Acute Effects of Isometric Conditioning on Sprint, Jump and Change of Direction Performance in Youth Soccer Players

This study investigates the acute effects of an isometric conditioning activity on neuromuscular performance in elite youth soccer players. The study uses a randomized crossover design in which participants complete two experimental conditions in a randomized order.

Twelve male soccer players aged 15-19 years from a professional soccer academy competing in the Polish league system will be recruited. Eligible participants must have at least one year of resistance training experience, regularly participate in organized soccer and strength training and be free from neuromuscular or musculoskeletal disorders.

Each participant will complete two testing sessions separated by seven days. Each session will begin with a standardized warm-up consisting of cycling, dynamic mobility exercises and submaximal jumps. Baseline testing will include two countermovement jumps (CMJ), two drop jumps (DJ) from a 45-cm box, one maximal 30-m sprint and two 505 change-of-direction tests performed using the dominant and non-dominant leg.

Following baseline testing, participants will complete one of two conditions:

i) Isometric conditioning activity (experimental condition): unilateral standing isometric calf raises performed as 3 sets of 3 repetitions with a 3-second contraction for each repetition with a 3-minute rest period between sets.

ii) Control condition: low-intensity treadmill walking at 6 km·h-¹ for 9 minutes.

Seven minutes after completing the assigned condition, participants will repeat the performance tests to assess acute changes in neuromuscular performance.

Jump performance will be measured using a dual force plate system (Dual Force Plate System, CC Athletics, Denmark) sampling at 1000 Hz. Force-time data will be recorded and processed using the manufacturer's software according to standardized procedures. Linear sprint performance will be assessed using a 30-m sprint test performed from a two-point staggered start. Sprint time will be recorded using electronic timing gates (Witty Timing System, Microgate, Bolzano, Italy) positioned at 0, 5 and 30 m.

All testing will be conducted on a short indoor athletics runway located inside a gymnasium. The study aims to determine whether an isometric conditioning activity can acutely enhance explosive performance in youth soccer players and provide practical recommendations for warm-up strategies in soccer.

Inclusion criteria

• Male soccer players aged 14-19 years
• Currently participating in organized soccer training within a competitive soccer academy
• Minimum of one year of experience in resistance training
• Regular participation in both soccer training and resistance training for at least one year prior to the study
• Free from neuromuscular and musculoskeletal disorders that could affect performance

Exclusion criteria

• Presence of any current musculoskeletal injury affecting the lower limbs.
• History of neuromuscular disorders or medical conditions that could influence physical performance
• Any injury or health condition preventing maximal sprinting or jumping efforts during testing.