Author: Eline M Nijmeijer et al
Journal: Journal of Sport Sciences (2026)

Anterior cruciate ligament (ACL) injuries remain a major concern in female football, particularly among youth players who show the highest injury rates in sport. Traditional prevention programs have improved awareness but demonstrate inconsistent biomechanical outcomes.

Recent research in motor learning and biomechanics suggests that implicit learning strategies — which focus attention externally and avoid overloading the athlete with technical details — may better improve movement quality and robustness.

The authors investigated whether combining skilled model video instruction with individualized self‑video feedback and implicit verbal feedback would produce measurable and sustainable improvements in lower‑limb biomechanics relevant to ACL injury prevention.

Objective

Participants and Methods

• Participants: 48 talented female soccer players (age ≈ 15 years) from a Dutch professional club’s youth academy.
• Design: Controlled, 4‑group study with repeated measures — pre‑test, post‑test, and retention (1 week later):
  1. CTRL: General task instruction only.
  2. VIDEO: Skilled model demonstration.
  3. VIDEO + SELF: Skilled model + video feedback of own execution.
  4. VIDEO + SELF + VB: Skilled model + own video + individualized implicit verbal feedback.
• Tasks: Unanticipated sidestep cutting, single‑leg, and double‑leg landing tasks — ten repetitions per session over four weeks.
• Feedback Design:
  • All video shown from frontal and sagittal views at 70% speed.
  • Implicit verbal cues focused on external analogies (e.g., “imagine your knee is a headlight pointing forward”) rather than internal, joint‑specific commands.
  • Feedback was individualized based on biomechanical data such as frontal knee moment, supporting a gamified “performance score” for each athlete.
• Measurements: 3D motion analysis and force plate data quantified hip and knee kinematics and kinetics during sidestep cutting — a movement strongly associated with ACL injury risk.

Key Findings

Overall Intervention Effects

Across all groups, movement patterns improved from baseline to one‑week retention, indicating general learning from four weeks of focused movement practice. However, the VIDEO + SELF + VB group demonstrated the most substantial and retained improvements.

Biomechanical Improvements

At retention:

• Hip Flexion: +2–3° increase
• Knee Flexion: +2.5° increase
• Hip Abduction Angle: −5° reduction
• Knee Adduction Angle: −10° reduction
• Hip Abduction Moment: −0.96 Nm/kg reduction

These changes—more flexion in the sagittal plane and less movement in the frontal plane—represent safer, more stable cutting mechanics known to lower ACL loading risk.

Group Comparisons

• VIDEO + SELF + VB group: Significant improvements across four major kinematic variables (hip/knee flexion and adduction/abduction).
• VIDEO + SELF group: Improvements present but smaller and less retained.
• VIDEO only or control: Minimal long-term effect beyond short-term adjustments.

Seventy percent of participants receiving both verbal and video feedback preferred this combined format, suggesting higher engagement and usability.

Interpretation

The integration of individualized implicit verbal feedback enhanced the effectiveness of video-based motor learning tools, helping players internalize improved movement patterns beyond explicit instruction.

The improvements demonstrate that combining multiple feedback modalities leads to synergistic learning effects — video guides perception, self-video supports self‑correction, and implicit verbal cues channel attention to effective movement qualities.

This individualized approach appears particularly important for adolescent female players, who may benefit from meaningful cues and autonomy-supportive learning environments to foster lasting biomechanical change.

Practical Implications

• Coaches and rehabilitation specialists should blend video modeling, self-observation, and simple, analogy-based cues to refine movement technique.
• Digital tools such as tablet-based delayed playback or motion-analysis apps could make this approach feasible in everyday training.
• Personalized cues (“push off like a rocket,” “keep your headlights forward”) are more effective than one-size-fits-all instructions.
• This methodology supports both injury prevention and motor learning efficiency, moving beyond prescriptive coaching toward adaptive athlete-centered training.

Limitations

• Only short-term retention (1 week) was assessed; long-term motor retention remains unknown.
• The study was conducted in a laboratory rather than in match or field settings.
• Feedback dominance (frontal vs sagittal cues) was unbalanced.
• No verbal-only condition was included, limiting the ability to isolate verbal effects.

Key takeaway

Combining individualized video feedback with implicit verbal feedback results in the greatest and most sustainable improvements in movement execution among talented female soccer players.

This multimodal, learner-centered method optimizes motor learning, corrects risky cutting mechanics, and holds strong promise as an ACL injury prevention tool. Future research should assess long-term retention, real-field transfer, and application at elite and professional levels.

Context Within Recent Research

This study extends a growing body of evidence shifting ACL injury prevention paradigms from standardized drills to self-regulated, context-rich motor learning approaches:

• Benjaminse & Verhagen (2021) and Grooms et al. (2024) argue that neuromechanical injury prevention must include perception–action coupling and athlete autonomy.
• Bill et al. (2024) and Dos’Santos et al. (2019–2022) emphasize individualized technique feedback as the next frontier in risk mitigation.
• The present work by Nijmeijer et al. (2026) substantiates these theories with quantifiable biomechanical evidence in a youth female football context—bridging motor learning science and applied biomechanics.

It represents a decisive step toward evidence-based, individualized, and cognitively smart ACL injury prevention.

Note: This summary was generated with the assistance of Claude Opus 4.1 based on the original paper, with the aim of translating the research into practical insights for coaches and practitioners.