Velocity-Based vs Percentage-Based Strength Training in Young Football Players

In the countermovement jump (CMJ) test, vertical jump height was measured using an Infinitek electronic vertical jump device (Infinitek Company, Istanbul, Turkey). Each participant performed two trials, separated by a 60-second passive rest interval. The better performance was recorded for analysis.

A wireless two-door Sinar photocell device (Sinar, Turkey) was used to measure 20-meter sprint performance. Each participant performed two 20-meter sprints, separated by a three-minute rest interval, and the better time was recorded. Participants were instructed to walk forward naturally with relaxed arms and an upright posture beginning three meters before the timing line. After the final step before the line, they accelerated maximally through the 20-meter distance.

Aerobic capacity was assessed using the Yo-Yo Intermittent Recovery Test Level 2 (Yo-Yo IR2). In this test, participants performed repeated 2 × 20-meter shuttle runs at progressively increasing speeds, moving back and forth between the starting, turning, and finishing lines. Between each shuttle run, a 10-second active recovery period was allowed, during which participants walked or jogged within a 5-meter recovery zone. Running speed was dictated by audio signals automatically controlled by a CD player. Cones were used to mark 2-meter-wide, 20-meter-long running lanes, with an additional cone placed 5 meters behind the starting line to indicate the recovery area.The test was terminated when the participant was unable to continue or failed to reach the finish line on two consecutive occasions. The total distance covered was recorded as the test result. Maximal oxygen uptake was estimated using the following equation: VO2max = distance (m) × 0.0136 + 45.3

In the TRD group, the one-repetition maximum (1-RM) squat was determined using the traditional percentage-based method. Before the athletes began the test, the coach selected an appropriate starting weight for each participant. Athletes were advised to begin with lower loads to ensure proper anatomical positioning and technique before progressing to heavier weights.

In the VBT group, the one-repetition maximum (1-RM) squat was measured weekly using an Apple iPhone 7 Plus (iOS 12.4.1; Apple Inc., USA) with the My Lift application (My Jump Lab, Spain). Before beginning the exercise, participants received a verbal command to initiate the movement. The squat exercise was uploaded to the device and recorded. The range of motion during the squat was measured in meters. For standardization, participants were instructed to squat until reaching 90° of knee flexion and then immediately return to the starting position with full extension of the knee and hip joints.

In the VBT group, the one-repetition maximum (1-RM) bench press was measured weekly using an Apple iPhone 7 Plus (iOS 12.4.1; Apple Inc., USA) with the My Lift application (My Jump Lab, Spain). Before beginning the exercise, participants received a verbal command to initiate the movement. The bench press exercise was uploaded to the device and recorded. The range of motion during the bench press was measured in meters. For standardization, participants were instructed to lower the bar to the chest and then immediately return to the starting position with full elbow extension. Prior to initiating the speed-based strength training measurement, the distance from the center of the bar to the participant's chest was measured and entered into the My Lift application as required.