Before revision:  In vivo myosin-V activity generates a forceof F \sim 0.4 pN, with a power-stroke of length \Delta x \sim 20 nm and duration \tau \sim 300 \mus , that drives vesicle motion at v_v \sim 320 nm/s. This framework is widely applicable to quantify nonequilibrium properties of living cells and other soft active materials .
After revision:  In vivo myosin-V activity generates a forceof F \sim 0.4 pN, with a power-stroke of length \Delta x \sim 20 nm and duration \tau \sim 300 \mus resulting in an average force of F \sim 0.4 pN on vesicles. Our results reveal that measuring in-vivo active fluctuations allows extraction of the underlying molecular motor activity and demonstrates a widely applicable mesoscopic framework to access molecular-scale force kinetics .