Brief summary, from the abstract
In a lab study of healthy volunteers, a 10 kg loaded open-kinetic-chain knee extension stretched the ACL the most of the exercises tested, while an unloaded knee extension stretched it the least, suggesting unloaded open-chain work may be gentler on the graft early after ACL reconstruction.
- Eighteen healthy volunteers performed two open-kinetic-chain motions (unloaded and 10 kg loaded seated knee extension) and two closed-kinetic-chain motions (box squat and deep single-leg lunge), with ACL length tracked via 2D-to-3D image registration and 3D ligament simulation.
- The loaded knee extension (OKC-10) lengthened both ACL bundles significantly more than the unloaded version (OKC-0) across 0 to 60 degrees and 0 to 55 degrees of knee flexion (p < 0.01); box squat and lunge showed no significant difference from each other.
- Relative to reference length, OKC-10 stretched the anteromedial bundle from 0 to 30 degrees and the posterolateral bundle from 0 to 10 degrees, while closed-chain exercises stretched them from 0 to 25 degrees and 0 to 5 degrees.
- Evidence is from a single small descriptive laboratory study in healthy volunteers, not surgical patients, so it informs biomechanical reasoning rather than confirming clinical outcomes; the authors suggest loaded exercises be restricted to beyond 30 degrees of flexion in early-stage rehab.
Clinically assessing this area? See the knee special tests.