As the Surf Coast Century is rapidly approaching, and the popularity of trail running is increasing, we thought we’d give a brief run down on downhill running. There are plenty of hills along the course that many will be tackling this weekend, and if you haven’t done much downhill running…be prepared to pull up a little more sore than usual!
DOWNHILL RUNNING & INJURY
Downhill running results in a marked increase in impact force peaks. We experience greater braking forces when running downhill, as opposed to the propulsive forces we experience with running uphill.
Impact force peaks have been associated with an increased risk of musculoskeletal injury. The data regarding downhill running, therefore suggests that there is an increased risk of injury with downhill running, and a reduced risk with uphill running.
Along with an increase in impact force peaks, a rearfoot strike pattern is commonly observed when running downhill. This strike pattern is associated with greater knee loads, we can therefore hypothesis that the risk of knee injury may increase with downhill running.
One study (Hreljac et al., 2000) looked at a group of injured and non-injured runners and compared impact force peak data. They found that impact force peaks were 13% greater in the injured group than the non-injured. A difference of 13% is equivalent to the increase observed with running at an angle of -3 degrees.
Impact forces can be moderated by changing running variables such as knee flexion angle at foot strike and stride length. This suggests that reducing stride length whilst running downhill may reduce impact force peaks and reduce risk of injury.
DOWNHILL RUNNING AND “COST”
In regards to the “cost” of running. There is a reduced metabolic cost associated with downhill running, this explains why many find downhill running to be a reprieve from an energy consumption perspective. The concentric muscle contractions during propulsive uphill running are more expensive than the eccentric muscle contractions required by the braking forces of downhill running.
Eccentric muscle activation is the controlled lengthening of muscle tissue under tension. The muscle groups that experience the greatest increase in eccentric demand during downhill running are the knee extensors (quads), hip extensors (glutes) and muscles in both anterior and posterior compartments of the lower leg.
Whilst downhill running might not come at the same metabolic cost, the eccentric muscle activation required has been shown to result in greater mechanical muscle damage. This can result in post-exercise soreness & DOMS.
Studies have shown that the mechanisms producing muscle damage after level endurance running and downhill running were not the same. The changes to muscle tissue after level endurance running are more metabolic, as opposed to mechanical which is observed after downhill running.
So, if you haven’t been running many hills and are headed out for a hilly run, prepare to be a little more sore (and experience a reduction in strength of primarily quads and glutes). If you’ve been running hills, you’re muscles will have been adapting to the eccentric demand required from downhill running and are far less likely to respond with soreness, weakness and fatigue.
If you’re currently in the grips of an injury (especially knee; hip; ankle), be careful on the downhill. Adjusting your technique may be of benefit in both the management and prevention of injury.