a team of American researchers wanted to compare the kinematics of the squat with weightlifting shoes and running shoes. For this, they analyzed the squat of 25 participants (all university athletes and practitioners of resistance training since 5-7 years) under both conditions. The protocol consisted of performing a series of 5 repetitions at 60% 1RM in each condition. And repetitions 3 and 4 were used for analysis. Each series was filmed in profile and markers were placed at each joint and on the barbell for video analysis. The researchers observed the foot segment angle, the thigh segment angle, the anterior barbell displacement and the posterior hip displacement (ie, the trunk lean displacement) (Fig. 2).
The main results of this study show that weightlifting shoes allow a significant reduction in trunk lean displacement and a significant increase in the foot segment angle, compared to the wearing of running shoes. No difference was observed in the thigh segment angle (Table 1).
Despite the raised heel of the running shoe, the material that makes up the sole is not made to withstand compression, on the contrary. Thus, during a squat, even with moderate load, the sole will tend to crash under the constraints and therefore will not allow to maintain a plantar flexion angle similar to that observed with weightlifting shoes. The average difference observed here was 3.5 degrees.
This constant elevation of the heel results in a reduction in anterior tilt of the trunk during the squat. To balance the body, athletes must keep the trunk closer to the vertical. Moreover, the forward motion of the knees caused by the more pronounced inclination of the foot and the greater opening of the hip will tend to emphasize the work of the knee extensor muscles. It should also be noted that the thigh segment angle did not change according to the conditions. The parallel squat being reached at 0°, the subjects realized their squat with the same depth in both conditions, at about 20°. This means that with the weightlifting shoes, the practitioners did not go lower, which is unexpected.
This is the first study that compares weightlifting shoes with classic running shoes during a squat. In addition to providing a stable base for the support of the foot, the tilt caused by the heel causes a reduction in the anterior trunk displacement. This could reduce shear forces in the lower back and increase the mechanical efficiency during the concentric phase. In addition, an advantage of weightlifting shoes is to lower the squat lower thanks to the tilt of the foot more pronounced (and therefore a less need for dorsiflexion of the ankle). However, in this study, this was not the case. The study does not specify whether participants wore weightlifting shoes for the first time, which may have influenced the results, as their training usually involves going down to a specific depth.
For all the people not practicing in competition and not wishing to invest in a pair of weightlifting shoes, know that a greater mobility of ankle in dorsiflexion, feet flat on the ground, will also make it possible to advance a little more the knees, decrease the flexion angle of the knees and reduce the forward displacement of the trunk. Some methods work very well to improve ankle mobility (eg, mobilization with movement, self-myofascial release).
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