# Effects of Acute Exposure to Virtually Generated Slip Hazards during Overground Walking
## 2 Materials and Methods
### Experimental Procedures  
Data collection consisted of a total of two days: one familiarization day and one testing day. Following initial familiarization during day one, each participant's age, height, mass, and shoe size were recorded. Participants were then provided a pair of slip-resistant work shoes to be worn during baseline balance testing and during the practice gait trials. The same shoes would be worn during day two of data collection. Several Timed Up-and-Go (TUG) tests were then completed, which previous literature explains are a predictor of one's ability to maneuver an environment with relative safety [36]. These included a standard TUG (TUG-S), cognitive TUG (TUG-C), and a manual TUG (TUG-M). The standard TUG involved the participant sitting in a chair, then, on command, walking 3 m, turning around, walking back to the chair, and sitting down. Similar to the TUG-S, TUG-C involved the same task but included counting backward from 100 by a number that was randomly assigned prior to each trial. Finally, participants completed TUG-M, which is similar to the standard TUG, with a standard anterior load of 15 lb. assigned to all participants to be carried throughout the test. Additionally, because the participants would be exposed to VR during data collection, all participants were exposed to the virtual environment and given the opportunity to perform several gait trials across a walkway located in the center of the lab, both in the REAL and VR environments. However, during familiarization, no practice trials in which the participants were exposed to the slip hazards were administered in order to avoid a learning effect [37]. Completion of the practice gait trials marked the end of day one of testing.  
Figure 1: Side-by-side comparison of REAL (**left**) and VR (**right**) environments. Lower extremity joint kinematics were recorded when the participant walked across the gray walkway in the center of the lab.  
Less than a week later, upon arrival for day two of data collection, participants were given tight-fitting athletic clothes and the slip-resistant work shoes they wore during baseline testing. Reflective motion capture markers were then attached bilaterally using a lower-body Helen-Hayes model provided in Motion Analysis Cortex. After preparation, the participants were directed to the walkway and placed in the fall arrest system to prevent fall-related injuries during testing. During the REAL condition, participants were asked to walk at a self-selected pace across the dry walkway with no slip hazard present while their lower body joint kinematics were recorded during a normal gait (NG) trial as a baseline measurement. Following the NG trial, the slip hazard was placed in the middle of the walkway without any warning (unexpected slip: US), followed by an additional slip perturbation trial with a warning (expected slip: ES). NG was recorded for each participant before exposure to the slip hazard, making a total of 3 trials recorded: NG, US, and ES.  
Following these trials (NG, US, ES) in the REAL condition, all 3 TUG variations were performed again followed by a 10-minute rest period given to the participants to reduce the potential for the development of fatigue. Participants then donned the HTC Vive VR headset to perform the same trials in a similar manner. Therefore, gait trials were performed in the VR condition in the following order: NG, US, and ES. Immediately following exposure to the VR environment, participants then completed a post-intervention SSQ to assess the effects of the VR environment on the participant. Participants then completed another series of TUG-S, TUG-C, and TUG-M. Completion of all the TUG variations marked the end of data collection. All participants were exposed to both environmental conditions during testing. The order of exposure to environmental conditions (REAL and VR) was assigned in a counterbalanced order.