“We are our choices” – Jean-Paul Sartre.
The varied and unpredictable surfaces and inclines of trails impose unique and extreme demands on the runner. Injury rates as high as 90% have been reported, with higher standard and greater experience being linked to injury incidence. The lower back, lower leg and foot are the most common injury sites (Malliaropoulus et al., 2015).
Choosing the right movement gear
Skilled trail runners adapt gait with slope and terrain, choosing a forefoot strike with shorter, faster strides uphill, and a heel strike with longer and slower strides downhill (Giandolini et al., 2015). Varying strike type, stride length and frequency provides a mechanism to minimise the energy cost of generating the different forces needed for running uphill and downhill. In essence, skilled trail runners change gear to maximise the efficiency of muscle force production, in the same way as we change gear in a car to maximise the efficiency of engine power production (Carrier et al., 1994). A quick forefoot strike (high gear) maximises use of elastic energy, generating the propulsive forces required to raise body mass uphill with the least energy (Gottschall and Kram, 2005). A long stride with a heel strike (low gear) is the most energy-efficient means to generate the high braking forces required control descent in downhill running (Pratt, 1989).
Choosing the right foot gear
High-gear (forefoot) running places great demands on the forefoot and lower leg. Lower limb and metatarsal injuries are common (Daoud et al., 2012). A shoe providing forefoot stability and cushioning is crucial to reduce metatarsal loads and compensatory action of lower leg muscles. Low-gear (rearfoot) running produces large impact forces and predisposes the heel, hip and lower back to impact-related injury (Daoud et al., 2012). A shoe providing adequate rearfoot cushioning is crucial to dampen these forces.
Trail running is a demanding sport with high rates of injury. Reducing injury risk requires the correct choice of movement gear for uphill (high gear) and downhill (low gear) running and the correct choice of foot gear to protect the runner from the biomechanical consequences of the movement gear choice.