The Effect of 6 Weeks Supplemental Jump Training on Sand Versus Hard Surfaces on Landing Knee Valgus and Jump Performance in Adolescent Female Football Players

Participants will be under 16 females currently training and playing for the football Emerging Talent Centre (ETC) at Teesside University.

The testing will take place at Teesside University. Participants will attend on 2 occasions (Pre and post intervention). During the first session participants age, height, and weight, will be collected. Participants will then perform a warmup consisting of fundamental movements like squatting, lunging, running, skipping and jumping.

Participants will then be asked to perform 5 practice trials of a single leg step landing task from a 30cm box. This will be demonstrated to them initially and then the practice trials will allow participants a chance to orient themselves to the task before data collection. For the step down task participants will be instructed to stand on the box and then step off the box and land and hold the position on their dominant leg (which is decided by the leg they prefer to kick a ball with).

Throughout testing participants will be required to wear reflective markers (14mm) over dark coloured shorts and top. The markers will be attached with double sided adhesive tape to the participants lower extremities over the following landmarks: anterior superior iliac spine (left and right), mid tibiofemoral joint (left and right) and mid talocrural joint (left and right). The same individual (MR) will place the markers on all participants. Midpoint will be determined using a standard tape measure. These markers will be used to calculate a knee angle on landing (specific outcome measure detailed elsewhere), measured using a high speed digital video camera (Quintic GigE 1mp; Quintic Consultancy Ltd, West Midlands, United Kingdom) recording at 200 frames per second, positioned 2 m anterior to the subjects' landing target at the height of the participant's knee and aligned perpendicular to the frontal plane. Images captured will be imported into a digitizing software program (Quintic 29; Quintic Consultancy Ltd) ready for analysis. The average landing value from 5 trials during the task will be used for analysis.

Following completion of the step-down task participants will then be asked to complete two performance tests (with a standardised 3 minute rest period between them). As within the step landing task they will be given practice trials to help familiarise themselves with the tests prior to data collection. The first test with be a countermovement jump (CMJ), where participants will stand on a force platform (built into the laboratory floor). Each foot will be on an individual force plate. Participants will then be asked to squat down, keeping their hands on their hips and subsequently jump as high as they can. Whilst in flight they must keep their hands on their hips and keep their leg straight. Participants will be instructed to land in the same position they took off from (i.e. not forward or backwards). Tape will be stuck on the floor as a marker to help guide the participants towards achieving this. The participant will perform 3 efforts with the average height being used for analysis. The second test is the 10/5 repeated jump test to evaluate the participants reactive strength index. The test requires the participant to execute 10 maximal rebound jumps (attempting to minimise ground contact time between jumps). Of the 10 jumps, the 5 that display the greatest jump height are used for analysis. The 10/5 test will be measured using the same in-ground force plate noted for the CMJ test. As with the CMJ test participants will be instructed to keep their hands on their hips throughout the jump phase and each of the 10 repeated jumps. One trial of the test is all that is required for data analysis purposes.