A Powerful ACL Injury Prevention Drill

One of my favorite drills for reducing non-contact ACL injury risk is a modified single-leg Star Excursion balance exercise performed on a narrow, four-inch-high platform. It looks deceptively simple. It is not.

Most ACL injuries don’t come from contact. They come from the athlete’s own body failing to control knee alignment, balance, and force during cutting, landing, or deceleration. Roughly seventy percent of all ACL tears are non-contact — and the predictors are well-documented.

Why This Drill, and Who It’s For

This drill is for change-of-direction athletes, runners, and active adults — anyone whose knee gets loaded on one leg under cutting, landing, or deceleration.

And more importantly, women carry an ACL injury risk that runs roughly six times higher than men. The Q-angle between the hip and knee is wider, hormonal cycles shift ligament laxity, and the quad-to-hamstring strength ratio often favors the quads — which pulls the tibia forward and stresses the ACL on landing. Layer in any imbalance at the hip, and the knee pays the bill.

The Star Excursion Balance Test was originally a clinical assessment — a way for physical therapists to measure dynamic postural control and predict who was at risk for lower-extremity injury. I’ve converted it into a training drill. Same pattern. Add an elevated, narrow surface. Now you’re training the system, not just measuring it.

This drill challenges five things at once:

• Hip stability — the muscle group that keeps your pelvis level when you stand on one leg.
• Glute activation — particularly the medius, which holds the knee from collapsing inward.
• Proprioception — the body’s sense of where it is in space.
• Balance — static and dynamic, on an unstable surface.
• Single-leg knee control — the ability to keep the knee tracking over the toes, not caving inward.

How the Drill Works

Stand single-leg on the narrow, elevated block. The platform forces ankle stability before anything else — if the ankle collapses, the knee follows, and the drill is over. From a controlled single-leg stance, reach the free leg in five directions:

• Front — toe taps forward.
• Side — lateral reach.
• 45-degree angle — diagonal forward-to-side.
• Straight back — posterior reach.
• Around — the full sweep behind the body.

The non-negotiable: the standing knee cannot collapse inward. If it does, the rep is wasted. Reach only as far as you can without losing knee alignment, foot stability, or pelvic level. The elevated surface is doing the work — raising neuromuscular demand and teaching the body to control movement under conditions similar to what happens in sport.

Injury prevention is not just about building stronger muscles — it’s about teaching the body how to control force, alignment, balance, and movement under pressure. Mackie Shilstone

The Research Behind It

The principles in this drill are backed by a long literature on dynamic postural control, single-leg neuromuscular training, hip stabilization, and the biomechanical predictors of non-contact ACL injury. Star Excursion reach asymmetry has been predicted to lower-extremity injury in high school athletes. Knee valgus angle at landing has been shown to predict ACL injury risk in female athletes. Hip-stabilizer training has been shown to reduce that valgus pattern. The drill consolidates all of these inputs into a single five-direction exercise.

The Safety Caveats

Because the surface is narrow and elevated, there’s a real risk of slipping, twisting the ankle, or overloading the joint if technique breaks down. A few rules:

• Start supervised. A coach or therapist watching the first sessions catches the faults you can’t feel.
• Build it on the floor first. Master the five-direction reach on flat ground before you elevate. If the floor version isn’t clean, the block version is dangerous.
• Slow it down. This is a control drill, not a tempo drill. Volume comes later.
• If the block feels too aggressive, drop it. Floor-level Star Excursion is still a powerful exercise.
• Progress gradually. Reach distance, time under tension, and difficulty all advance — but only after the previous level is automatic.

The Bottom Line

This is not simply a balance drill. It is movement re-education — designed to improve force control, joint stability, and athletic resilience. Train it consistently and the body learns to refuse the position that tears ACLs.

Stronger muscles matter. But the athletes who don’t tear ACLs are the ones whose bodies know how to control force, alignment, and balance under pressure. That’s what this drill teaches.

Be well. — Mackie

Mackie Shilstone

Integrative Performance Management · 43+ Years

America’s premier sports performance management and career-extension specialist. More than 3,000 professional athletes and teams over 43 years, including 14 years coaching Serena Williams, Peyton Manning, Michael Spinks, Bernard Hopkins, and Ozzie Smith. Former director of multiple hospital-based performance programs in New Orleans and 21-year official lifestyle management program director for MLB Umpire Medical Services. Currently serves on the Tulane University Kinesiology Advisory Board and volunteers in support of U.S. Army Special Operations Command. Author of seven books on health and performance. Mackie’s Maximum Wellness is his column at MaxWell Nutrition.