This study focuses on determining the effects of the upper material of running shoes on the mechanical power flows of the muscles of the lower limbs during the support phase of running. Two models of running shoes¿differentiated only by the upper structure and material¿have been used, being randomly assigned to 19 participants. Five measure- ments of each participant per shoe model were obtained at 3.3 m s 1 to perform inverse dynamic analysis with the data obtained. Statistically significant differences have been found between the two models for the muscle power flow variables in the ankle, knee and hip joints, as well as at the ends of adjacent segments. The KNIT-upper model (model 2) presents higher generation (8.87 ± 7.63 W/kg; p < .001; d = -.13) and less absorption ( 5.11 W/kg; p < .001; d = 6.7) of mechanical power in the ankle compared to the MESH-upper model (model 1). The mechanical power flows in the knee and hip indicate that with model 2, greater mechanical power is generated and absorbed by the flexor and extensor muscle groups of these joints compared to model 1 (-.38 ± 2.9 W/kg vs -.22 ± 2.54 W/kg for the knee and 1.75 ± 2.91 W/kg vs 1.15 ± 2.07 W/kg for the hip, respectively). Therefore, it can be concluded that the upper material has an influence on mechanical power flow patterns. However, more studies are needed in order to ac- curately and reliably establish the impact that the upper material of the shoes has on performance and on the prevention of sports injuries.