Joint stiffness and back pain

Some researchers have hypothesised that lower limb joint stiffness can be a contributing factor to low back pain because it alters running biomechanics, placing additional loading on the back.

To test this theory, US researchers have investigated lower extremity joint stiffness in runners with and without low back pain. To do this, they compared data from three groups of runners:

• Those with current low back pain (LBP);
• Those with resolved low back pain (RES).

Subjects ran at 8.5mph on a ‘force treadmill’ – a specially adapted treadmill designed to measure the vertical, horizontal and lateral components of the ground-reaction impact forces during running. Data on these forces were collected during running and joint stiffness was determined from the joint moment/angle profiles.

The results showed no differences in ankle or hip joint stiffness; however, in the group with lower back pain, knee stiffness was significantly higher. Increased knee joint stiffness is associated with less ‘give’ on each foot strike; the researchers surmised that their findings suggest that the LBP group of runners were not able to attenuate the foot-ground impact to the same level as the other groups and that this decreased attenuation could increase the level of the shock to the low back region, thus potentially increasing the load on the low back.

Res Sports Med. 2009;17(4):260-73