Strength Testing After Anterior Cruciate Ligament Reconstruction: A Prospective Cohort Study Investigating Overlap of Tests

Barfod, KW, Feller, JA, Clark, R, Hartwig, T, Devitt, BM, and Webster, KE. Strength testing after anterior cruciate ligament reconstruction: A prospective cohort study investigating overlap of tests. J Strength Cond Res 33(11): 3145-3150, 2019-The purpose of the present study was to determine whether overlap (redundancy) exists between individual tests in a comprehensive strength testing protocol used after anterior cruciate ligament reconstruction (ACLR). If overlap is present, one or more components of the protocol could potentially be omitted to make the testing protocol more efficient, but without compromising the usefulness of the testing. Sixty-nine patients (46 male and 23 female patients; mean age 28 years) were strength tested at 6 and 12 months after ACLR as part of a prospective cohort study. The following knee flexor and extensor strength tests were performed: isokinetic concentric strength at 60 and 180°·s, isokinetic eccentric strength at 60°·s, and isometric knee flexor strength at 60° flexion. Peak and average torque values were extracted, and the ratio between the operated and non-operated limb was calculated as a limb symmetry index. Overlap of strength tests was investigated by fitting a linear regression model to the data with an R threshold of 0.56 used as an indication of overlap. Overlap between peak and mean torque was present for extensor and flexor concentric and eccentric measurements at 12 months and for concentric measurements at 6 months. Peak torque measurements were therefore used for subsequent analysis. Concentric extensor peak torque at 60 and 180°·s showed overlap at 6 months (R = 0.73) but not at 12 months (R = 0.37). No other overlap was identified. In conclusion, there is little room for omission of individual strength testing protocol components because of the lack of overlap between tests. Isometric, eccentric, and concentric tests may all provide unique information and all, therefore, should be considered for inclusion.