Effects of Resisted Versus Unresisted Sprint Training on Sprint Force-Velocity Profile in Youth Footballers

Effects of Resisted Versus Non-resisted Sprint Training on Countermovement Jump and Sprint Force-velocity Profile in Youth Footballers: a Randomised Controlled Trial

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.

Inclusion Criteria:

• Male football (soccer) player aged 13 to 17 years.
• Registered Under-14 or Juvenile player in an organized football program/club/league.
• At least 1 year of organized football experience.
• Current health-system affiliation (e.g., EPS).
• Provided informed assent; parent/guardian provided written informed consent (for minors).
• Able to attend and comply with the sessional training and testing protocol.

Exclusion Criteria:

• Current musculoskeletal complaint or injury at baseline.
• Ongoing rehabilitation at baseline.
• Logistical constraints preventing participation in the sessional protocol (e.g., inability to attend required sessions/assessments).
• Injury incurred during the intervention that prevents safe continuation (participant will be withdrawn).