This paper investigates the interactive locomotion for physically coupled bipedal agents using a human-human object carrying experiment and a simple mathematical model. The model is based on the Spring Loaded Inverted Pendulum (SLIP) and on the assumption that the coupling can be modeled as a spring-damper. By setting appropriate parameters, the model can achieve stable walking gaits and coordinated foot-fall patterns. Human-human interactive locomotion data are also analyzed in order to evaluate how the model can be useful to investigate humans' interaction. The kinematic study of how the rigid coupling between two humans can influence their own behaviour is presented for the first time to our knowledge. Moreover a good match between experimental and model data emerges from the comparison between several gait parameters.