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.
Male football players aged chronologically between 13 and 14 years.
Minimum of 2 years of active, licensed competitive football experience in a club or academy.
Regular attendance at scheduled team training sessions.
Written Informed Consent/Assent signed by both the participant (Child Assent Form) and parent/legal guardian (Parental Consent Form).
Chronological age <13 or >14 years.
Presence of chronic, cardiovascular, metabolic, or respiratory conditions (e.g., asthma) that pose risks during high-intensity maximal exercise.
Regular use of performance-enhancing supplements or medications affecting physiological and neuromuscular responses.
Absence from more than 10% of prescribed sled training sessions (2 or more sessions out of 16).
Parallel
Resisted Sled Sprint Training
Other interventionAn 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.
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.
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.
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.
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.
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