The purpose of this 8-week periodized field study is to investigate and compare the acute and chronic effects of three different sled towing loads (10%, 15%, and 20% of body weight \[BW\]) on sprint performance (5m, 10m, 15m) and neuromuscular characteristics (Squat Jump \[SJ\], Countermovement Jump \[CMJ\], Drop Jump \[DJ\], and Reactive Strength Index \[RSI\]) in trained male youth football players aged 13-14 years. While all other training variables (distance, frequency, volume, and rest intervals) are standardized, this study aims to identify the optimal sled load that enhances acceleration and horizontal force production without compromising running mechanics during a critical pediatric athletic development window.
Background and Rationale: Sprint performance, acceleration capacity, and change of direction speed are key determinants of athletic success in association football. The age period of 13-14 years represents a "critical window of opportunity" characterized by rapid adaptations in neuromuscular control, motor unit recruitment, and myelination. Resisted sprint methods, particularly sled towing, allow athletes to overload horizontal force production at sprint-specific joint angles without altering overall running kinematics. However, there is a methodological gap in the literature regarding the optimal and safe acute load prescription (%BW) for pediatric and youth populations. Study Design and Methodology: This study is an 8-week, parallel-group randomized controlled field trial involving 30 licensed male youth football players. Participants are randomly allocated into three homogeneous intervention groups using a stratified block randomization method based on baseline 15-meter sprint performance: Light Load Group: Sled towing with 10% Body Weight (BW) Moderate Load Group: Sled towing with 15% Body Weight (BW) Heavy Load Group: Sled towing with 20% Body Weight (BW) Training Protocol: Sled sprint training sessions will be conducted twice per week (minimum 48 hours of recovery between sessions) over 8 weeks (16 total sessions) at the beginning of regular football practice, immediately following a standardized 15-18 minute warm-up protocol. Running distance (15 meters per repetition), inter-repetition rest (2 minutes), and inter-set rest (3 minutes) will be held constant across all groups. Training progression will be achieved through gradual volume increases: Weeks 1-2: 2 sets × 3 reps (90 m/session) Weeks 3-4: 2 sets × 4 reps (120 m/session) Weeks 5-6: 3 sets × 3 reps (135 m/session) Weeks 7-8: 3 sets × 4 reps (180 m/session) Outcome Assessments: Baseline (pre-test) and post-intervention (post-test) evaluations will be conducted on non-fatigued days. Primary outcome measures include: Sprint Performance: Linear sprint times over 5m, 10m, and 15m measured using a high-precision wireless photocell timing system. Neuromuscular Performance: Vertical jump heights (cm) assessed via Squat Jump (SJ) and Countermovement Jump (CMJ) tests on a digital contact mat/force platform. Reactive Strength: Drop Jump (DJ) test from a 30 cm box to calculate the Reactive Strength Index (RSI = jump height / contact time).
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
OTHER
Masking
NONE
Enrollment
30
An 8-week periodized resisted sprint training protocol using weighted sleds. Sessions are performed twice weekly over a 15-meter sprint distance, immediately following a standardized warm-up. Participants are assigned to sled towing loads equivalent to 10%, 15%, or 20% of their individual body weight (BW). Training volume progresses systematically from 2 sets of 3 repetitions (Weeks 1-2) to 3 sets of 4 repetitions (Weeks 7-8) with 2 minutes of inter-repetition rest and 3 minutes of inter-set rest.
Bitlis Eren University
Bitlis, Central, Turkey (Türkiye)
Linear Sprint Performance (5m, 10m, and 15m Sprint Times)
Linear sprint performance measured over 5 meters (acceleration), 10 meters, and 15 meters using a high-precision wireless photocell timing system. Times are measured in seconds (s), where lower values indicate better sprint performance.
Time frame: Baseline (Pre-test) and 8 weeks (Post-test)
Squat Jump (SJ) Height
Lower-limb concentric explosive power output measured via Squat Jump test on a digital contact mat/force platform. Surcharge from arm swing is isolated by keeping hands on hips. Jump height is measured in centimeters (cm), where higher values indicate greater explosive power output.
Time frame: Baseline (Pre-test) and 8 weeks (Post-test)
Countermovement Jump (CMJ) Height
Stretch-shortening cycle (SSC) performance and lower-limb reactive power measured via Countermovement Jump test on a digital contact mat/force platform. Jump height is recorded in centimeters (cm), where higher values represent superior vertical jump capacity.
Time frame: Baseline (Pre-test) and 8 weeks (Post-test)
Reactive Strength Index (RSI)
Reactive strength capacity and neuromuscular stiffness assessed via Drop Jump (DJ) test from a 30 cm box. Calculated as jump height (meters) divided by ground contact time (seconds) \[RSI = Jump Height (m) / Contact Time (s)\]. Higher index scores reflect better reactive strength and shorter contact time.
Time frame: Baseline (Pre-test) and 8 weeks (Post-test)
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