Feeling Mentally Drained May Nudge How Young Adults Walk Downhill, Exploratory Study Finds

A demanding stretch of mental work can leave healthy young adults feeling distinctly tired — but their walking barely changes. That is the nuanced takeaway of a new exploratory study from the University of Stuttgart, published in Frontiers in Sports and Active Living, which set out to determine whether subjective feelings of mental fatigue and energy are mirrored in measurable changes in gait during level and downhill treadmill walking.

The research team, Thomas Jürgen Klotzbier and Nadja Schott of the Department of Sport and Exercise Science, recruited 40 healthy young adults with an average age of 22.4 years. Participants were randomly assigned to one of two versions of a working-memory task known as the n-back task. In the low-load 0-back condition, 21 participants simply pressed one key when the letter “a” appeared on screen and another key for the letters “b,” “c,” or “d.” In the high-load 2-back condition, 19 participants had to judge whether each letter matched the one shown two trials earlier — a manipulation that substantially increases working-memory demands. Each session involved five blocks of 160 trials over roughly 40 minutes, with brief breaks in between.

Before and immediately after the cognitive task, participants rated their current state using the Mental and Physical State and Trait Energy and Fatigue Scales, in which each subscale combines three visual-analogue items scored from 0 to 420 millimetres. The ratings told a clear story. Perceived mental fatigue rose significantly, with a mean increase of 74.4 points, and perceived mental energy fell by 61 points, both highly significant in the repeated-measures analysis. Perceived physical fatigue also increased by a smaller but significant margin of 43.3 points, whereas the decline in physical energy — 22.2 points on average — did not reach statistical significance. Notably, the magnitude of these changes did not differ significantly between the 0-back and 2-back groups, suggesting that even a repetitive, lower-load task performed for 40 minutes was enough to shift subjective state.

Here, however, came the first of the study’s important dissociations. Although participants felt considerably more fatigued, their objective performance on the task did not deteriorate in a consistent way. Reaction times actually improved across the five task blocks in both conditions. Accuracy decreased in the 0-back condition but improved in the 2-back condition. The authors therefore describe the results as evidence of increased perceived mental fatigue rather than convincing cognitive performance fatigability — a distinction they emphasize, since subjective tiredness and objective decline in performance are related but separate phenomena. Practice, familiarization, or strategy adaptation may have offset any fatiguing effect of the task.

The second half of the study asked whether these subjective states were reflected in the body’s movement. Each participant walked on a treadmill at a fixed speed of 5 km/h under two conditions — level walking at 0 degrees and downhill walking at a 9-degree decline — once before and once after the cognitive task. Gait was captured with six APDM Opal inertial sensors attached to the wrists, ankles, lower back, and sternum, sampling at 128 Hz, with the Mobility Lab system detecting foot contact and toe-off events and computing a broad battery of spatio-temporal parameters, from stride length and cadence to trunk range of motion and foot elevation during the swing phase. On average, about 29 steps per 40-second trial entered the analysis.

The headline result is, in a sense, an absence of results. Of the 200 correlations computed between post-task fatigue and energy ratings and pre-to-post changes in gait parameters, only five reached unadjusted significance — fewer than the roughly ten that would be expected by chance alone. And after Benjamini–Hochberg false-discovery-rate or Holm correction across all 200 tests, none of the associations remained statistically significant; the smallest adjusted p-value was 0.80. The authors are careful to stress that these findings are exploratory and hypothesis-generating, not confirmatory evidence.

Still, the few nominal associations are intriguing enough to shape future research. During downhill walking, perceived mental fatigue showed a small-to-moderate positive association with elevation at midswing — the height to which the foot is raised during the middle of the swing phase — with r = 0.329, a 95% confidence interval of 0.010 to 0.587, and an unadjusted p-value of 0.044. The researchers speculate that this could reflect a more cautious foot-trajectory strategy: when walking downhill, which demands continuous braking and control of forward progression, keeping the foot higher might increase clearance from the walking surface. But they are emphatic that this hypothesis could not be tested with the present measurements. Elevation at midswing is not the same as minimum toe clearance, no direct stability or trip-response measures were taken, and the finding does not establish a safer or compensatory gait adaptation.

The other cluster of nominal findings concerned trunk coronal range of motion — lateral trunk movement in the frontal plane, which helps regulate the body’s center of mass relative to its base of support. During downhill walking, subjective physical energy (r = −0.452), mental energy (r = −0.401), and physical fatigue (r = 0.344) were each nominally associated with changes in this parameter, and mental energy also showed a nominal association during level walking (r = −0.345). In other words, participants who felt more fatigued or less energetic tended to show greater lateral trunk movement after the task. The authors caution that this pattern may reflect an altered movement strategy or simply normal movement variability rather than impaired stability. They point to prior work showing that trunk motion, step width, and center-of-mass control are functionally coupled, and to the idea that movement variability can be functional when it allows performance to be maintained under changing constraints. Crucially, the correlational design cannot show that fatigue caused the changes, and no direct measures of dynamic stability were obtained.

The study carries a detailed list of limitations that the authors themselves lay out candidly. The sample of 38 complete cases for the questionnaire analyses provided 80% statistical power only for correlations of approximately |r| = 0.44 or larger, so smaller associations could easily have been missed — and the absence of significant correlations should not be read as proof that gait was entirely unaffected. The 0-back condition cannot be considered a fatigue-free control, since 40 minutes of even repetitive responding may induce boredom, reduced arousal, or fatigue. Gait change scores were based on a single 40-second recorded trial per condition and time point, leaving them vulnerable to measurement error and regression to the mean. The fixed treadmill speed may have imposed different relative demands on different participants, and the fixed order of the walking conditions means that level-versus-downhill contrasts may partly reflect order effects. No recovery period was scheduled, the exact intervals between task and post-task walking were not recorded, and variables such as sex, body mass index, and physical activity were not controlled in the correlation analyses. Finally, because the 2-back group reported more weekly physical activity on average (295 versus 226 minutes), baseline equivalence between conditions was not established.

What emerges, then, is a picture of selectivity rather than widespread impairment: in healthy young adults, subjective fatigue and energy states showed scattered, exploratory associations with trunk and foot movement but no broad pattern of fatigue-related gait change. The authors call for larger, preregistered, adequately powered studies with prespecified primary outcomes, correction for multiple comparisons, direct measures of dynamic stability such as minimum toe clearance and mediolateral margin of stability, joint kinematics, and muscle activity, as well as randomized or counterbalanced comparisons of level, uphill, and downhill walking and comparisons across age groups. Until such work is done, the findings stand as a careful first step — evidence that a mental workout can make young adults feel drained without detectably disrupting the mechanics of how they walk, but with tantalizing hints that the most demanding terrain may subtly reshape the foot’s path.

Subject of Research: Associations between perceived mental fatigue and energy and gait characteristics during level and downhill walking in healthy young adults

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

Article References: Klotzbier, T. J., & Schott, N. (2026). Exploring associations of perceived mental fatigue and perceived energy with gait characteristics during level and downhill walking in healthy young adults. Frontiers in Sports and Active Living, 8, Article 1973398. https://doi.org/10.3389/fspor.2026.1973398

Image Credits: AI Generated

DOI: 10.3389/fspor.2026.1973398

Keywords: mental fatigue, gait analysis, downhill walking, working memory, n-back task, inertial sensors, trunk range of motion, midswing elevation, young adults, biomechanics, treadmill walking, exploratory study