Optotrak cameras

A total of sixteen markers were attached to the skin (right side) to the pre-palpated anatomical landmarks, marked with a pencil by an experienced physiotherapist and four markers were attached to the custom-made station Figure 1. Three custom-made spinal-clusters were positioned at the sacrum, 9^th thoracic spinous process, and 4^th thoracic spinous process. All markers were fixated to the skin by double-sided adhesive tape. All cluster-markers were additionally supported by an elastic band (Fabrifoam^®) and Fixomull®strech tape (BSN Medical). The three-dimensional positions of the markers were determined with an accuracy of up to 0.1 mm and resolution of 0.01 mm utilizing three Optotrak^® cameras (Northern Digital Inc.) (Schmidt et al., 2009 (link)) at a sampling rate of 100 Hz. The data was sampled for 15 s. The three Optotrak^® cameras were set in an arch and calibrated/aligned towards the station’s right-sagittal side (Supplementary Material).

Full body kinematics were measured using two Optotrak cameras (Northern Digital Inc, Waterloo Ontario, Canada) directed at the center of the treadmill (sampling rate was 50 Hz). Cluster markers were attached to the feet, shanks, thighs, pelvis, trunk, upper arms and forearms. Corresponding anatomical landmarks were digitized using a six-marker probe.

Participants’ movements were tracked by seven synchronized Optotrak® cameras (Northern Digital, NDI, Waterloo, Ontario): three lateral cameras on each side of the runway (vertically oriented) and one central camera (vertically oriented) 2.5 m away from the end of the runway. These cameras tracked the entire runway (~10 m). Active IREDs (infrared light emitting diodes) were fixed to the following anatomical regions: midpoint between the iliac crests (defined by the umbilicus), lateral malleolus, and 5^th metatarsals. Heel contacts and toe offs were visually defined using a validated method [23 (link)]. The heel contact and toe off kinematics were used to calculate gait variables during the approach and crossing phases. All kinematic data were filtered using a 2^nd order Butterworth filter with a cut-off frequency of 6 Hz using a dual-pass filter with zero lag delay. Kinematic variables were calculated using an algorithm created in Matlab 7.0 (The Maths Works Inc.), RRID:nlx_153890.