Contractile rate of force development after anterior cruciate ligament reconstruction: a comprehensive review and meta-analysis

Key points

1. 01Rate of force development (RFD) is how fast a muscle builds force at the start of a contraction, which matters for fast actions like landing, cutting, and catching a stumble, separate from raw maximal strength.
2. 02Comparing the reconstructed leg to the uninjured leg, knee extensor RFD deficits were large early-phase (SMD -1.07) and late-phase (SMD -0.85), with knee flexor deficits moderate (SMD -0.74 and -0.79).
3. 03Compared with healthy controls the deficits were larger still, with knee extensor SMD -1.42 (early) and -1.09 (late).
4. 04Between-limb RFD asymmetry was highest in the first months (up to 57% for the knee extensors) and could still be present 2 to 4 years after surgery.
5. 05RFD is trainable, so the authors recommend explosive and high-intent resistance training to rebuild rapid force before return to sport.

How it was conducted

Design

Systematic review and meta-analysis of 10 non-randomized observational studies (no RCTs available), following PRISMA

Search

Web of Science, SPORTDiscus, PubMed-MEDLINE, ScienceDirect to August 2019; quality rated with Newcastle-Ottawa Scale (all moderate to high)

Participants

246 individuals post-ACLR (109 female, 137 male), mean age 18 to 29.6 years, 4 to 49 months post-surgery; 4 studies also had healthy controls

Outcomes

Isometric knee extensor and flexor RFD, early-phase (<100 ms) and late-phase (>=100 ms), as between-limb asymmetry and vs healthy controls

Analysis

Random-effects meta-analysis pooling standardized mean differences (SMD), inverse-variance weighted; heterogeneity by I2 and tau-square

What they found

• Reconstructed vs uninjured limb, knee extensor RFD: early-phase SMD -1.07 (95% CI -1.46 to -0.68; I2 = 22%), late-phase SMD -0.85 (95% CI -1.27 to -0.42; I2 = 79%).
• Reconstructed vs uninjured limb, knee flexor RFD: early-phase SMD -0.74 (95% CI -1.19 to -0.29), late-phase SMD -0.79 (95% CI -1.19 to -0.39).
• ACLR vs healthy controls, knee extensor RFD: early-phase SMD -1.42 (95% CI -2.10 to -0.73), late-phase SMD -1.09 (95% CI -1.81 to -0.38).
• ACLR vs healthy controls, knee flexor RFD: early-phase SMD -0.78 (95% CI -1.96 to -0.39), late-phase SMD -1.14 (95% CI -1.60 to -0.67).
• Between-limb knee extensor RFD asymmetry ranged 7% to 57% and knee flexor 5% to 32% across time intervals; asymmetry could persist 2 to 4 years after surgery.

Limitations

• All included studies were observational with no randomized trials, and quality varied with predominantly volunteer samples.
• Only 246 participants total, mostly young males, limiting generalizability, and the small study count prevented subgroup analysis or meta-regression.
• Rehabilitation protocols and graft types varied and were poorly described, and there were no pre-injury RFD data, so confounders may have distorted the ACLR-RFD relationship.
• Moderate to high statistical heterogeneity was present for several pooled comparisons.

Why it matters

For patients

After an ACL reconstruction your operated leg may stay slower at producing force for a long time, even when ordinary strength looks recovered, so rebuilding explosive power matters.

For clinicians

Consider adding RFD testing alongside peak-strength and limb-symmetry assessments during ACLR rehab, and program explosive or ballistic resistance training before return to sport.

For readers

Rate of force development reveals rapid-force deficits after ACL reconstruction that maximal strength testing alone can miss.