The goal of this study is to determine short-term adaptations (aftereffects) in knee loading after a 20-minute split-belt treadmill training session in patients with ACL reconstruction.

Our main question for this aim are:

1. Are training-mediated aftereffects in the knee joint moment greater for tied-belt walking or split-belt walking?
2. Are training-mediated aftereffects in the knee joint moment different between subjects who train early stance knee loading versus subjects who train mid-stance knee loading?

Knee and limb underloading are ubiquitous after anterior cruciate ligament (ACL) reconstruction and fails to resolve with the standard of care rehabilitation. This underloading behavior is clinically concerning and considered maladaptive, as it affects patient function, has been linked to risk for re-injury, and appears to be a precursor for post-traumatic knee osteoarthritis that affects upwards of 50% of patients who undergo an ACL reconstruction.

Split-belt treadmill training is a gait retraining approach where treadmill belt speeds are decoupled (i.e., one belt is set to move at a faster or slower speed than the other belt) during walking. Split-belt training is based on well-established motor learning principles, such as error-based learning and variability of practice which can lead to locomotor adaptations. In healthy individuals, split-belt treadmill walking significantly increases knee moment impulses in the limb on the slow belt than on the fast belt during the braking and propulsive phases of gait. Split-belt treadmill training has also shown promise in individuals with neurological deficits, resulting in significant improvements in gait biomechanics after training.

The aim of this project is to determine short-term adaptations (aftereffects) in knee loading after a 20-minute split-belt treadmill training session in individuals with anterior cruciate ligament (ACL) reconstruction. Individuals ~6-10 months after ACL reconstruction will be randomly assigned to 1 of 2 groups and each group will complete a split-belt and tied-belt session. One group will train the early stance knee moment with split-belt walking, while the other group will train the mid-stance knee moment with split-belt walking. Both groups will also complete a tied-belt session. Bilateral knee loading will be quantified using peak knee moments before training (10 min), during training (20 min), and after training (10 min). The investigators hypothesize that the training-mediated aftereffects (i.e., loading after training) will be significantly higher in the split-belt condition than in the tied-belt control condition. The investigators also hypothesize that early stance split-belt training will lead to training-mediated aftereffects for the early stance moment only, while mid-stance training will only result in aftereffects for the mid-stance knee moment.

Inclusion Criteria:

• aged 14-45 years
• suffered an acute, complete ACL rupture as confirmed by MRI and physical exam
• have undergone ACL reconstruction w autograft within the past 10 months
• willingness to participate in testing and follow-up as outlined in the protocol
• English-speaking

Exclusion Criteria:

• inability to provide written informed consent
• female subjects who are pregnant or are planning to become pregnant (self-reported)
• previous ACL injury
• previous surgery to either knee
• bony fracture accompanying ACL injury
• patients who experienced a knee dislocation
• patients who had their ACL reconstructed with an allograft
• patients who underwent a multi-ligamentous and/or staged ACL reconstruction

De-identified data will be made publicly available via Deep Blue Data which is managed by the University of Michigan.

We will strive to release data to the repository as rapidly as it is possible to analyze experiments and publish results. Data used in publications will be released at the time of publication.