We have studied neuromuscular changes and adaptation of the knee extensors in thirty one patients (25 males, 6 females), 30 ± 8 years, body mass 76 ± 9 kg, height 1.75 ± 0.10 m (mean ± SD) following anterior cruciate ligament reconstruction (ACLR). A major rehabilitative goal is to restore optimum functional performance. We reported (Drechsler et al. 2005), that at 3 months post surgery, the knees were stable and most patients (n = 27) were pain free with minimal swelling; they had achieved full activation but still had muscle weakness. At both 1 and 3 months post surgery, the surface electromyographic (EMG) median frequency and amplitude were significantly lower (P<0.05) in the injured compared to the uninjured limb. Further work has shown that there were no significant differences in these parameters between the uninvolved limbs and those of 20 age-matched and recreationally active control subjects. Detailed analysis of individual EMG power spectrum plots at maximum voluntary isometric contraction (MVIC) and linear regression analysis were then used to investigate whether any independent variables tested 1 month after ACLR could predict 1 year functional status using the Hughston Clinic Knee Questionnaire (Hooper et al. 2002) completed 1, 3 and 12 months after surgery. Muscle function tests included quadriceps femoris MVIC twitch superimposition and Fast Fourier Transformation of surface EMG recordings (5000 cycles per s, filter 10-250 Hz) of rectus femoris to determine median frequency and amplitude at MVIC. In addition to the reduced median frequencies observed, paired t tests showed that the magnitude (mv²) of the EMG power density spectrum during MVIC was consistently and significantly lowered (P<0.001) in the injured compared to the uninjured limb, 1 month after surgery. Step-wise forward linear regression analysis showed that the functional questionnaire_{(step 1)} combined with activation or strength level_{(step 2)} assessed 1 month after ACLR were the most effective estimates of functional status 1 year after surgery (R=0.80, adjusted R²=0.59, F₍₂₎=13.9, P<0.0001). Our results showed restoration of volitional quadriceps activation, lowered motor unit firing rates and a significant reduction in the magnitude of the frequency spectra after ACLR. Regression analysis showed that functional status combined with activation/strength assessment at 1 month can predict knee function 1 year after surgery. These findings suggest changes in patterns of activation and in the recruitment patterns of Type 11b fast contracting muscle fibres (Pette & Vrbová, 1999). In addition, analysis of the individual power spectrum plots may help to identify an inability to increase motor unit firing capability which could be addressed by selective intervention.