What are the best exercises for anterior cruciate ligament (ACL) rehabilitation?

Best Exercises for ACL Rehabilitation

Exercise should be the mainstay of ACL rehabilitation, with both closed kinetic chain (CKC) and open kinetic chain (OKC) exercises used throughout recovery, prioritizing CKC exercises in the first month to reduce patellofemoral pain risk. 1, 2

Early Phase (0-4 Weeks): Foundation Building

Start immediately with:

• Isometric quadriceps exercises (static quad sets, straight leg raises) - these can be safely prescribed during the first 2 postoperative weeks and accelerate knee range of motion recovery at 1 month without compromising stability 1
• Early weight-bearing as tolerated - improves early knee flexion/extension range without compromising knee laxity, and reduces patellofemoral pain from 35% to 8% in bone-patellar tendon grafts 1
• Closed kinetic chain exercises (leg press starting at 3 weeks, mini-squats, wall sits) - these should be prioritized over OKC exercises in the early phase to mitigate patellofemoral pain risk 2

Avoid: Full range OKC exercises before 4 weeks, especially with hamstring grafts which are more vulnerable to early OKC introduction 1

Intermediate Phase (4-12 Weeks): Strength Development

Add open kinetic chain exercises at 4 weeks:

• OKC knee extension (90-45° only) can be safely introduced as early as 4 weeks 2
• Both OKC and CKC exercises should be used for optimal quadriceps strength gains - evidence shows no significant difference in anterior tibial laxity between the two, but OKC may induce more anterior knee pain 1

Initiate at 3 weeks:

• Isokinetic hamstring strengthening using functional patterns (0-45° half squat pattern) improves quadriceps/hamstring strength and functional activities 1
• Eccentric cycle ergometer training starting at 3 weeks (versus 12 weeks) results in greater strength gains, better daily activity levels, and greater quadriceps hypertrophy persisting 1 year post-surgery, without affecting laxity, pain, or swelling 1

Key technical considerations:

• During squats: avoid excessive forward knee movement beyond toes and heels off ground (increases ACL loading); forward trunk tilt decreases ACL loading via increased hamstring activity 3
• During seated knee extension: position resistance pad more proximal on the lower leg (away from ankle) to decrease ACL force 3
• Knee flexion with quadriceps cocontraction near full extension (with 10% 1RM resistance) yields 32-50% quadriceps activation while maintaining posterior tibial pull (ACL-protective) 4

Advanced Phase (12+ Weeks): Return to Function

Implement progressive loading:

• Combined eccentric and plyometric training is more effective than either alone for improving balance, functional activities, subjective knee function, and psychological readiness 1
• Plyometric and agility training added to usual care improves subjective function and functional activities without increasing laxity or pain 1
• 8 weeks of plyometric exercise (regardless of intensity) has positive effects on knee function, impairments, and psychosocial status 1

Adjunctive interventions with evidence:

• Core stability exercises improve gait, subjective knee function, and range of motion 1, 5
• Blood flow restriction training excels in quadriceps strength enhancement 6, 7
• Whole-body vibration training shows superior results for quadriceps strength and limb symmetry index 6
• Functional resistance training and water-based training show best improvements in Lysholm scores 6

Critical Timing Considerations

Do not rush return to running before 12 weeks - most evidence suggests a minimum 12-week timeframe, though some protocols suggest 8-16 weeks. Prospective studies investigating safety of earlier return are lacking 1

Rehabilitation duration should be ≥9 months for optimal recovery guided by functional progress 7

Common Pitfalls to Avoid

• Hamstring grafts are more vulnerable to early OKC exercises compared to bone-patellar tendon-bone grafts - delay or modify accordingly 1
• Cross-education training shows conflicting evidence for quadriceps strength and no effect on hamstring strength, hop distance, balance, or proprioception - don't overemphasize contralateral limb training 1
• Whole-body vibration training shows inconsistent benefits despite some positive findings 7
• Avoid postoperative functional bracing - routine use is not recommended 2

Exercise Progression Framework

Progress based on criteria, not just time:

• Minimal pain/swelling
• Restored knee range of motion
• Adequate strength and limb symmetry (target ≥90% LSI for strength/hop tests; ≥100% for pivoting/contact sports) 2
• Tolerance to running loads

The control-chaos continuum should guide progression from controlled, predictable movements to unpredictable, sport-specific scenarios 8