Forerunner 945

To collect the necessary raw data, two inertial sensors were used (SpoSens 2.0, Wille Engineering, Germany). The sensors had a size of 77.5 × 37 × 34.5 mm and weighed 45 g each. They functioned as a triaxial accelerometer with up to 400 G (16 G was used), a triaxial Gyroscope with up to 2000°s (maximum was used) and a magnetometer measuring with up to 16 Gauss (maximum was used). The possible sampling rate could be set up to 1.000 Hz (250 Hz was used) and they were constructed as a micro-electro-mechanical system (MEMS). Further, the sensors were equipped with GNSS (max. 5 Hz) technology. They collected and saved the running motion data in three dimensions (x, y, z) on an internal storage device (8192 GB). The sensors were attached to both ankles above each lateral malleolus by a hook-and-loop fastener. All data were received and stored on a GARMIN Forerunner 945 (GARMIN, Schaffhausen, Switzerland) during the entire test session. Earlobe blood samples (each of 10 µl) were analyzed for lactate concentration using a stationary laboratory device (HITADO Super GL compact). Body weight, body fat percentage and active muscle mass (required for the INSCYD analysis) were measured with a Tanita BC-545N body analysis scale (Tanita Europe B.V., Stuttgart, Germany).

Each participant was equipped with a smart patch, three Dytran 7300A5 (MEMS) uniaxial variable-capacitance accelerometers positioned perpendicular to each other (sensitivity: 80 mV/g, range: 50 g, mass: 12 g, Dytran Instruments Inc, Chatsworth, CA, USA), two reflective markers on each foot, and Garmin Running Dynamics Pod (Olathe, KS, USA). The smart patch, Dytran MEMS accelerometers, and Garmin Running Dynamics Pods were placed in the lower lumbar region, while two reflective markers were placed in the front part of the participants’ shoes (one on the right shoe and one on the left shoe). The markers were recorded by an infrared (kinematic) motion capture system consisting of 6 Oqus cameras (Oqus 7+, Qualisys, Gothenburg, Sweden). In addition, all measurements were obtained while running in place on bilateral force plates (S2P, Science to Practice Ltd., Ljubljana, Slovenia), see Figure 1.
Dytran accelerometers and S2P bilateral force plates were wired to two synchronized 24-bit Dewe-43 analogue-to-digital converters and DewesoftX data acquisition software (Dewesoft d.o.o., Trbovlje, Slovenia). The Oqus cameras were connected to Qualisys Track Manager (QTM, Qualisys, Gothenburg, Sweden), the Garmin Running Dynamic Pod was connected to a Garmin Forerunner 945, and a smart patch was connected to a custom Windows application (Bio2BITWinApp, STMicroelectronics, Milan, Italy).