The concurrent validity of a portable force plate system for measuring isometric mid-thigh pull

The increasing availability of portable force plates with automated analysis software has made measuring the isometric mid-thigh pull (IMTP) more convenient and efficient. It is essential for practical application to validate the portable force plate systems (FPSs) for the IMTP measurement. This study aims to examine the concurrent validity of portable FPSs. We simultaneously collected vertical ground reaction force (vGRF) during the IMTP using two portable FPSs (ForceIntellec and ForceDecks) and a ground-based FPS (Kistler), and the vGRF were analyzed using the proprietary software associated with each FPS. The results demonstrated good consistency between portable and ground-based FPSs, with all metrics exhibited low differences (<5%) along with minor proportional bias in peak force (PF), net PF, and some intervals of rate of force developments (RFDs). Furthermore, no systematic or proportional bias was observed between portable FPSs in PF, net PF, and force impulses (FIs), but all intervals of RFDs showed inconsistencies. Overall, portable FPSs are valid tools for the IMTP measurement. However, due to observed inconsistencies in RFDs, it is recommended to prioritize the use of FIs when employing different FPSs. These findings contribute to the broader goal of validating FPSs, enhancing their utility in research and practice.