Instrument-assisted soft tissue mobilization (IASTM) techniques use specialized hand-held instruments for applying controlled mechanical forces to the body with the goal of facilitating healing, improving range of motion, and reducing pain. Nevertheless, an optimal range of forces for achieving clinical outcomes has yet to be established. A barrier to advancing research on IASTM force optimization is the lack of commercially available instruments that quantify treatment forces. The aim of the current study was to assess the feasibility of attaching a flexible force sensor to a commercially available IASTM instrument to obtain valid force measurements. The validity of this novel approach was assessed by comparing data between the flexible force sensor and a force plate during a simulated treatment. Intraclass correlation coefficients, linear regression models, and Bland Altman plots all indicated excellent agreement between the force plate and flexible sensor when the instrument was used at 45°, 65°, and 90° treatment angles. Agreement between measures decreased when the instrument was held at 30°. Thus, commercially available instruments with attached sensors could make force measurement more accessible and feasible for a wider range of research settings, facilitating the advancement of IASTM research and ultimately informing clinical decision-making to improve patient care.