That wheelchair user’s shoulder joint injuries are directly related to poor wheelchair design and the location of the wheelchair driving mechanism has been proven clinically. This work presents a novel approach to rapidly customize the design of manual wheelchairs, such that each user can easily obtain a custom manual wheelchair, thereby reducing the potential for shoulder joint injury. In this study, a human-chair system composed of a human body and a wheelchair was simulated as a plain single-loop five-bar linkage. Mobility analysis was conducted to identify the corresponding joint workspace. By analyzing linkage movement and the upper-limb muscle strength of a user, the optimal location of the wheel hub and optimal radius of the handwheel were identified as the bases of a customized design for manual wheelchairs.