Associations between isometric quadriceps strength characteristics, knee flexion angles, and knee extension moments during single leg step down and landing tasks after anterior cruciate ligament reconstruction.

BACKGROUND

It is unclear of how peak knee extension torque and early rate of torque development outcomes are related to lower extremity loading and sagittal plane movement in activities of daily living and landing tasks despite consistent deficits after anterior cruciate ligament reconstruction. The purpose of this cross-section study is to assess the ability of quadriceps strength characteristics to predict movement patterns during a step down and single leg drop crossover hopping tasks.

METHODS

Fifty-two individuals with a unilateral history of anterior cruciate ligament reconstruction completed three trials of the step down and crossover hopping tasks on their involved limb. Participants completed three isometric knee extension contractions at 90° knee flexion with visual feedback to assess peak knee extension torque and rate of torque development during the first 0-100 ms and 100-200 ms of the contraction.

FINDINGS: Peak knee extension torque explained the greatest variance in peak knee extension moment (R2 = 40.4%, p < 0.001) and knee flexion angle (R2 = 46.7%, p < 0.001) during the crossover hop landing. Rate of torque development (0-100 ms) was the only predictor of knee flexion angle (R2 = 19.8%, p = 0.01) at initial contact during the crossover hopping landing. Rate of torque development (100-200 ms) explained 17.6% of the variance in peak knee extension moment during the step down (p = .03).

INTERPRETATION: Peak knee extension torque and early rate of torque development outcomes demonstrate limited relationships between movement of activities of daily living and sport-specific tasks. These limitations should be considered when interpreting the results of isometric strength testing in a clinical setting.