*2.1. Data Collection*

We conducted two data collection studies for algorithm comparison, a lab study and a field study. The lab study was conducted in a sports research lab to evaluate the performance of the algorithms against ground-truth stride length and velocity labels on a per stride basis. A 3D motion tracking system was used as a reference. The field study was conducted on a 400-m outdoor running track to evaluate the performance regarding the total distance on a continuous 3.2-km run in realistic free-running conditions. The track length was used as a reference.
