Visual Contributions to Balance Control During Gait Kyle Brozek1, Mukul Mukherjee1 1Department of Biomechanics, University of Nebraska at Omaha, Omaha, NE, USA BACKGROUND METHODS Balance control during gait is affected by the orthogonality of movement1,2. It has been shown that the direction of optic flow (OF) influences balance control during gait3,4. When walking in the forward direction, a person relies on the central nervous system for balance in the side-to-side or mediolateral (ML) direction. When walking in the forward direction, a person relies on passive actions related to spinal reflexes and mechanical constraints for balance in the anteroposterior (AP) direction5. Walking in the ML direction causes a person to reverse control such that balance control patterns in the AP direction (direction of progression) indicate active control while passive actions for balance are observed in the ML direction (direction orthogonal to progression). Virtual reality environments can increase gait instability in healthy subjects6 Figure 1: Baseline trial setup Figure 2: Incongruent VR-Gait setup METHODS 20 healthy adults (19 to 35 years), who do not have any lower limb dysfunction, cognitive impairments, cardiovascular or other abnormalities that could affect walking will be recruited. The protocol will be conducted on the Computer Assisted Rehabilitation ENvironment (CAREN) in the Gait laboratory in the Department of Biomechancis. The CAREN consists of a split-belt, instrumented treadmill suspended on a six-degree-of-freedom motion-based platform. It is outfitted with 12 motion capture cameras which allow the collection of kinematic locomotion data at 100Hz. 57 markers at specific anatomical landmarks (foot, pelvis, and trunk), will be placed on participants to allow collection of data. The experimental protocol (table 1) will consist of five 5-minute walking trials at a self-selected preferred walking speed (PWS). The first trial will be to familiarize with the setup. All trials will be performed in an immersive VR environment where a virtual path will be displayed on a screen in front of the treadmill. After the first five-minute baseline trial in which the VR and the support surface will not be oscillating, the following 4 trials will comprise of a random order of trials with either VR environment or treadmill oscillations or both (congruent or incongruent). When both treadmill and VR are oscillating (trials 4 and 5), participants will walk at a PWS while the platform and the virtual path both oscillate in the same (trial 4) and opposing (trial 5) directions. Figure 3: Congruent VR-Gait setup Figure 4: Incongruent VR-Gait setup DISCUSSION We expect that the results of this study will allow us to determine the contribution of visual feedback on the orthogonal relationship between gait and balance control during treadmill walking. We hypothesize (Figure 5) that the orthogonal relationship between gait and balance control will reverse during normal treadmill walking if visual feedback is reversed (congruent to incongruent). Additionally, the orthogonal relationship between gait and balance control will demonstrate a strong linear relationship with OF direction during normal treadmill walking. Figure 5: Congruent vs. Incongruent optic flow during AP and ML walking (preliminary data) REFERENCES Table 1: Experimental protocol for walking trials Condition 1. Baseline 2. Incongruent VR 3. Incongruent Gait 4. Congruent VR-Gait 5. Incongruent Treadmill state Non-oscillating Oscillating* VR state Wurdeman SR, et al. J of Biomechanics, 45(4), 653-659, 2012. Bauby CE, et al. J of Biomechanics, 33(11), 1433-40, 2000. 3. Warren WH, et al. J Exp Psychol Hum Percept Perfom. 4, 818-838, 1996. 4. Logan D, et al. Experimental Brain Research, 206(3), 337-350, 2010. 5. Kuo AD, et al. Robotics Research, 18(9), 917-930 (1999). 6. Hollman JH, et al. Gait and Posture. 23, 441-444 (2005). * Between +19o and -19o