Real and perceived feet orientation under fatiguing and non-fatiguing conditions in an immersive virtual reality environment

Lower limbs position sense is a complex yet poorly understood mechanism, influenced by many factors. Hence, we investigated the position sense of lower limbs through feet orientation with the use of Immersive Virtual Reality (IVR). Participants had to indicate how they perceived the real orientation of their feet by orientating a virtual representation of the feet that was shown in an IVR scenario. We calculated the angle between the two virtual feet (α-VR) after a high-knee step-in-place task. Simultaneously, we recorded the real angle between the two feet (α-R) (T1). Hence, we assessed whether the acute fatigue impacted the position sense. The same procedure was repeated after inducing muscle fatigue (T2) and after 10 min from T2 (T3). Finally, we also recorded the time needed to confirm the perceived position before and after the acute fatigue protocol. Thirty healthy adults (27.5 ± 3.8: 57% women, 43% men) were immersed in an IVR scenario with a representation of two feet. We found a mean difference between α-VR and α-R of 20.89° [95% CI: 14.67°, 27.10°] in T1, 16.76° [9.57°, 23.94°] in T2, and 16.34° [10.00°, 22.68°] in T3. Participants spent 12.59, 17.50 and 17.95 s confirming the perceived position of their feet at T1, T2, T3, respectively. Participants indicated their feet as forwarding parallel though divergent, showing a mismatch in the perceived position of feet. Fatigue seemed not to have an impact on position sense but delayed the time to accomplish this task.