Clathrin-mediated endocytosis is a conserved process by which eukaryotic cells take up molecules from their environment. Endocytic membrane bending in budding yeast requires the construction of a dynamic actin network, which produces force to deform the plasma membrane against the turgor pressure. The type-I myosins Myo3 and Myo5 are essential for endocytosis, but how they contribute to remains unknown. The goal of my PhD thesis was to investigate these proteins to clarify their role in endocytosis in yeast. Using quantitative live cell imaging and genetic perturbations, I show that Myo3 and Myo5 stimulate actin network growth in a dose-dependent way, which controls the speed of coat movement. This ability does not depend on their Arp2/3-activating domain. Together, these findings refine our understanding of the role that Myo3 and Myo5 play within the endocytic machinery and suggest a novel role for type-I myosins in facilitating actin network growth under high loads.