Effects of a Plyometric Training Program on Youths With Different Biological Maturity in Sport

The vertical jump is performed on AMTI OR6-7-1000 force platform (Advanced Mechanical Technology, Watertown, USA). Participants stand on the force platform in an upright position and on command, perform a maximum height jump with a countermovement and use of arms. Participants perform three attempts, with a 1-min rest between each. The best attempt is evaluated.

The distance in the broad jump is measured with a tape. Participants stand on a pre-marked line with legs approximately shoulder-width apart. From standing, they jump as far forward as possible using a countermovement and land on both feet. The landing spot closest to the starting line is considered for scoring. Participants perform two attempts, with the better attempt being recorded. There is a 1-min rest between attempts.

The length of the unilateral triple jump test is measured with a tape. Participants start on one leg on a pre-marked line. Then using a countermovement from knee flexion, they perform a triple jump with the dominant and subsequently the non-dominant lower limb. After the final jump, they must land on both limbs and maintain their position at the landing spot for at least 2 seconds.

A 20-m sprint test is used to assess linear speed. The final time is recorded using photoelectric cells (Brower Timing System, Draper, USA) with accuracy of 0.01 s. Photocells are placed at the start and 20-m mark. Participants start on command, with timing starting as soon as the player begins to move.

For the 505 agility test, photoelectric cells (PR1aW, ALGE-TIMING, Lustenau, Austria) are used, placed at the 10-m mark. Cones are placed at the 0, 10, and 15-m marks. Participants sprint 10 meters and are instructed to reach maximum speed by the 10-m mark. At the 15-m mark, they perform a 180-degree turn and sprint back to the 10-m mark at maximum speed. Each participant have one attempt on the dominant and one attempt on the non-dominant leg for the 180-degree turn.

In the BlazePod reaction test (Play Coyotta, Tel Aviv, Israel), 5 sensors are placed parallel, 1 m apart from each other. The participant stand 3 m in front of the middle sensor. When any sensor lights up, the participant must press it as quickly as possible and return to the starting position, waiting for the next sensor to light up. Sensors light up in a random order. The test lasts after 10 attempts.

Lower limb stiffness is measured using the repeated submaximal jumps test (Optojump Next, Microgate, Italy). Participants perform 20 repeated jumps at a frequency of 2.5 Hz (mechanical metronome Wittner, Isny, Germany). Participants stand approximately shoulder-width apart with their hands on their sides throughout the test. Participants undergo three attempts with 2-min rest in between.

Reactive strength index is measured using the drop jump on AMTI OR6-7-1000 force platform (Advanced Mechanical Technology, Watertown, USA). Participants stand with feet shoulder-width apart on a platform 30 cm above the floor and have their hands on their sides. Then they step off the platform with one foot and upon landing, rebound as quickly as possible and with maximum effort. Reactive strength index is calculated from the ratio of jump height to the duration of contact with the platform.