Exploring associations of perceived mental fatigue and perceived energy with gait characteristics during level and downhill walking in healthy young adults

Abstract

Mental fatigue may influence locomotor control, but evidence in healthy young adults is limited. This study examined whether a 40-minute working-memory task was accompanied by changes in perceived fatigue and cognitive performance and whether subjective fatigue and energy states were associated with pre-to-post changes in gait during level and downhill treadmill walking. Forty healthy young adults were included in the analyses and randomly assigned to a low-load 0-back condition ( n  = 21) or a high-load 2-back condition ( n  = 19); questionnaire-based analyses used the 38 participants with complete data. We assessed mental and physical energy and fatigue immediately before and after the task using the Mental and Physical State and Trait Energy and Fatigue Scales. We recorded reaction time and accuracy across five task blocks. Gait was assessed with six inertial sensors before and after the task during level walking (0°) and downhill walking (9° decline) at 5 km/h. Associations between subjective fatigue and energy ratings and pre-to-post changes in gait parameters were examined using Pearson correlations. Perceived mental fatigue increased and perceived mental energy decreased after the cognitive task. Perceived physical fatigue also increased, whereas perceived physical energy did not change significantly. Reaction times improved across blocks in both conditions; accuracy decreased in the 0-back condition and increased in the 2-back condition. The divergent subjective and behavioral responses indicate increased perceived mental fatigue without convincing evidence of cognitive performance fatigability. Most exploratory fatigue-gait correlations did not reach nominal significance. During downhill walking, perceived mental fatigue showed a small-to-moderate exploratory association with elevation at midswing ( r  = 0.329, unadjusted p  = 0.044). Exploratory associations were also observed between trunk coronal range of motion and subjective physical energy, physical fatigue, and mental energy during downhill walking, and between trunk coronal range of motion and mental energy during level walking. These correlations indicate covariation between subjective states and lateral trunk movement but do not provide evidence of impaired stability. No association remained significant after false-discovery-rate correction across all 200 correlations. In healthy young adults, perceived fatigue and energy states showed selective exploratory associations with changes in trunk and foot movement rather than widespread associations with gait parameters. The associations involving trunk coronal range of motion may reflect an altered movement strategy or normal movement variability; without direct measures of dynamic stability, their functional relevance cannot be determined. Similarly, the association with elevation at midswing raises the hypothesis that perceived mental fatigue may relate to a more cautious foot-trajectory strategy. This hypothesis could not be tested with the present measurements and requires confirmation with direct biomechanical and stability measures; the finding does not establish a safer or compensatory gait adaptation. Larger, preregistered studies with correction for multiple comparisons and direct biomechanical and stability measures are needed.