Training procedures
cognitive and motor dual tasks
SAID
The first training session on the CAREN started with a familiarization procedure, where the participant could get used to the system by walking on the treadmill in the virtual environment. Participants reported a numeric rating scale (NRS) score for how comfortable they felt when walking on the CAREN before and during familiarization (0; very uncomfortable to 10; fully comfortable). If a score of 7 or higher was reached, the familiarization procedure was deemed complete. This was expected to occur within 6–7 min [After this, each participants’ comfortable walking speed was determined using a ramp protocol. Subjects started walking at 0.5 m/s and speed was gradually increased until the subject said ‘stop’ when their comfortable walking speed was reached. The participant then walked unperturbed at this speed for approximately one minute to check if any adjustments needed to be made. Due to the procedures for familiarization and determining the comfortable walking speed, the total duration of the first training session could be up to 40 min.Consecutive sessions started with a warm-up during which the participant walked unperturbed on the treadmill at their comfortable speed (determined during the first session) for approximately 3 min and got readjusted to the system. Each training session consisted of three parts: gait adaptability, static and dynamic reactive balance control (of which details are given below). During training, participants were regularly asked to rate how challenging it was to maintain their balance on an NRS score (0–10; 0 = not challenging at all, 10 = unable to maintain balance). To ensure that the training was challenging but acceptable and tolerable for each participant, the aim was to train at a difficulty level between 6 and 9 (challenging to very challenging) on the NRS. Training progression was based on these NRS scores, and each participant’s ability to manage the perturbations. Training difficulty was progressed by increasing the perturbation intensity and walking speed. During the second and final training sessions, cognitive and motor dual tasks (e.g., counting backwards in steps of 7, hitting targets in the virtual environment) could also be added to increase training difficulty. Participants were aware that there would be ‘various challenges to their balance’ during the training, and were instructed to recover their balance and to try to continue walking. Participants were naïve to the timing and the order of perturbation types that would be applied. Training adherence (number of training sessions attended and completed, reasons for missed training sessions) was monitored throughout the study, and participants were encouraged to reschedule any missed training sessions.