This paper presents an in-depth analysis of a U-shaped assembly cell using flexible skilled walking workers. The study was based on the design of a linear assembly line using the similar walking worker approach. In this paper, the authors illustrate a mathematical model that was developed to describe the mechanism of this type of U-shaped walking worker assembly cell, which has been seen in industry. The mathematical model also incorporates two major scenarios in terms of human performance variation providing an insight into such a dynamic, flexible and reconfigurable assembly system.