What is it about?
There is a growing body of evidence documenting loads applied to the anterior cruciate ligament (ACL) for weight bearing (WB) and non-weight bearing (NWB) exercises. ACL loading has been quantified by inverse dynamics techniques that measure anterior shear force at the tibiofemoral joint (net force primarily restrained by the ACL), ACL strain (defined as change in ACL length with respect to original length, and expressed as a percent) measured directly in vivo, and ACL tensile force estimated through mathematical modeling and computer optimization techniques. A review of the biomechanical literature indicates that ACL loading is generally greater with NWB compared to WB exercises, that for both types of exercises, the ACL is loaded to a greater extent between 10 to 50º of knee flexion (generally peaking between 10-30º) compared to 50 to 100º knee flexion, and that loads on the ACL change according to exercise technique (such as trunk position). Squatting with excessive forward movement of the knees beyond the toes and with the heels off the ground tend to increase ACL loading. Squatting and lunging with a forward trunk tilt tend to decrease ACL loading likely due to increased hamstrings activity. During seated knee extension, ACL force decreases when the resistance pad is positioned more proximal on the anterior aspect of the lower leg, away from the ankle. The evidence reviewed as part of this manuscript provides objective data to rank exercises based on loading applied to the ACL. The biggest challenge in exercise selection post-ACL reconstruction is the limited knowledge of the optimal amount of stress that should be applied to the ACL graft as it goes through its initial incorporation and eventual maturation process.
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Why is it important?
Clinicians may utilize this review as a guide to exercise selection and rehabilitation progression for patients post ACL reconstruction.
Perspectives
The goal of rehabilitation of patients post ACL reconstruction is to resolve impairments such as swelling, pain, and lack of range of motion and to normalize lower extremity muscle strength and dynamic stability without interfering with the healing process of the graft. Understanding how the ACL is loaded during rehabilitation can help clinicians better prescribe training and exercise regimens in a safe manner, enhance and possibly expedite the rehabilitation process, and return the athlete to sport or activity. Therefore, the purpose of this paper is to discuss the biomechanical factors related to ACL loading during common WB and NWB exercises performed during ACL rehabilitation. Clinicians may utilize this review as a guide to exercise selection and progression for patients with ACL pathology or reconstruction.
Rafael Escamilla
California State University, Sacramento
Read the Original
This page is a summary of: ACL Strain and Tensile Forces for Weight Bearing and Non—Weight-Bearing Exercises After ACL Reconstruction: A Guide to Exercise Selection, Journal of Orthopaedic and Sports Physical Therapy, March 2012, Journal of Orthopaedic & Sports Physical Therapy (JOSPT),
DOI: 10.2519/jospt.2012.3768.
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