Loading Behaviors Do Not Match Loading Abilities Postanterior Cruciate Ligament Reconstruction

Area of Science:

• Biomechanics
• Rehabilitation Science
• Motor Control

Background:

• Individuals post-anterior cruciate ligament reconstruction (ACLr) often display altered movement strategies, including underloading the surgical limb during submaximal tasks.
• The underlying reasons for this limb underloading in early rehabilitation remain unclear, with possibilities including task demand limitations or learned behaviors.

Purpose of the Study:

• To investigate whether limb underloading post-ACLr is due to an inability to meet task demands or is a learned behavior.
• To examine the influence of attention and feedback on limb loading symmetry in individuals after ACLr.

Main Methods:

• Twenty individuals post-ACLr and 20 healthy controls performed standing, sit-to-stand, and squat tasks under natural, instructed, and feedback conditions.
• Limb-loading symmetry was quantified using the between-limb ratio of vertical ground reaction force impulse.
• A 2 (group) × 3 (condition) repeated-measures General Linear Model analyzed the effects on limb-loading symmetry.

Main Results:

• Significant group-by-condition interactions were found for all tasks (P < 0.001).
• ACLr individuals showed greater asymmetry than controls in natural and instructed conditions but not feedback conditions.
• ACLr participants exhibited greater asymmetry compared to controls across natural and instructed conditions, indicating a persistent deficit.

Conclusions:

• Limb loading asymmetries in natural conditions suggest individuals post-ACLr engage in nonuse behavior, shifting load away from the surgical limb.
• Despite the ability to meet task demands, learned nonuse may contribute to persistent asymmetry.
• While feedback improved symmetry, some asymmetry remained even when instructed to load symmetrically.