Considering the importance of an optimal warm-up to enhance performance in key soccer-related variables such as jump height, sprint speed, and ball kicking velocity, most available evidence to date has focused on youth and adult players, with limited studies conducted in children. Therefore, this study aimed to assess and compare the effects of a conventional warm-up and warm-ups including static stretching condition (SSC), dynamic stretching condition (DSC), and ball-specific condition (BSC) on jump performance countermovement jump (CMJ), squat jump (SJ), and drop jump (DJ) as well as on curve sprint speed, the Illinois change of direction test (ICODT), and ball kicking speed in male child soccer players. We hypothesized that the dynamic stretching warm-up would produce superior performance across most variables compared with the other conditions, due to its potential benefits for neuromuscular activation and optimization of the stretch shortening cycle.
Male children aged 8 - 13 years, enrolled in a soccer school affiliated with amateur clubs in Chile.
Regular participation in organized soccer training (≥2 sessions per week) for at least six months prior to the study.
Absence of musculoskeletal or neurological injuries that could limit the ability to perform the warm-up or physical performance assessments.
Availability of appropriate sports clothing and footwear for testing sessions.
Sustain an injury or illness during the study period that prevents participation in testing.
Fail to complete all four experimental conditions or physical assessments.
Demonstrate non-compliance with the warm-up instructions or assessment procedures.
Crossover
conventional warm-up regarding to stretching warm-up
Other interventionThe warm-up protocol was based on the guidelines of a previous study conducted on adolescent players in Chile. The CC performed a traditional soccer warm-up for 10 minutes, consisting of 4 minutes of jogging in different directions at moderate to vigorous intensities, measured using the 10-point perceived exertion scale (RPE) scale, starting between 3 and 5 points and ending between 6 and 8 points, followed by movements performed in matches (jumps, ball kicks, changes of direction) distributed in three sets of 60 seconds each with a 60-second rest between sets. This condition did not include flexibility exercises. The SSC consisted of a warm-up with static stretching for 10 minutes. Four stretching exercises were performed, one for each lower body muscle group (quadriceps, glutes, hamstrings, and triceps surae), distributed in two sets of 30 seconds each with a 45-second rest per exercise, performing progressive increases in joint range of
Bipedal height
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
Body mass
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).
Jump performance
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-
Curve sprint speed
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
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