Our research program examined the performance variations in custom FOs and the influence of inter-practitioner variability in assessing their effectiveness. The results showed that practitioner differences are a major factor influencing FO performance in treating a patient for a specific pathology. Thus, caution is warranted when generalizing FO effects from one study to another or across practitioners, as the conclusions could vastly differ. As part of examining the lack of systematic results on FO influences on lower limb kinematics, we found that FOs seem to have generic effects in controlling rearfoot pronation but that variations in the research design and between-practitioner differences can lead to inconsistent findings. We provided recommendations for standardizing future FO research to better enable comparisons between studies and improve the understanding of how FO variables might impact treatment outcomes. Our previous work established the effects of simple flat-based insoles on 3D foot motion and provided a philosophically justifiable definition of pronation. Moving forward, further examination into the mechanisms of how custom FOs work and additional standardization of FO research methods, including accounting for practitioner-related variability, will help produce more generalizable results.  In addition to experimental work, we have also provided a philosophically justifiable definition of pronation.