Passive stiffness of the hamstrings and the rectus femoris in persons after an ACL reconstruction

Objectives: The aim of the article is to investigate the passive stiffness (PS) of rectus femoris and hamstring muscles working for the knee joint in persons after anterior cruciate ligament (ACL) reconstruction surgery. Methods: Thirty subjects (8 women and 22 men) aged 19-46 (x = 28.2 +/- 7) participated in the investigation; an experimental group comprised 15 persons (4 women and 11 men) who underwent ACL reconstruction surgery. The other persons had no knee injury and described themselves as healthy. All the subjects underwent an investigation of the PS of the hamstrings and the rectus femoris on the injured as well as on the healthy leg. Results: The data shows vital difference in the PS of the hamstring muscles between the healthy and injured limb (p < 0.05), a significant difference in the PS of the rectus femoris (p < 0.001) was noted. Furthermore, the PS level of the hamstring muscles of the operated limb in the experimental group is significantly different to the both legs in control group (p < 0.001). Conclusions: Injury of the ACL results in a considerable increase in passive stiffness of the hamstring and rectus femoris muscles in both the injured leg and the healthy leg.