In actin polymerization-based membrane protrusions, the velocity of the protruding membrane decreases with increasing opposing force. This relationship, known as the force-velocity relation (FVR), can be concave up or concave down. However, the mechanism by which FVR exhibits two trends remains debatable. In this study, we simulate the Brownian dynamics of the protruding membrane driven by actin polymerization. The actin diffusion coefficient is retained constant, and the actin polymerization rates are set to low (case-L) or high (case-H). The protruding membrane in the case-L and case-H simulations exhibits a concave up and concave down FVR, respectively. The polymerization rate affects the spatial distribution of actins, and thereby their physical contact with the membrane. The membrane is predominantly sustained by monomers in case-L and filaments in case-H. This suggests that membrane protrusions respond differently to the opposing force because actins are differently distributed around the membrane.