Conventional Warm-up on Physical Performance in Children Soccer Players

Primary outcomes

1. Bipedal height

   Time frame: 8 Weeks

   Bipedal height was measured using the Frankfort plane in a horizontal position, with a tape measure (Bodymeter 206, SECA, Germany; accuracy to 0.1 cm) attached to the wall

2. Body mass

   Time frame: 8 weeks

   Body mass was measured using an electronic scale (Omron HBF 514, Osaka, Japón; accuracy to 0.1 kg), while BMI was calculated by dividing body mass by bipedal height squared (kg/m2).

3. Jump performance

   Time frame: 8 weeks

   All jump tests were performed according to previous recommendations. For the CMJ, soccer players performed maximum effort jumps on an Ergojump® Globus mobile contact platform (ErgoTest, Codogne, Italy) with their arms resting on their iliac crests. Takeoff and landing were standardized at the exact location, and players performed full knee and ankle extensions during the flight phase. For the SJ, players stepped onto the contact platform with their arms on the iliac crest and knees semi-flexed at a 90° angle and the "stop" signal; the player maintained this posterior position, performing the maximum jump. Takeoff and landing were standardized at the exact location, and players performed full knee and ankle extensions during the flight phase. In the DJ test, participants were instructed to minimize ground contact time (<250 ms) after stepping off a 20 cm box. The best of three jumps (with a 1-

4. Curve sprint speed

   Time frame: 8 weeks

   Sprint time was assessed to the nearest 0.01s using single-beam timing gates Brower® Timing System, (Salt Lake City, Utah, United States of America). The test consisted of placing a "semicircle" at a distance of 17 m outside the large area of the soccer field, which is standardized as follows: a radius of 9.15 m from the penalty spot, a distance of 14.6 m from the starting point to the end in a straight line, an angle of 105.84° measured from the penalty spot, and a total distance of 17 m (determined by trigonometric analysis). Photocells were installed at both ends of the semicircle to determine the time it took the players to run the curve. The test started from the left side, and the participant had to run at maximum speed until crossing the finish line. Two attempts were evaluated in both directions of the curve (left and right), recording the results as "dominant side" and "non-dominant side," depending on the dominance of the children soccer player's lower

5. Agility

   Time frame: 8 weeks

   The dimensions and route markings for the Illinois Change of Direction Test (ICODT) were adjusted to established methods. The ICODT consists of placing four markers to indicate an area of 10 m by 5 m. In the center of the area, four markers are placed at 3.3 m from each other. The children soccer players start in a prone position with their chin touching the surface of the starting line. They accelerate for 10 m, turn around, return to the starting line, zigzag in and out of the four markers, and finally complete a second 10 m sprint to finish the ICODT speed test. Players were instructed to run around the markers rather than cross them. If a participant did not follow these instructions, the test was terminated and restarted after a 3-minute recovery period. Performance results were collected using Brower® Timing System single-beam timing gates (Salt Lake City, Utah, United States of America).

6. Ball kicking speed

   Time frame: 8 weeks

   Participants performed a maximal instep ball strike with their dominant and non-dominant legs after a two-stride run using a size five soccer ball (Molten Vantaggio 5000®, FIFA PRO certified, Hiroshima). Maximum speed was measured with a radar gun Speed (Gun SR3600, Sports Radar®, Homosassa, Florida, United States of America). Three attempts were carried out, recording the best of the three with a 1-min rest between each attempt. The data obtained for ball kicking speed was determined to have high reliability of 0.92.