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Objective:To examine the effect of anterior cruciate ligament(ACL)reconstruction on spinal-reflex and corticospinal excitability of the quadri-ceps muscle.Methods:A comprehensive electronic database search was performed to identify studies that objectively measured Hoffmann reflex to muscle response ratio,motor threshold,and motor evoked potentials after ACL reconstruction.Pooled standardized mean differences(SMDs)were com-puted using a random effects meta-analysis model.Results:A total of 13 studies were eligible for analysis.The Hoffmann reflex to muscle response ratio was significantly higher on both the recon-structed and non-reconstructed legs when compared with the healthy control leg(SMD = 0.28,95％confidence interval(95％CI):0.08-0.49,p = 0.006 and SMD = 0.22,95％CI:0.04-0.40,p = 0.016,respectively)but did not differ between legs(SMD = 0.10,95％CI:-0.01 to 0.21,p = 0.078).The motor threshold was significantly higher on both the reconstructed(SMD = 0.76,95％CI:0.40-1.12,p ＜ 0.001)and non-recon-structed legs(SMD = 0.47,95％CI:0.00-0.95,p = 0.049)when compared with the legs of healthy controls.The reconstructed leg also had a higher motor threshold when compared with the non-reconstructed leg(SMD = 0.20,95％CI:0.06-0.34,p = 0.005).These changes were paral-leled by bilateral reductions in quadriceps strength(ACL reconstructed:SMD =-0.78,95％CI:-1.07 to-0.49,p ＜ 0.001;non-reconstructed:SMD =-0.32,95％CI:-0.63 to-0.01,p = 0.042)and quadriceps voluntary activation(ACL reconstructed:SMD =-0.73,95％CI:-0.97 to-0.50,p ＜ 0.001;non-reconstructed:SMD =-0.55,95％CI:-0.82 to-0.27,p ＜ 0.001)when compared with healthy controls.Conclusion:There is increased excitability of the spinal-reflex pathways and reduced excitability of the corticospinal pathways following ACL reconstruction.These changes are paralleled by reductions in quadriceps strength and voluntary activation,suggesting that rehabilitation inter-ventions should focus on normalizing the excitability of neural pathways to effectively address quadriceps dysfunction after ACL reconstruction.