The purpose of this study was to determine if there were any reliable predictors for achieving jogging requirements after anterior cruciate ligament (ACL) reconstruction. We analyzed associations among variables collected from 128 subjects at 12 weeks postoperatively, including jogging parameters (i.e. pain, apprehension, speed, and distance), the isokinetic muscle strength of the leg extensors, the knee stability, and patient's profiles (i.e. age, sex, activity level, body mass index (BMI), meniscectomy, and cartilage injury).Jogging parameters were significantly correlated with the isokinetic muscle strength of leg extensors, but not with the knee stability. With the jogging ability of achieving a distance of 2000m at a velicity of 9km/h being an objective variable, a logistic regression analysis revealed that the isokinetic muscle strength of leg extensors and BMI were considered relevant. Using a receiver operating characteristic (ROC) curve analysis and a contingency table, the cut-off values of the isokinetic muscle strength of leg extensors to the uninvolved side and body weight were 85% and 1.9Nm/kg, respectively, whose sensitivity and specificity were 0.90 and 0.82, respectively. Therefore, we concluded that the isokinetic muscle strength of leg extensors is a reliable predictor for projecting the timing to start jogging after ACL reconstruction.

The six major determinants of gait, as proposed by Saunders et al., were reviewed. The results showed that each of the first three determinants (pelvic rotation, pelvic list, and stance phase knee flexion) have only a minor effect on decreasing the vertical displacement of the center of gravity (COG). The major determinant of COG displacement is heel rise, and the second is the inclination of the lower extremity in the stance phase. In spite of the assumption that decreasing the COG displacement decreases gait energy consumption, the energy required for walking with a flat COG trajectory increased dramatically. Therefore, the major gait determinants as defined by Saunders et al. should be corrected in terms of both the COG displacement and energetics.