Walking can be modeled as a motion whereby the center of mass (COM) moves over the stance leg, similar to an inverted pendulum. This inverted pendulum motion requires almost no energy input during the single stance phase due to the efficient interchange between kinetic and potential energy. However, energy input from ankle push-off is needed to redirect the COM from the downward phase of one step to the upward phase of the next step. Previous research found that optimal aiding forces at the COM reduced propulsion at the expense of increasing braking ground reaction forces (GRFs). It was suggested that a future research direction could involve developing devices that allow assisting specifically during propulsion. The aim of the present study was to investigate the effects of different forward force profiles at the COM during walking. We developed a robotic waist tether that allows applying desired cyclic force profiles at the COM as a function of step time from our cable actuation system. We found that both horizontal force profiles that coincided with the propulsion phase as well as force profiles that coincided with the braking phase reduced propulsion GRFs. This type of assistance could be helpful in gait rehabilitation environments for individuals with limited mobility to improve their physical activity levels and increase their walking speed.