Figure A1.

Strategy used to deal with phase shifts between motion capture and IMU acquisition clocks. A TTL output was emitted for one out of six video frames (mocap frame 0, light gray). The rising front of this TTL signal was detected by the IMU acquisition board and used to timestamp the corresponding IMU sample (IMU frame 0, dark gray). Small clock irregularities could result in a jump one IMU sample forward or backward of the timestamp (purple arrowhead in cases 2 and 3, observed for 0.07% of the synchronization cycles). These cases were dealt with by duplicating or deleting the last mocap sample of the corresponding synchronization cycle.