**5. Conclusions**

This study documents the high accuracy of IMU-derived lower limb joint angles during walking using several functional movements for the sensor-to-segment calibration. Functional movements requiring larger segmental angular amplitudes provided more accurate segmental reference frames and led to a higher accuracy regarding the kinematics of the adjacent joints. Alternatively, the higher linear accelerations generated at distal segments during a walking functional calibration also led to a higher reproducibility for distal joints, in comparison to the functional calibration based on the principal rotational axes. The walking, tilted, and extension functional calibration movements were shown to be three equivalent options for the gait movement examined in this study. In addition, for examining walking, the walking functional calibration may be superior because it involved very limited material and instruction complexity, which strengthens its interest in uncontrolled environments.

**Author Contributions:** Conceptualization, J.L., T.G., C.D., O.C., and M.P.; data curation, J.L.; formal analysis, J.L.; funding acquisition, C.D.; investigation, J.L. and T.G.; methodology, J.L., T.G., C.D., O.C., and M.P.; project administration, J.L., C.D., and M.P.; resources, J.L., C.D., and M.P.; software, J.L. and T.G.; supervision, C.D., O.C., and M.P.; validation, J.L., T.G., C.D., P.M., O.C., and M.P.; visualization, J.L., T.G., and M.P.; writing—original draft, J.L. and M.P.; Writing—review and editing, J.L., T.G., C.D., P.M., and M.P. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** We wish to express our gratitude to Julie Lamsens and Guillaume Gaudet for proofreading the paper.

**Conflicts of Interest:** The authors declare no conflict of interest.
