This randomised, controlled, two-arm trial evaluates whether light resisted sprint training (sled towing at 20% of body mass) produces superior improvements in 30 m sprint mechanical outputs compared with matched-dose unresisted sprint training in youth footballers. Participants complete two supervised sessions per week for six consecutive weeks, integrated into normal academy microcycles on the same artificial-turf surface. Primary outcomes are changes in sprint-derived force-velocity-power profile parameters and 30 m sprint performance, with secondary outcomes including countermovement jump height and anthropometrics.
The study uses a parallel-group randomised design. Allocation is stratified by squad category (Under-14 and Juvenile) with simple randomisation within strata using computer-generated random numbers prepared by a researcher not involved in training delivery. The intervention is delivered on a third-generation artificial-turf pitch at a youth academy integrated within a professional development pathway. Forty-four outfield players from two squads are enrolled. Both arms complete 20 m maximal sprints with identical volume and rest structure (3 sets × 5 repetitions, 45 s inter-repetition rest, 3 min inter-set rest). The experimental arm performs sled towing at 20% body mass (sled tare 3 kg plus plates), whereas the comparator arm performs unresisted maximal sprints. No additional lower-limb strength or speed work beyond the head coach's standard plan is introduced during the intervention period. Primary outcomes are derived from 30 m sprint profiling, using high-speed video and the MySprint application to compute split times and estimate sprint mechanical variables within the Morin-Samozino framework. Outcome assessors/video analysts and the statistician are blinded to group codes, while full participant blinding is not feasible due to the presence of the sled.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
TREATMENT
Masking
SINGLE
Enrollment
44
20 m maximal sprints towing a sled loaded to 20% of individual body mass (sled tare 3 kg; plates added). 3 sets × 5 repetitions, 45 s inter-rep rest, 3 min inter-set rest; two supervised sessions/week for six weeks, conducted at the start of squad training, on the same artificial-turf surface.
20 m maximal sprints without external resistance; dose and rest schedule identical to RST (3 × 5 × 20 m; 45 s; 3 min); two sessions/week for six weeks; same surface and session placement; standard team training continues.
Universidad de Antioquia
Medellín, Antioquia, Colombia
Change from baseline to post-intervention in best 30 m sprint time
Best (fastest) 30 m sprint time, expressed in seconds (s). The reported value is the best 30 m time (s).
Time frame: From baseline assessment (within 1 week prior to first training session) to post-intervention assessment (within 1 week after the final training session), over the 6-week intervention period.
Change from baseline to post-intervention in theoretical maximal horizontal force (F0)
Sprint-derived theoretical maximal horizontal force (F0), expressed relative to body mass (N/kg).
Time frame: From baseline assessment (within 1 week prior to first training session) to post-intervention assessment (within 1 week after the final training session), over the 6-week intervention period.
Change from baseline to post-intervention in peak sprint velocity
Peak velocity reached during the sprint assessment, expressed in meters per second (m/s).
Time frame: From baseline assessment (within 1 week prior to first training session) to post-intervention assessment (within 1 week after the final training session), over the 6-week intervention period.
Change from baseline to post-intervention in rate of decrease in RF with velocity (DRF)
Sprint-derived rate of decrease in RF with velocity (DRF), expressed as % per m.
Time frame: From baseline assessment (within 1 week prior to first training session) to post-intervention assessment (within 1 week after the final training session), over the 6-week intervention period.
Change from baseline to post-intervention in peak ratio of horizontal force (RF_peak)
Sprint-derived peak ratio of horizontal force (RF\_peak), expressed as percentage (%).
Time frame: From baseline assessment (within 1 week prior to first training session) to post-intervention assessment (within 1 week after the final training session), over the 6-week intervention period.
Change from baseline to post-intervention in ratio of horizontal force (RF)
Sprint-derived ratio of horizontal force (RF), expressed as percentage (%).
Time frame: From baseline assessment (within 1 week prior to first training session) to post-intervention assessment (within 1 week after the final training session), over the 6-week intervention period.
Change from baseline to post-intervention in maximal horizontal power (Pmax)
Sprint-derived maximal horizontal power (Pmax), expressed relative to body mass (W/kg).
Time frame: From baseline assessment (within 1 week prior to first training session) to post-intervention assessment (within 1 week after the final training session), over the 6-week intervention period.
Change from baseline to post-intervention in theoretical maximal running velocity (V0)
Sprint-derived theoretical maximal running velocity (V0), expressed in meters per second (m/s).
Time frame: From baseline assessment (within 1 week prior to first training session) to post-intervention assessment (within 1 week after the final training session), over the 6-week intervention period.
Change from baseline to post-intervention in countermovement jump (CMJ) height
Countermovement jump (CMJ) height, expressed in centimeters (cm). The reported value is CMJ height (cm).
Time frame: From baseline assessment (within 1 week prior to first training session) to post-intervention assessment (within 1 week after the final training session), over the 6-week intervention period.
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