The goal of this study is to comprehend how mental fatigue could affect human gait. The main questions to answer are:

• Does mental fatigue change how people walk?
• How long does it take for walking patterns to return to normal after mental fatigue sets in?
• What role do constructs like boredom, sleepiness, and motivation play in this relationship?

To achieve this, participants will take part in the experiment, split into two sessions:

Day 1 (online, about 25 minutes): Practice session. Participants will practice a computer task that will be used to induce mental fatigue in the next session.

Day 2 (in-person, about 1.5 to 2 hours): Participants will wear several wearable sensors: motion sensors on their legs, feet, and back, sensor insoles in their shoes, a cap that measures brain activity, and glasses that track eye movement. After sensor placement, participants will walk in a straight line for 10 meters to measure their normal walking pattern. They will then complete a 32-minute computer task designed to induce mental fatigue. Afterward, participants will walk in a straight line for 10 meters again, rest for 3 minutes, and repeat this walk-and-rest cycle 3 more times. Participants will also answer short questions about how tired, bored, and alert they feel throughout the session.

Background:

Most prior research on mental fatigue and gait has examined concurrent dual-task walking, in which a cognitive task and walking occur simultaneously. It remains unclear whether gait is altered following (rather than during) a mentally fatiguing task. This study addresses that gap using TloadDback, an adaptive N-back paradigm (Borragán et al., 2016) that individually calibrates cognitive demand to maintain consistent task difficulty across participants, as the mental fatigue induction method.

Design:

This is a within-subject, repeated-measures design. All primary analyses will be conducted on data collected during the in-person session. Sample size (up to 30 enrolled, target N = 24) was determined via a power analysis using pilot data (N = 5; within-subject design, α = 0.05, power = 0.90).

Mental Fatigue Induction Task:

TloadDback is administered as a single continuous 32-minute block. Participants view a continuous sequence of number-letter-number stimuli and respond via keypress (odd/even number), when seeing a number, or spacebar (letter repeat), when seeing a letter. Stimulus-presentation speed is individually calibrated during the practice session to the maximum speed at which the participant maintains greater than 85% accuracy, ensuring standardized cognitive demand across participants during the main session.

Sensor:

Inertial measurement units (IMUs): 8 units, placed at the shanks (2), thighs (2), feet (2), upper spine (1), and lower back (1), capturing spatiotemporal and kinematic gait parameters.

Pressure-sensing insoles: worn inside participants' shoes to detect gait events (heel strike, toe-off), complementing IMU-derived timing data.

Eye tracker: recording pupil diameter, blink rate, and fixation duration.

EEG cap: records brain's electrical voltage fluctuaction to obtain metrics such as frequency band analysis and neural signals related.

IMUs and insoles are used primarily to obtain gait parameters, whereas eye tracking and EEG are used only during the mental fatigue-inducing computer task, serving as physiological metrics to corroborate fatigue.

Procedures

Practice session (remote, online via PsychoPy/Pavlovia): Participants complete a familiarization run of TloadDback for individual speed calibration

In-person session pipeline:

Demographic questionnaire. Sensor placement: IMUs and insoles Baseline gait trial (10-meter straight-line walk). A 3-minute Psychomotor Vigilance Task (PVT), in which participants respond as quickly as possible by pressing the spacebar each time a visual stimulus (a dot) appears at random inter-stimulus intervals.

Sensor placement: Eye tracker and EEG. TloadDback task (32 minutes continuous). Repeat the 3-minute Psychomotor Vigilance Task (PVT). Take off the Eye Tracker and EEG. Post-task gait and recovery assessment: repeated cycles of a straight-line walk trial followed by a 3-minute rest, for a total of 4 post-task walk assessments.

Visual Analog Scale (VAS) ratings (fatigue, boredom) are collected at multiple points across the session to track the time course of fatigue and alertness.

Inclusion Criteria:

• Adults aged 18-60 years.
• Neurotypical individuals with no self-reported history of neurological or cognitive disorders.
• Able to walk independently, without an assistive device.
• Fluent in English.
• Recruitment will aim for gender balance across the sample.
• For Day 2, participants must arrive with clean, dry hair, free of styling products (e.g., gels, oils), to ensure adequate EEG electrode contact.

Exclusion Criteria:

• Outside the age range of 18-60 years.
• Self-reported history of neurological or cognitive disorders (e.g., epilepsy, multiple sclerosis, stroke/traumatic brain injury).
• Any musculoskeletal condition or injury affecting normal gait.
• Use of an assistive device for walking (e.g., cane, walker, brace).
• Self-reported photosensitive epilepsy or seizure disorder triggered by screen/visual stimuli.
• Non-English speaking.
• Day 2 restrictions: less than 6 hours of sleep the night before; caffeine within 2 hours of the session; alcohol within 24 hours of the session.

A decision on data sharing has not yet been finalized. I intend to complete the IRB review process first, incorporating any feedback or requirements related to data collection, de-identification, and storage. Once IRB approval is obtained, a formal individual participant data (IPD) sharing plan will be developed, taking into account any applicable restrictions on data publication and participant privacy protections.