Gaitrite

Participants walked for 2 minutes at a comfortable pace around a 25-m circuit inclusive of a 7 × 0.6m instrumented walkway (Platinum model GaitRite, CIR systems Inc, USA; Supplementary Figure 1). Gait assessment was completed under single task (ST) for which participants were asked to “concentrate on their walking” and dual task (DT) where participants were asked to “concentrate equally on their walking and a concurrent task”. The Wechsler Forward Digit Span was adopted as the concurrent task; a validated working memory task tailored to individual performance. Maximum digit span was first assessed in sitting, determined by longest span recalled in two of three attempts. Participants then recalled continuous strings of their maximum digit span while walking (13 (link)).
Gait outcomes were derived from a model of gait developed in older adults (14 (link)) and validated in PD (15 (link)). The model describes 16 discrete gait characteristics representing domains of pace, rhythm, variability, asymmetry, and postural control (Supplementary Figure 1).

Spatiotemporal parameters were obtained by a research physical therapist (AE) from the GAITRite® (CIR Systems, Franklin NY) electronic walkway in the ON and OFF states with and without a dual cognitive task. The dual tasks alternated between serial 7’s and every other letter of the alphabet. Performance on the dual task was monitored to ensure adequate effort as reported in prior studies [25 (link)]. Spatiotemporal data was collected and averaged from four passes over the GAITRite® walkway (two trials). Specifically, they were asked to stand up, walk over the GAITRite® walkway, step off the GAITRite® onto the M² walkway, turn around a cone set at the center of the M² (54 inches to the center of the cone from the leading edge of the M2/GAITRite® interface), and walk back to the chair. The M² walkway is a square digital walkway placed at the end of the GAITRite® walkway designed to capture the turn. The instructions for the walking task were identical to what is commonplace during the TUG [26 (link)]. The turn was 180° and the diameter of the turn was only limited to the 48″ width or lateral boundaries of the M² walkway. The turn was performed by each subject in their preferred direction. Participants were not required to pre-select their direction of turn and were not mandated to turn in either or both directions.

Gait performance was investigated using a pressure-sensitive sensor carpet (6.7 m, GAITRite®, CIR Systems) and a concomitant 2D video recording. Patients and healthy subjects underwent a standardized gait protocol with eight different gait conditions: walking in preferred speed (PS), slow speed (SS), and maximum walking speed (MS); walking during head reclination (HR) and eyes closed (EC); walking during cognitive calculatory dual task (serial 7 subtractions; DTC), semantic dual task (verbal fluency; DTS), and motoric dual task (carrying a tray; DTM). For each condition, spatiotemporal gait parameters were calculated and analyzed. Parameters are summarized in five independent gait domains, which are based on a previous study^{21 (link)}: (1) Pace: velocity (m/s), stride length (m), stride time (s). (2) Cycle: swing phase (%), double support phase (%). (3) Variability: stride length coefficient of variation (CV) (%), stride time CV (%), swing phase CV (%). (4) Asymmetry: stride length asymmetry (%), stride time asymmetry (%), swing phase asymmetry (%). (5) Support: stride width (m), stride width CV (%). Occurrences of “stops walking while talking” and freezing of gait phenomena were identified by two independent investigators (KM and RS) based on video recordings.

As detailed previously, testing occurred on a 5.8-m-long pressurized walkway (GAITRite, CIR Systems Inc., Clifton, NJ) centered within a 12.1-m laboratory space, and participants began and ended each walking trial at least one stride before and after the walkway^{7 (link)}. The same research assistant provided 24 different prompts used to elicit a range of walking speeds, participants walked 3 times per prompt, and the order of prompts were randomized across participants (for the list of prompts used, see Brinkerhoff et al.^{7 (link)}). The prompt was repeated prior to each walking trial. Therefore, we collected and analyzed kinematic data during 72 walking trials per participant.