The study investigates the relationship between force and focal complex development in cells. Cells must apply cytoskeletal force to the extracellular matrix (ECM) through integrin receptors to adhere and migrate. The research focuses on whether initial integrin-ECM adhesions can immediately exert migration force or if adhesion maturation is necessary for force transmission. The authors show that initial integrin-ECM adhesions can become capable of exerting migration force when they recruit vinculin, a marker for focal complexes, which are precursors of focal adhesions. They induce the development of focal complexes by applying mechanical force to fibronectin receptors from inside or outside the cell and extend this to vitronectin receptors by removing c-Src. These findings indicate that cells use mechanical force as a signal to strengthen initial integrin-ECM adhesions into focal complexes and regulate the amount of migration force applied to individual adhesions at localized regions of the advancing lamella. The study also demonstrates that focal complexes formed at the leading edge of a motile cell exert smaller forces than those exerted by focal adhesions, and these forces do not decrease as the complex enlarges and travels rearward on the lamella.The study investigates the relationship between force and focal complex development in cells. Cells must apply cytoskeletal force to the extracellular matrix (ECM) through integrin receptors to adhere and migrate. The research focuses on whether initial integrin-ECM adhesions can immediately exert migration force or if adhesion maturation is necessary for force transmission. The authors show that initial integrin-ECM adhesions can become capable of exerting migration force when they recruit vinculin, a marker for focal complexes, which are precursors of focal adhesions. They induce the development of focal complexes by applying mechanical force to fibronectin receptors from inside or outside the cell and extend this to vitronectin receptors by removing c-Src. These findings indicate that cells use mechanical force as a signal to strengthen initial integrin-ECM adhesions into focal complexes and regulate the amount of migration force applied to individual adhesions at localized regions of the advancing lamella. The study also demonstrates that focal complexes formed at the leading edge of a motile cell exert smaller forces than those exerted by focal adhesions, and these forces do not decrease as the complex enlarges and travels rearward on the lamella.