Age-related differences in the effect of mental fatigue on obstacle crossing in virtual reality

Wasaki, Natsuko; HIRANAI, Kazuki; Takahashi, Akiko · 2025 · OpenAlex-citations

DOI: 10.1038/s41598-025-94038-6

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Summary

This study investigates how mental fatigue interacts with aging to influence physical performance, specifically obstacle crossing, a key factor in occupational fall risks. Motivated by the high prevalence of falls among workers in Japan, particularly those attributed to inattention, the research aimed to compare the effects of mental fatigue on younger adults (aged 25–34) and middle-aged adults (aged 55–64). While both aging and mental fatigue independently impair cognitive and motor functions, their combined impact on physical movements had not been fully understood. The study sought to identify age-specific fall risks exacerbated by mental fatigue to inform preventive strategies for older workers. The experimental design involved 34 participants who performed an obstacle-crossing task in a virtual reality (VR) environment before and after a 30-minute mental workload task (the Uchida–Kraepelin test) designed to induce mental fatigue. Fatigue was assessed subjectively using a Visual Analog Scale (VAS) and objectively via the Psychomotor Vigilance Task (PVT). The VR task measured foot clearance (distance above obstacles) and swing time (duration of passing over obstacles) for both leading and trailing feet across obstacles of varying heights. Motion tracking devices attached to the participants' feet recorded these kinematic parameters. Statistical analyses included repeated-measures ANOVA to examine the main effects of age and mental fatigue, as well as their interaction. Results indicated that mental fatigue significantly increased subjective fatigue levels in both groups, with younger adults reporting higher fatigue than middle-aged adults. However, mental fatigue did not significantly affect PVT reaction times or lapses, though middle-aged adults generally exhibited slower reaction times and more lapses regardless of fatigue status. Crucially, mental fatigue significantly reduced foot clearance for both the leading and trailing feet in both age groups. Middle-aged adults maintained greater trailing foot clearance than younger adults, likely as a compensatory safety strategy. However, middle-aged adults showed a tendency toward faster swing times for the leading foot, suggesting reduced balance control. The study found that while mental fatigue impaired physical performance similarly across ages, the underlying risk factors differed: younger adults adopted energy-efficient strategies that increased fall risk, whereas middle-aged adults faced heightened risk due to reduced balance control and lower sensitivity to their own fatigue levels. The findings highlight that mental fatigue increases fall risk across all ages but through distinct mechanisms. For middle-aged adults, the combination of reduced balance control and diminished awareness of fatigue creates a unique vulnerability, potentially leading to falls even when they maintain safety margins in other aspects of movement. The study underscores the importance of early guidance and education before middle age to mitigate these risks. It suggests that interventions should address not only the physical effects of fatigue but also the cognitive and motivational changes that alter movement strategies differently depending on age. These insights are critical for developing targeted occupational safety measures in aging societies.

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