Effectiveness of Recovery Protocols in Elite Professional Young Soccer Players

Counter Movement Jump (CMJ) will be performed to determine the maximum height in centimeters (cm). From standing position with the hands fixed on the hips, participants will be required to bend their knees to a freely chosen angle and perform a maximal vertical jump. Participants will be instructed to keep their body vertical throughout the jump, and to land with knees fully extended. Any jump that will be perceived to deviate from the required instructions will be repeated. Players will jump 3 times as high as possible and the average of the three jumps will be used in subsequent analysis. A 30-s passive recovery phase will be provided between jumps.

Isometric Hamstring Strength (IHS). Players will be in a supine position, with the tested leg strapped around the ankle (in a neutral position) and performed a hip extension (with a slight knee flexion 20º, while the non-dominant leg was resting on the floor). Players will place their hands on the wall to avoid sliding on the floor. A strain gauge will be placed between the ankle strap and the cord to evaluate the force (MVIC) exerted at a sampling frequency of 80Hz (Chronojump, Boscosystem®️, Barcelona, Spain).

The tester will give all participants the same instructions; "to exert maximal force down to the floor" and continuous and standardized verbal motivation for 5 seconds. Each limb will be tested 3 times, in a randomized order. The assessment of both legs will be separated by 30 seconds while the time separating two trials of the same leg will be 60 seconds . The MVIC will be tested and measured in Newtons (N).

Creatine Kinase (CK): units/L

Mioglobin: n/mol/L

Urea: umol/L or mg/dL

Na and K ions: mmol/L

Internal rotation of the hip test will be performed to determine the maximum rotation (º) degrees of this joint. Players will lie down (prone position), with legs stretched out. They will put their leg at 90 degrees and allow that leg to flop out to the side, making sure to keep the opposite hip firmly on the ground. From here, the angle that their leg can rest outward will be assessed. It will be performed and recorded two times for each leg and the average will be used.

Ankle dorsiflexion test will be performed to determine the maximum range of movement of this joint. This test needs to be done against a wall. Players will be asked to place their foot in a way that an imaginary line drawn through the heel and big toe will be aligned on the tape measure on the floor. Players will be instructed to lunge forward until their knee touches the wall. The heel will be required to remain in contact with the floor at all times. The foot will be moved away from the wall to the point where the knee will only make slight contact with the wall. The leg not being tested will rest on the floor and participants won't be allowed to hold onto the wall for support. The dorsiflexion range of movement will be measured in degrees (º) and the average of two attempts will be used.

Active Straight Leg Raise (ASLR) test will be performed to determine the maximum extension (º) degrees of this muscle group. Players will lie down (supine position), with the knees over the mat. Once positioned, the players will be asked to slowly raise their limb with the knee fully extended and the ankle in maximal dorsiflexion. During the test, the non-tested limb will keep on the mat, with the ankle in maximum dorsiflexion and the head on the ground. When the maximum ROM will be reached, the angle that their leg will achieve will be assessed. It will be performed and recorded two times for each leg and the average of two attempts will be used.

Jurdan Test will be performed. Initially, the player will be in supine in a similar position to the modified Thomas test but will be asked to complete an active knee extension (holding the thigh at 90°) while holding the table and holding the lumbar spine in contact with the table. The lumbar position will be verified kinaesthetically by the practitioner in the starting position and visually during execution. Maintenance of the thigh angle at around 90° for the active knee extension during testing will be visually verified. The result will be defined as the difference between the actively lengthened legs shin angle and the opposite legs passive thigh angle (which is hanging over the table's edge). Both angles (º degrees) will be measured relative to horizontal. It will be performed and recorded two times for each leg and the average of the two attempts will be used.

The questionnaire (McLean et al. 2010) will assess participants' fatigue, sleep quality, general muscle soreness, stress levels and mood on a five-point scale (scores of 1 to 5, 0.5 point increments, being 5 the best state and 0 the worst). Overall well-being will then be determined by summing the five scores.

Total Quality Recovery Perceived (TQRper) using a 10 point Borg scale (being 0 extremely tired/very poorly recovered and 10 highly energetic/very well recovered) will also be recorded.

Rate of Perceived Exertion (RPE) using the Foster 0-10 scale (being 0 no exertion and 10 maximal exertion) will also be recorded. Players will respond one simple question: How hard was your session? Each player will complete the 0-to-10 scale without the presence of other players and will not see the values of other participants. Players will be allowed to mark a plus sign (interpreted as 0.5 point) alongside the integer value