Running Specific Prosthesis (RSP) allow amputee sprinters to compare to the best able-bodied sprinters in the world. In RSP research, the current state of the art mainly focusses on highly detailed analysis of discrete moments in the sprint, but more data of the entire sprint process in terms of RSP characteristics and sprinting technique are needed for further development of RSP-design and sprinting technique. In recent research Petrone et al. [4] and Galvão et al. [2] developed instrumented RSPs for collection of Ground Reaction Force (GRF)s suring sprinting, however both methods have disadvantages for implementation of instrumented RSPs in amputee sprinting training purposes. A different instrumented RSP approach was taken in this research by measuring surface strain in Fiber Bragg Grating (FBG) sensors attached to two RSPs; one Ottobock 1E90 and one Gyromotics ArcX Sport. From the collected data the internal moments and axial forces could be approximated, from which the GRF magnitude, direction and point of application were determined. The sensor system was calibrated in a 1-DOF load-cell compression bench and was conducted to a field test in which a participant performed load shifting, walking and running trails on the instrumented Gyromotics RSP. The compression tests showed that the measurement system complied to design requirements and that it was possible to estimate the point of application of the GRF. The field test indicated that loads applied in different directions than applied in the compression bench could lead to measurement errors. Additional calibration, predominantly in the x-direction, is therefore needed.