Each year, thousands of athletes worldwide suffer from anterior cruciate ligament (ACL) injuries, with non-contact injuries being particularly prevalent. These often occur during deceleration movements - slowing down after a sprint, changing direction, or landing from a jump. While athletes excel at generating force during acceleration, absorbing forces during deceleration proves far more challenging.

The numbers are staggering: during maximum sprinting, peak forces range from 2.2 to 4.4 times body weight. However, during deceleration, impact forces surge to 5.9 times body weight - an increase of 1.3 to 2.7 times. These forces place immense strain on the knee joint and surrounding soft tissues, making proper mechanics and strength critical for both injury prevention and effective rehabilitation.

The Current Focus on Deceleration: Is It Enough?

Deceleration is undeniably a key injury mechanism. Coaches and practitioners have rightly begun incorporating braking patterns into ACL rehabilitation. Strengthening the body’s ability to absorb and control these forces is essential for reducing the risk of injury. However, focusing solely on deceleration patterns is insufficient.

This reductionist approach is comparable to teaching a boxer how to take a punch but not how to avoid one. It emphasises quantitative improvements - such as eccentric force production (RFD) and muscle strength - while overlooking qualitative aspects like movement skill and coordination.

The Missing Element: Braking Skill

While building strength is necessary, it must work in harmony with neuromuscular coordination and motor control. Successfully navigating the chaotic demands of sports requires athletes to brake skilfully, redistributing forces across multiple joints (hips, knees, ankles) rather than concentrating strain on the knee alone. Training should focus not only on "how strong" the athlete is but also on "how well" they move under dynamic and unpredictable conditions.

Therefore, a holistic approach is needed - one that trains strength and force production alongside coordination and motor control.

Key Patterns To Skilful Braking

Is there a good way and a bad way to brake? Probably not.
However, during effective deceleration, certain movement patterns consistently emerge across different sporting scenarios. These patterns are not limited to one specific braking situation; rather, they appear repeatedly in various contexts, highlighting their universality and efficiency.

Athletes adopt these movement patterns not only because they leverage the body's anatomy effectively - helping them achieve their goals - but also because they allow for adaptability in unpredictable environments. These movement solutions are shaped by the conditions or constraints - anything that influences how a person moves - of the task, the individual, and the environment, leading athletes to rely on them due to their stability, efficiency, and adaptability.

In braking these so-called 'attractors' or 'invariants' - the stable, economical, and efficient patterns of movement - include the following:

1. Foot Plant From Above

When the hip of the lead leg is extended prior to the foot contacting the ground, the muscles in the leg contract and create pretension before the foot contacts the ground and receives the ground reaction force. This subtle movement - which actually looks like the foot clawing back toward the ground prior to contact - creates pretension in the hamstrings, gluteus, and back muscles - essential to stiffening the leg before being exposed to the ground reaction force. This translates to an active landing, which, contrary to a passive landing (sliding-in of the foot), ensures the leg is tensioned and the ACL protected.  

2. Bending At The Hips

Bending at the hip is important during braking for three reasons. 
A) It is an effective pattern that emerges when external forces are high. Mover's adopt this pattern because the ground reaction forces are so high (up to 5.9 x bodyweight) that the body must quickly and effectively spread or share the forces over a larger area.  Diverging peak forces away from the knee and dissipating energy to the large muscles of the hip joint is effective.

B) Bending at the hip means the knee and hip joint angles are coupled. This means that the muscles that cross both joints - mainly the hamstrings and quadriceps - can work together in a co-contraction (when both muscles contract together) at their optimal force-producing length to actively control the joints during dynamic movement. This teamwork between the hip and knee, known as co-variation in the literature, ensures whatever happens at the knee is compensated for by the hip, and vice versa. 

C) Bending at the hip lengthens the hamstrings (just try bending over to touch your toes!) which pulls on its attachment distally - the fibula and more importantly the tibia. This helps the ACL preventing excessive anterior translation of the tibia relative to the femur. This offloads the stress on the ACL ligament during peak breaking forces, protecting it from injury. 

3. Back Leg Close

We often focus on what the front leg is doing during braking - however the position of the back leg is very important too. When the mover quickly pulls the back leg forward it creates internal rotation at the hip - lengthening and tightening the Iliotibial band and gluteus muscles. The resulting tension in the muscular and connective tissue on the lateral aspect of the thigh prevent the knee from sliding forward or rotating inward - two patterns often responsible for ACL rupture. A secondary benefit to this pattern is it quickly prepares the mover to take another step, by doing so they can divide external forces over multiple steps and avoid peak forces that would otherwise be too high to be managed within a 1-step stopping pattern. 

Penultimate Step Vs Ultimate Step

Properly managing the deceleration process by optimising the penultimate step can help in reducing the load experienced during the final step, thereby enhancing performance and reducing injury risk. This is of particular importance in open skills, where the braking is unexpected. Improving an athlete’s braking skill - by adopting a more stable and adaptable movement pattern - may facilitate a more effective penultimate step braking strategy that decreases the braking demand during the final step of reactive cutting.

Penultimate Step - Unstable vs Stable 

Ultimate Step - Unstable Vs Stable

How can we encourage these movement patterns during ACL rehabilitation and prevention while still addressing the necessary strength development?

This leads us to the next stage: a framework that seamlessly integrates both strength and skill acquisition in a progressive manner, ensuring a more complete approach to ACL injury prevention and rehabilitation.

The New Framework: Integrating Strength and Coordination

Michael de Levie’s approach advocates for a more integrated framework for ACL rehabilitation, combining quantitative strength training with qualitative skill development. This method emphasises progressive exposure to braking patterns, incorporating motor control, perturbations, and movement variability at each stage of recovery.

Phase	Focus	Goals	Example Exercises
Early Phase	- Build core and posterior chain stability. - Minimise stress on the knee.	- Lay the foundation for proper movement. - Protect the joint while building strength.	- Static hinge movements (e.g., Romanian deadlifts with light loads). - Core stability with elastic bands.
Intermediate Phase	- Introduce dynamic movement patterns. - Add perturbations for increased challenge.	- Train co-contractions around the knee. - Develop neuromuscular control under variable loads.	- Walking lunges with aqua bags. - Triple flexion with elastic bands. - Start-stops over 1–2 meters (low speed).
Advanced Phase	- Incorporate high-speed movements. - Progress to sport-specific patterns.	- Build braking efficiency. - Develop coordination in high-speed and multi-directional movements.	- Sprint deceleration drills. - Zigzag cutting patterns. - Start-stops over 5–10 meters (average-high speed).
Final Phase	- Simulate chaotic conditions. - Add cognitive dual-task challenges.	- Prepare for real-game scenarios. - Improve adaptability and decision-making under pressure.	- Multi-directional start-stops with random cues. - Agility drills with memory tasks or reaction components.

Key Principles:

1. Build a Robust Muscular System:
   - Strengthen the core and posterior chain to stabilize the pelvis and redirect forces away from the knee.
   - Train eccentric strength to absorb high forces effectively.

2. Develop Braking Patterns:
   - Encourage energy redistribution across multiple joints to lower peak forces at the knee.
   - Focus on motor control and coordination, ensuring proper timing and joint coupling.

3. Use Perturbation Training:
   - Introduce unpredictable, unstable loads (e.g., water weights, dangling weights) to simulate real-world demands.
   - Train co-contractions around the knee to improve joint stability and control under chaotic conditions.

Understanding Progressions in the Rehabilitation Framework

Early Phase: Building Foundations
- What it involves: Target the torso and core, especially the extensor muscles, to lay a foundation for stability.
- Why: During this phase, the knee cannot handle high loads, but the core and posterior chain can be safely trained. This prepares the athlete for more advanced movements while protecting the joint.
- Examples:
  - Static hinge movements (e.g., Romanian deadlifts with light loads).
  - Core stability exercises with elastic bands to resist external disruption.

Intermediate Phase: Introducing Perturbations
- What it involves: Gradually introduce movement patterns with increasing complexity and load. Use tools like aqua bags to create dynamic, unpredictable forces.
- Why: Perturbation training challenges the athlete to stabilise their knee under shifting conditions, simulating the demands of sports.
- Examples:
  - Triple flexion patterns (hip, knee, ankle) with elastic bands.
  - Dynamic lunges with aqua bags to train co-contractions around the knee.

Advanced Phase: Functional, High-Speed Movements
- What it involves: Progress to sport-specific movements at higher speeds and with added time pressure. Include cutting, zigzag patterns, and multi-directional movements.
- Why: This phase prepares the athlete for the chaotic nature of competition, ensuring they can brake efficiently and avoid injury.
- Examples:
  - Start-stop drills (e.g., sprints with abrupt halts).
  - Zigzag cutting patterns with time constraints.

Final Phase: Chaotic, Dual-Task Environments
- What it involves: Introduce unpredictability and cognitive challenges. Combine physical movements with tasks like memorizing sequences or mirroring a partner’s movements.
- Why: This phase replicates the chaotic, multi-tasking environment of sports, training the athlete to perform under pressure.
- Examples:
  - Start-stop movements with random directional cues.
  - Agility drills incorporating reaction-based tasks.

Practical Example Progressions 

1. Static Movements (Early Phase):
   - Forward and sideways lunges with elastic bands.
   - Static split stance holds with tank punches.

2. Dynamic Movements (Intermediate Phase):
   - Walking lunges with perturbations from aqua bags.
   - Start-stop drills over short distances (1-2 meters) at low speeds.

3. High-Speed Movements (Advanced Phase):
   - Sprint deceleration drills with sharp directional changes.
   - Zigzag cutting patterns with increasing complexity.

4. Chaotic Movements (Final Phase):
   - Multi-directional start-stops (forward, backward, sideways).
   - Dual-task drills incorporating memory or reaction components.

Conclusion: Treating the Root Cause of ACL Injuries

A holistic rehabilitation approach that integrates strength, coordination, and skill is key to reducing ACL re-injury rates. By training athletes to brake skilfully and adapt to chaotic conditions, practitioners can address the root causes of injury - not just the symptoms. Michael de Levie’s framework provides a practical, evidence-based path for physiotherapists, athletic trainers, and strength coaches to guide athletes toward safer, more efficient movement patterns. 

Acknowledgment

Special thanks to Michael de Levie, a leading sports physiotherapist and knee specialist at FysioHolland, for contributing his expertise to this article. As the founder of The Knee Club and chairman of the knee knowledge circle, Michael’s innovative approach to ACL rehabilitation continues to shape the future of injury prevention and recovery.