The Impact of Blood Flow Restriction Within Warm-up.

Sixty athletes will be randomized in two groups; (1) an experimental group and (2) a control group. Both groups will undergo the following procedure:

Moment 1:

1. Baseline testing: countermovement jump, 25m sprint and strength assessment of the Hamstrings and Quadriceps muscle.
2. Short warm-up (approximately 4 minutes), which will be completed with blood flow restriction cuffs (experimental group) or without (control group)
3. Post testing: same tests as performed in baseline.

Moment 2:

1. Baseline testing: stiffness measurements of the Biceps Femoris Long Head via Shear Wave Elastography.
2. Short warm-up (approximately 4 minutes), which will be completed with blood flow restriction cuffs (experimental group) or without (control group)
3. Post testing: same tests as performed in baseline.

Both moments of testing as well as the order in which the performance tests take place are randomized.

Traditionally, athletes perform a warm-up program before participating in sport activities, due to its assumed beneficial effect on performance and injury prevention. However, within team sports, substitutes usually do not perform the comprehensive pre-match warm-up. In many cases, those substitute players get a very short period of time, during the game, to prepare themselves for coming on to the pitch where they immediately have to perform at a very high-intensity. Hence, this could lead to a poorer performance and a greater injury risk for those substitute players, as they did not get a decent warm-up.

Therefore, new techniques are needed in order to prepare the substitute athletes optimally in a very short period of time (often within a few minutes). Consequently, the aim of this study is to investigate whether the incorporation of Blood Flow Restriction (BFR) within a warm-up routine could be of additional value. Both performance parameters and muscle stiffness will be evaluated. As Hamstring strain Injuries (HSI) are common within sports encompassing high-speed running, this muscle group will be investigated on muscle stiffness as a representation of the interventional effect on muscle stiffness. Athletes will be randomized in two groups of 30 participants (anticipated); (1) an experimental group and (2) a control group. Both groups will perform baseline testing (5x Countermovement Jump, 25m Sprint and Muscle Strength of hamstrings and Quadriceps), and a short warm-up program, followed by repeating the same tests as executed in baseline. The experimental group will receive Blood Flow Restriction within the warm-up routine, whereas the control group will do the same warm up program but without BFR.

On a separate occasion, the same athletes will perform the same warm-up routine with a Shear Wave Elastographic assessment of the Biceps Femoris Long Head before and after (immediately after, after 5 minutes and once more after 10 minutes) the warm-up.

Eligibility Criteria:
Inclusion Criteria:

* Free of pain at the moment of testing
* Adult (18+)
* Athletes (competitive team sport)

Exclusion Criteria:

* History of a hamstring strain injury
* History of cardiovascular problems
* Recent (\<1 year) trauma or surgery of the lower extremity
* Reduced functioning or pain in the lower extremity.
* Not being able to perform physical activities, for whatever (medical) reason.