Lower extremity joint stiffness in runners with low back pain.

The purpose of this retrospective study was to examine lower extremity joint stiffness between runners with and without low back pain. We compared data from three groups: current low back pain (LBP), resolved pain (RES), and a control (CTRL) group of runners. We hypothesized that the LBP group would exhibit increased ankle, knee, and hip joint stiffness when compared with the other groups. Subjects ran on a force treadmill at 3.8 m*s(-1) while data were collected. Joint stiffness was determined from the joint moment-angle profiles. Differences were observed in knee joint stiffness, with the LBP group exhibiting the greatest stiffness values. No differences in ankle or hip joint stiffness were observed. These data suggest that the LBP group of runners may not attenuate the foot-ground impact to the same level as the other groups. The decreased attenuation may increase the level of the shock to the low back region, thus potentially increasing the load on the low back.