Eccentric and Trunk Stability Exercise Program Effects in Young Soccer Players

Study Overview
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Brief Summary
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The purpose of the present study is to investigate the effects of an in-season mixed training program on several physiological parameters of soccer players. Twenty-one U19 elite soccer players recruited and randomly assigned to either an 8-week specific training experimental group or a control group. The program will include an eccentric hamstring exercise, static balance exercises and core muscles strengthening exercises. Isokinetic hamstring and quadriceps strength, single leg static balance and lumbopelvic stability will be measured prior and after the intervention.

Detailed Description
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A total of 123 male Under-19 (U19) players from several soccer teams were initially invited for participation in the study after signing informed consent forms. following a second contact with the participants, questionnaire forms with inclusion and exclusion criteria were send for completion. Based on their self-report and a clinical examination by a health professional, of the 103 players, 42 did not meet the inclusion criteria, while 12 players did not participate for personal reasons. Of the remaining 69 players, 48 players were excluded, including 3 players reporting an anterior cruciate ligament reconstruction, 14 because of lower extremity injury led to more than two weeks absence from training and 10 players because of secondary injuries or health problems that led to loss of training the past 3 months. A neutral, blinded investigator with no further involvement in the study was responsible for randomized allocation of participants in two groups. All training sessions in the training group will be supervised by a fitness coach, who will ensure that the exercises are performed according to protocol.

Official Title
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Effects of an 8-week Eccentric and Trunk Stability Exercise Program on Muscle Strength and Postural Stability in U19 Elite Soccer Players

Conditions
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Muscle Strength, Postural Balance

Intervention / Treatment
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* Other: Sliding leg curl
* Other: Balance training
* Other: Core stability


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: 16 to 19 years old soccer players Trained at least 3 times and played 1 match weekly, the past 4 years Healthy Free from muscle injuries in the 6 months prior to the study Exclusion Criteria: History of anterior cruciate ligament rupture History of ankle, hip or knee injury with duration at least 1 week, in the 3 months prior to the study Muscle injury with duration at least 1 week, in the 3 months prior to the study Any reason resulting in 2 weeks loss of training the preceding 6 months Involvement in hamstring strengthening, core stability or balance training program in the 6 months prior to the study

Ages Eligible for Study
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Minimum Age: 16 Years
Maximum Age: 19 Years

Sexes Eligible for Study
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Male

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Allocation: Randomized
Intervention Model: Parallel Assignment
Masking: Double


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Training group<br>For the balance exercise the participants will perform one-legged stance of certain duration, on a stable surface. For the sliding leg curl exercise the participants lay supine on a mat, wearing only socks in order to create a slippery surface between their heels and the gym floor. The player begins by extending the hip and having the working leg on knee flexion. The contralateral limb is on hip flexion and knee flexion. The base of support is the shoulder blades, the elbows and the heel of the working leg. After assuming this position, the player begins to extend the knee, as slowly as possible, resisting the low friction properties of the ground. The core stability program consists of front plank, side planks, supine bridge, leg lowering and superman exercise. These exercises will be performed at the end of the training session, in contrast to the balance and hamstring exercises which will be executed before the training session. | Other: Sliding leg curl<br>* The exercise protocol consists of the following sets and repetitions Week 1- 2 sessions with 2 sets of 6 repetitions Week 2- 2 sessions with 3 sets of 6 repetitions Week 3- 2 sessions with 4 sets of 6 repetitions Week 4- 2 sessions with 4 sets of 8 repetitions Week 5- 2 sessions with 4 sets of 10 repetitions Week 6- 2 sessions with 4 sets of 10 repetitions Week 7- 2 sessions with 4 sets of 8 repetitions Week 8- 2 sessions with 4 sets of 8 repetitions<br>Other: Balance training<br>* The exercise protocol consists of 2 sessions/week with 4 sets of 30'' single stance. Week 1 and 2- 1 set of 30'' single leg stance and 3 sets of 30'' single leg stance and ball kicks with contralateral foot Week 3 and 4- 2 sets of 30'' single leg stance while moving the ball around the leg with the contralateral foot and 2 sets of 30'' single leg stance, moving a ball around the knee with hands and kicking a ball with contralateral foot Week 5 and 6- 2 sets of 30'' single leg stance while giving and receiving hand passes with medicine ball (in couples) and 2 sets of 30'' single leg stance with perturbations (in couples) Week 7 and 8- Same as week 5 and 6 with extra 15 in each repetition<br>Other: Core stability<br>* The exercise protocol consists of the following sets and repetitions Week 1 and 2- 3 sets of 30'' front plank, 3 sets of 20'' side plank, 2 sets of 30'' superman, 2 sets of 30'' supine bridge and 2 sets of 10 repetitions leg lowering exercise Week 3 and 4- increasing difficulty in 2 of the sets Week 5 and 6- adding 1 more set at each exercise Week 7 and 8- adding 15 in each repetition<br>|
| No Intervention: Control group<br>The participants in this group will follow only the usual training program | |

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Peak concentric and eccentric torque of hamstrings and quadriceps | Peak torque (N.m) is measured using isokinetic dynamometer at each angular velocity (30°·s-1, 180°·s-1, 240°·s-1). | Change from baseline assessment at 8 weeks | 
| Total sway of the center of pressure (CoP) | This is defined as the average distance (mm) of the CoP from the reference lines and the amplitude is its standard deviation | Change from baseline assessment at 8 weeks | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Angle at peak torque of hamstrings and quadriceps | The angle at which peak torque of hamstrings and quadriceps muscles was achieved, at each angular velocity, measured in degrees (°) | Change from baseline assessment at 8 weeks | 
| Conventional hamstrings to quadriceps ratio | This is calculated by dividing peak isokinetic concentric hamstring strength by the peak isokinetic concentric quadriceps strength, at the same angular velocity | Change from baseline assessment at 8 weeks | 
| Dynamic hamstrings to quadriceps ratio | This is calculated by dividing peak isokinetic eccentric hamstring strength by the peak isokinetic concentric quadriceps strength, at the same angular velocity | Change from baseline assessment at 8 weeks | 
| Mixed hamstrings to quadriceps ratio | This is calculated by dividing peak isokinetic eccentric hamstring strength at 30°·s-1 by the peak isokinetic concentric quadriceps strength at 240°·s-1 | Change from baseline assessment at 8 weeks | 
| Average speed of CoP | This reflects the amplitude and frequency of CoP movements and is calculated as the total length of the path of CoP divided by the test trial time (mm·s-1 ) | Change from baseline assessment at 8 weeks |