EFFECT OF PREPARATORY POSTURE ON PERFORMANCE IN LATERAL DIVES

The Goalkeeper preparatory body posture for a defensive action, also known as Set, Pre-action, Basic, Base or Initial position, is a dynamic posture, adaptable to the circumstances posed by the game that promotes muscle pre-activation. In this position, the legs are semi-flexed and the feet are separated to create a good support surface. But how bent should the legs be and how far apart should the feet be to achieve the best performance in diving? In a study published in 2019, researchers from the Department of Human Movement Sciences at the University of Vrije and the Adidas MiCoach Performance Center in the Netherlands tried to identify the optimal values of these two variables in the preparatory posture.

As in another article by the same authors that we previously reported (http://cefarq.com.ar/en/incidence-of-the-contralateral-leg-push-for-side-dives/), ten goalkeepers aged 16 to 20, who play at the highest levels of competition in the Netherlands, participated in the experience. The researchers sought to measure the effect of different leg spacing widths and knee flexion angles on the trajectory of the center of mass and velocity in the goalkeeper’s dives. Using infrared cameras, they recorded trajectory data from 44 markers on their bodies, during high and low lateral dives (http://cefarq.com.ar/en/lateral-dives/) to static balls hunging at 190 and 30 cm high respectively. Using force platforms, they measured the ground reaction forces produced by each leg. They initially recorded the values ​​for dives in which the goalkeepers started from their preferred preparatory postures. Then they imposed postures with certain values ​​of knee flexion and leg separation. For the flexion they chose values ​​of 45°, 75° and 90°; for the separation they used standardized distances of 50%, 75% and 100% of the goalkeeper’s leg length. When they manipulated the flexion, the separation was left to the choice of the goalkeepers and vice versa. Finally, the goalkeepers executed dives choosing their preferred posture again.

Preparatory Posture. The sum of the segments A + B defines the length of the leg by which the width of the spacing D is normalized. C indicates the angle of flexion of the legs.

Statistical analyzes showed that the best performances, in terms of dive speed, distance traveled by the center of mass and more direct displacement towards the ball, occurred when the goalkeepers adopted a preparatory posture with a flexion angle of approximately 55 ° (the preferred by goalkeepers) and a leg separation equal to 75% of the length of their legs (wider than preferred by goalkeepers). The researchers claim that, although their interpretations are well supported statistically, verification of the observations in other populations of goalkeepers is needed to arrive at a more definitive generalization of the results.

Another important aspect noted by the researchers is the limited ecological validity of the experience, since the game situations not only include dives from a certain preparatory posture and the movement time is not the only variable that determines the performance of the goalkeepers (http://cefarq.com.ar/la-palabra-del-df-director-fundador-4/). Instead, they understand that the test used is close to real game situations in set pieces (such as penalties and direct free kicks), and some open play situations in which goalkeepers have enough time to get into a preparatory stance.