AbstractBACKGROUND: Based on posturography parameters during sleep deprivation (SD), a mental fatigue index (MFI) was constructed for healthy male cadets.METHODS: There were 37 young male subjects who volunteered for two successive days of SD. Their posturography balance, profile of mood status (POMS), and heart rate variability (HRV) were measured at four different times (10:00 and 22:00 of day 1, 10:00 and 22:00 of day 2). According to the methods used in our previous research, similar MFIs based on posturography parameters were computed. Then, correlations of MFIs with POMS scores and HRV values were evaluated by linear and nonlinear methods including quadratic, S-curve, growth, and exponential analyses.RESULTS: MFI continued to increase during SD and MFI as the independent variable had quadratic relationships with fluster (R² 0.057), depression (R² 0.067), and anger (R² 0.05) scores of POMS. A linear correlation was found between MFI and the depression score (R² 0.045) and MFI correlated linearly (R² 0.029) and nonlinearly (R² 0.03) with heart rate. Similarly, MFI reflected changes in the time and frequency domain parameters of HRV, with linear (R²range: 0.0290.082) or nonlinear (R²range: 0.0300.082) relationships.DISCUSSION: The increase of MFI was linked with amplification of personal negative moods and an imbalance of autonomic nervous system activity. The findings suggest that MFI might be a potential indicator of mental fatigue and provide a method to prevent driving fatigue and human errors.Cheng S, Yang J, Su M, Sun J, Xiong K, Ma J, Hu W. Postural stability change under sleep deprivation and mental fatigue status. Aerosp Med Hum Perform. 2021; 92(8):627632.