Although inter-and intra-tester reliability has been a common theme in Functional Movement Screen (FMS) research, the criterion validity of manual grading is yet to be comprehensively examined. This study aimed to compare the FMS scores assigned by a certified FMS tester to those measured by an objective inertial-based motion capture system (IMU). Eleven female Division I collegiate athletes performed six FMS exercises and were manually graded by a tester. Explicit kinematic thresholds were formulated to correspond to each of the grading criteria for each FMS exercise and then used to grade athletes objectively using the IMU data. The levels of agreement between the two grading methods were poor in all six FMS exercises. It appears that manual grading of the FMS is confounded by vague grading criteria. More explicit grading guidelines would likely improve the uniformity and accuracy of manual FMS grading and also facilitate the use of objective measurement systems in the grading process. Contrary to the approach that has been employed in several previous studies, the potential for subjective and/or inaccurate FMS grading insinuates that it may be inappropriate to assume that manual FMS grading provides a valid measurement tool. Consequently, the development and criterion validation of uniform grading procedures must precede research attempting to link FMS performance and injury rates. With manual grading methods seemingly susceptible to error, the FMS should be used cautiously to direct strength and/or conditioning programs.
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