Table 2 The structured warm-up program used in the intervention group

1. One-legged knee squat

Slow movement with a smooth turn. Keep the pelvis in a horizontal position. Non-supporting foot held in front of the body with slightly flexed hip and knee.

   Level A

Hands on the hips.

3 × 8–15

   Level B

Hold a ball over the head with straight arms.

3 × 8–15

   Level C

Hands on the hips. Mark with the non-supporting foot just above the ground at the 12-02-04-06 o'clock positions.

3 × 5

   Level D

Bend down while holding a ball and let the ball touch the ground outside the supporting foot. Make a diagonal movement upwards and raise the ball over the head with straight arms on the contralateral side.

3 × 8–15

   Pair-exercise

Teammate stands slightly oblique in front of you. Hands on the hips and press a ball between the lateral sides of the feet of the non-supporting legs.

3 × 5–10

2. Pelvic lift

Supine position. Lift the pelvis from the ground while keeping the back straight.

   Level A

Both feet on the ground and hands across the chest.

3 × 8–15

   Level B

One foot on the ground and the contralateral leg flexed in the hip and knee approximately 90 degrees with both hands on the knee.

3 × 8–15

   Level C

One foot on a football and the contralateral leg flexed in the hip and knee approximately 90 degrees with the arms on the ground alongside the body for support.

3 × 8–15

   Level D

One foot on the ground and the other in the air. Keep the upper arms on the ground for support with the elbows flexed 90 degrees. Push away the supporting foot and land on the contralateral foot.

3 × 8–15

   Pair-exercise

Teammate stands with flexed knees and supports the heel of one of your feet in her hands. Hands across the chest and lift the pelvis.

3 × 8–15

3. Two-legged knee squat

Slow movement with a smooth turn. Keep the back in a straight position. Feet shoulder-wide apart with the soles in contact with the ground at all times during the squat.

   Level A

Hold a ball in front of the body with straight arms.

3 × 8–15

   Level B

Hands on the hips.

3 × 8–15

   Level C

Hold a ball over the head with straight arms.

3 × 8–15

   Level D

Same as Level C, but continue the movement and rise up on the toes after returning to the starting position. Stay briefly in that position with good control.

3 × 8–15

   Pair-exercise

Teammate stands next to you approximately 1 meter away, face opposite directions. Hold a ball between you with one hand and the other hand on the hip. Apply slight pressure on the ball while performing the knee squat.

3 × 8–15

4. The bench

Lift the body and keep it in a straight line.

   Level A

Prone position. Support on the knees and on the lower arms with the elbows kept under the shoulders.

15–30 seconds

   Level B

Same as Level A but with support on the tip of the feet.

15–30 seconds

   Level C

Same as Level B, but move the foot to the side and back to the starting position. Alternate sides.

15–30 seconds

   Level D

Lie sideways with support on the foot and the lower arm with the elbow kept under the shoulder and the other hand on the hip. Lift the hip off the ground and stay briefly in that position with good control before slowly returning to the starting position.

3 × 5–10

   Pair-exercise

Teammate stands behind you and holds your feet or lower legs. Lift the body and walk forward by using the hands on the ground.

15–30 seconds

5. The lunge

Take a step with a marked knee lift and a soft landing.

   Level A

Hands on the hips. Move forward with each step.

3 × 8–15

   Level B

Hold a ball in front of the body with straight arms. Rotate the upper body while stepping forward and position the ball laterally of the front leg. Move forward with each step and alternate sides.

3 × 8–15

   Level C

Hold a ball over the head with straight arms. Perform a forward lunge and push back with the front leg and return to the starting position.

3 × 8–15

   Level D

Hold a ball in front of the body with straight arms. Perform a sideway lunge and return to the starting position.

3 × 8–15

   Pair-exercise

Teammate stands in front of you 5–10 meters away. Perform a forward lunge while making a throw-in with a ball.

3 × 8–15

6. Jump/landing

Make a jump with a soft landing. Stay briefly in the landing position.

   Level A

Stand on one leg with the knee slightly bent and hands on the hips. Make a short forward jump and land on the same foot. Jump backwards to the starting position.

3 × 8–15

   Level B

Stand on two legs shoulder-wide apart with the hands on the back. Make a sideways jump and land on one foot. Alternate sides.

3 × 8–15

   Level C

Take a few quick steps on the same spot and make a short jump straight forward landing on one foot.

3 × 5

   Level D

Same as level C, but change direction and jump to one side (90 degrees turn). Alternate sides.

3 × 5

   Pair-exercise

Teammate stands in front of you approximately 5 meters away. Make a two-legged jump while heading a football and land on two legs.

3 × 8–15