## 1 Introduction
Moreover, such a biomechanical model is individual-specific and based on measurements obtained from scans of each user, e.g., magnetic resonance imaging scans, to take into account the conditions of each individual's residual limb and prosthetic socket. Therefore, the generated biomechanical model would not be generalizable, making this method relatively complex and expensive. Alternative methods using relatively accurate force sensors, such as load cells, for registering the pressure map at the interface of the prosthetic socket and the residual limb, which can be used towards the goal of this study, have also been investigated. [PERSON] et al. investigated this method in a study where they measured the interface pressure using 13 transducers mounted on the users' prosthetic sockets to investigate the interface pressures as socket fit was adjusted with fluid filled inserts [21]. Although the measurements obtained by such transducers can be used to determine and adjust the quality of the socket fit, these sensors are relatively expensive, not flexible, and difficult to incorporate in prosthetic sockets as modifications to the socket are required to mount the sensors. As reported in the study by [PERSON] et al., the transducers used in their investigations added 320 g to the system, which is another disadvantage of using such sensors for everyday use of this application. Force sensitive resistors (FSRs) are alternative solutions for prosthetic applications. The use of FSR-based sensory systems for acquisition of pressure maps at the interface of the residual limb and the prosthetic socket has been explored.Portnoy et al. investigated the use of FSRs for analysis of residual limb stresses [18]. In their study, measurements acquired from FSRs were used as boundary conditions for finite element analysis of stresses. Although this method utilized FSRs that are thin, flexible, easy to place inside the socket, and could potentially assist users with managing their limb volume adjustment system, it required additional data from X-rays and indentation tests to determine dimensions of the bones and soft tissues and elastic modulus of soft tissues, which makes the method relatively complex and costly. The motivation behind this study was to develop a simple, inexpensive method that can determine fluctuations in the volume of the residual limb with the ultimate goal of using this information to assist users with the management of their volume adjustment system to prevent skin health problems that are caused by an inadequate fit of the prosthetic socket. Towards this goal, the study presented in this paper proposes an alternative method for determining variations in the volume of the limb through monitoring distal forces with a limited number of FSRs at the bottom of the socket. The proposed method is simple, easy to incorporate into the socket, and inexpensive. Furthermore, it does not require modifications to the socket and does not rely on electrical contact with the skin or information from X-rays or indentation tests. The study presented in this paper demonstrates the feasibility of detecting variations in the volume of the limb using the proposed method and identified the locations at the bottom of the socket at which the variations of pressure would be representative of the changes in the volume of the limb.