Performance across the isokinetic velocity spectrum: Interpretation for individuals after anterior cruciate ligament reconstruction

Background: Quadriceps strength recovery is a focal point of rehabilitation after anterior cruciate ligament reconstruction. Quadriceps function at slow, moderate and faster isokinetic speeds may prove useful to identify individuals with abnormal muscular force-velocity properties. This study's purpose was to investigate changes in quadriceps peak torque and total work across the isokinetic velocity spectrum and assess between the reconstructed limb, uninvolved limb and a control group limb. Methods: 20 participants after primary anterior cruciate ligament reconstruction and 20 control participants performed 5 repetitions of maximal effort knee extension and flexion at 20°/s, 60°/s, 120°/s, 240°/s, 400°/s. Data were averaged across the middle 3 repetitions at each isokinetic velocity and two-way repeated measures analysis of variance models were conducted to evaluate differences among the limbs. Post-hoc polynomial trend analyses and limb differences at each velocity were evaluated using Bonferroni adjusted contrasts. Findings: The involved limb demonstrated lower peak torque and total work at all isokinetic velocities compared to the uninvolved and control limbs. There were no differences between the uninvolved limb and control group limb at any velocity. Trend analyses revealed the involved limb decreased at a significantly different rate across the isokinetic velocity spectrum, compared to the uninvolved and control limbs, for peak torque and total work. Interpretation: Individuals 4 months after anterior cruciate ligament reconstruction demonstrate maximal and sustained quadriceps strength deficits compared to their uninvolved limb and control individuals. The convergence of peak torque and total work across the isokinetic velocity spectrum indicates that slower isokinetic velocities are more discriminative than faster isokinetic velocities for quadriceps testing.