Ethics
The participants were informed orally about the procedures and all of them provided written informed consent. Informed consent from the next of kin, caretakers, or guardians on the behalf of the minors was obtained. The all experimental conditions conformed to the Declaration of Helsinki, and it was approved by the ethical committee of sport sciences research institute of University of Tehran, Iran (Code SSRI.REC-2201-1448).
The Consolidated Standards of Reporting Trials (CONSORT) guidelines were followed to ensure a high quality of reporting. This is a parallel-group randomized controlled trial. A total of 40 participants were selected and randomly assigned into 4 parallel groups. The UMIN Clinical Trials Registry approved the study protocol (Num: UMIN000050048, Date: 24/01/2023)
Participants
A sample size of 36 soccer player participants was calculated using G*Power software (version3.1.9.2; Kiel, Germany) based on the desired power of 80%, alpha of 0.05, and effect size of 0.6. Finally, forty adolescent professional soccer players with at least 3 years of regular soccer experience were included in the study to consider possible dropouts and randomly assigned to the intervention and control groups42. Assignment process is illustrated in the CONSORT diagram (Fig. 1). Demographic characteristics of the participants illustrated in Table 1.
The inclusion criteria were age ranged from 14 to 16 years old and they had all experienced at least 3 years’ regular soccer experience playing soccer at Tehran Youth Premier League. These players were employed by their clubs to participate in the premier league. The clubs had almost daily training and played one match per week in a season. The players of one team were randomly selected and assigned to one of the intervention programs. Exclusion criteria consisted of joint laxity (examining the individual Beaton index), neurological, no history of the trunk or lower limb surgery, fractures, and joint replacements of the lower extremity43. Goalkeepers were excluded from this study.
Procedure
The coaches and team managers from the four professional teams were invited to a four-hour instruction course that aimed to introduce the intervention programs. Before starting the intervention program, the coaches and club managers of the 4 groups were invited to an education course that was given by an experienced researcher which aimed to prescribe the warm-up intervention programs in detail (at the mid-season). All the coaches and participants of intervention groups received videos and illustrations of the 11+ program. All the training sessions were supervised and performed by the same study researcher to ensure their compliance with the programs. Verbal encouragement was given throughout the intervention period to motivate the players to concentrate on the quality of their exercise. All tests were conducted between 9:00 a.m. and 1:00 p.m.
Kinematic tests
Kinematic variables were measured using a Vicon motion analysis system (240Hz; MX Oxford Metric; Oxford, UK) with 6 cameras (T40s), VICON plug-in gait was used to process motion capture. In order to capture the cutting maneuver, 27 reflective markers (according to Plug-In Gait) were attached to bony landmarks of the lower limb. All Markers were attached with adhesive tape and straps directly to the participant's landmarks. All the markers were attached by the one of researchers. Kinematic data were filtered using a fourth-order zero-lag Butterworth 12-Hz low-pass filter automatically 44. The dominant leg of each participant was chosen by asking them which leg they would prefer for kicking the ball 45. The participant performed a general 10-minute warm-up with dynamic stretching concentrating on the lower body.
Before testing, each participant was shown the cutting maneuver and allowed to perform three test trials to familiarize themselves with the actual tests. Participants were allowed to rest for at least 5 min before testing. All participants wore indoor sports shoes. Regarding the cutting maneuver (Figure 2), the participant was instructed to run fast throughout 7-m until touching with their foot the area of the changing direction, and then perform the cutting. The range between the angles of 35° and 55° with respect to the initial path was found and marked using the marked ground and two cones on the floor, and players were instructed to perform the change of direction at the angle of 45° 46. Each participant performed three trials with one minute of rest between attempts and the mean of 3 attempts was used for the analysis. Tests were considered acceptable for each participant when there was no deceleration, wrong direction, losing balance, and perform movement patterns other than cutting
Joint Position Sense (JPS)
Knee and ankle JPS were measured by the use of a digital inclinometer by joint repositioning error methods. This method has been widely used and has been reported to have high reliability (ICC = 0.99)47. For this purpose, a digital inclinometer was attached to the middle third of the participants' shank of the dominant leg (the preferred leg for kicking a ball) with a hook-and-loop strap. For measuring ankle JPS, a digital inclinometer was attached to the participant's dominant leg foots with a strap The JPS was investigated at a target angle of 30°, 45°, and 60° knee flexion and at 20° of plantar flexion and dorsiflexion of the ankle. The participant was seated on the chair and actively flexed their knee and ankle to the target angle. The subject was asked to move his/her ankle or knee towards the target angle three times with his eyes open, and when he reached this angle, the examiner informed him/her and asked to keep his foot at that angle three times and keep it in his/her mind. Then, to eliminate visual and audible interferences during the measurement, the subject's eyes were blindfolded and wore headphones 10and he was asked to actively move his ankle and repositioned the target angle. The participant then held their knee and ankle at the target position for 5 s, and then returned to the starting position. The test was conducted three times, with 30 s of rest in between each test. We analyzed the difference between the target position and reproducing angle by the participants as the joint repositioning error. A lower mean error value indicates a better JPS.
The FIFA 11+ program
The FIFA 11+ has three parts with a total of 15 different exercises, performed within the indicated sequence at the begin of each training session rather than a regular warm-up program. Part one incorporates slow speed running exercises combined with active stretching and controlled partner contacts, the during part two exercise performed with focusing on core and leg strength, balance, and plyometrics exercise, players perform six sets of each exercises. Every exercise having three levels of increasing difficulty and this program in pat three ending with advanced running exercises (Table 2). The duration of FIFA 11+ in each session is approximately 20-25 minutes. In the current study the program was performed 3 times per week as a warm-up program for eight weeks under the supervision of the main researcher.
Control group
The control group was asked to use their usual warm-up routine and warm-up without any restrictions and follow their competition schedule.
Statistical analysis
SPSS software (IBM Corp, Armonk, NY) version 24 was used to analyze data. One-way analysis of variance was used to analyze the anthropometric parameters of the 4 groups at baseline. Shapiro-Wilk test, and Levene’s test were used to determine the normal distribution of data and homogeneity of variance, respectively. After did not confirm the homogeneity of regression slopes assumption of one-way ANCOVA, separate one-way ANOVAs between groups (male 11+ vs male control vs female 11+ vs female control) were used for each variable. In the case of statistical significance, the post-hoc Scheffe test was conducted. Effect sizes of each variable were tested using partial eta squared (pη2) values (small effect = 0.01, medium effect = 0.06, and large effect = 0.14) 48. For assessing the kinematic and JPS variables in every group (comparison of pre-test and post-test), the paired t-test was used. Moreover, the effect sizes for the two independent groups and the dependent t-tests were tested using Cohen’s d of [d = (M1 – M2 / √ ((SD1²×SD2²) / 2)] and [d = mean/SD], respectively (with 0.2, 0.5, and 0.8 considered as small, medium, and large effect sizes, respectively).