Why forefoot striking in minimal shoes might positively change the course of running injuries

Short- and long-term effects of altered point of ground reaction force application on human running energetics

The current study investigates an acute and a gradual transition of the point of force application (PFA) from the rearfoot towards the fore of the foot during running, on the rate of metabolic energy consumption. The participants were randomly assigned in two experimental and one control groups: a short-term intervention group (STI, N=17; two training sessions), a long-term intervention group (LTI, N=10; 14-week gradual transition) and a control group (CG, N=11). Data were collected at two running velocities (2.5 and 3.0 m/s). The cost coefficient (i.e. energy required for a unit of vertical ground reaction force, J/N) decreased (p<0.001) after both interventions due to a more anterior PFA during running (STI:12%, LTI:11%), but led to a higher (p<0.001) rate of force generation (STI:17%, LTI:15.2%). Dynamic stability of running showed a significant (p<0.001) decrease in the STI (2.1%), but no differences (p=0.673) in the LTI. The rate of metabolic energy consumption increased in the STI (p=0.038), but remained unchanged in the LTI (p=0.660). The control group had no changes. These results demonstrate that the cost coefficient was successfully decreased following an alteration in the running technique towards a more anterior PFA. However, the energy consumption remained unchanged because of a simultaneous increase in rate of force generation due to a decreased contact time per step. The increased instability found during the short-term intervention and its neutralization after the long-term intervention indicates a role of motor control errors in the economy of running after acute alterations in habitual running execution.