Runners: Beware the Downhill

Distance runners frequently run up and down hills while training and racing.

Does running up or down hill change knee stress? Should runners experiencing knee issues take any special precautions when running up or down hill? A recent study examined those questions.

Runners were tested on a treadmill at 3, 6 and 9 degrees uphill and 3,6 and 9 degrees downhill. Runners were also tested on level ground.

Going uphill? No problem. In fact, impact peaks actually decreased when the runners went uphill largely due to changed foot-strike patterns.

Downhill was another story.

At just a 3 degree decline, impact peaks increased by 18% and parallel braking forces increased by 27% compared to level running.

At six degrees decline, impact forces increased by 32% and parallel braking forces increased by 46%.

At nine degrees decline, impact forces increased by 54% and parallel braking forces increased by 73%.

A previous study (Hreljac 2000) had noted higher impact peaks were the primary distinction between injured runners and never injured runners. In fact, Hreljac found injured runners had a 13% higher impact peak than non-injured runners. As noted above, even a 3 degree decline produces 18% higher impact peaks than level running.

If you must run downhill, this study notes greater bend at the knee when landing (termed flexion) and a shorter stride can lower the impact peaks sustained at the knee.

If you are experiencing knee problems, it is advisable to avoid hills completely.

Gottschall JS, Kram R, Ground Reaction Forces During Downhill Running, Journal of Biomechanics 38 (2005)445-452.