Changes in Passive Hamstring Stiffness after Primary Anterior Cruciate Ligament Reconstruction: A Prospective Study with Comparison of Healthy Controls.

•Knee flexors stiffness help reducing anterior cruciate ligament loading.•Passive stiffness was investigated after anterior cruciate ligament reconstruction.•The operated leg experienced lower stiffness than the non-operated leg after surgery.•Both legs had lower stiffness comparing healthy controls.•There was no significant increased stiffness in individuals with extension deficit.