Mental fatigue (MF) negatively affects both cognitive and physical performance, increasing the risk of errors in high-stakes environments such as sports and surgery. Traditional methods to assess MF rely on subjective self-report scales, which are prone to bias, or on complex brain measurements (e.g. EEG) that are impractical outside laboratory settings. This study aims to develop a real-time, objective monitoring method for MF using wearable physiological sensors. The study will recruit healthy, trained runners (18-35 years old) who will complete both an MF-inducing cognitive task (Stroop test) and a control condition (watching a documentary) in a randomized, counterbalanced, crossover design. Heart rate variability, respiration rate, and pupil metrics will be continuously recorded using wearable devices. Machine learning models will be used to predict MF-level as well as the effect of MF on physical performance (5-km time trial on a treadmill) using the physiological data as input.
Healthy (no neurological, cardiovascular or musculoskeletal disorders of any kind)
Male or female
No prior knowledge of the concept of MF
No medication
Injuries in the past 6 months, affecting running performance
Suffering from a chronic health condition (could be neurological, cardiovascular, internal or musculoskeletal)
Participating in any concomitant care or research trials
History of suffering from any mental/psychiatric disorders
Crossover
Mental Fatigue
BehavioralMental fatigue (MF) is a psychobiological state characterized by feelings of tiredness and/or a measurable decline in performance following prolonged or intense cognitive activity.
Heart rate variability time-domain parameters
Root mean square of successive differences \[RMSSD\], standard deviation of normal-to-normal intervals \[SDNN\] in milliseconds.
Heart rate variability frequency-domain parameters
Low-frequency (LF), High-frequency (HF) in milliseconds squared (ms²) and Low/high-frequency ratio \[LF/HF\]
Respiration rate
Respiration rate (RR) will be measured as the number of breaths per minute (breaths/min)
Pupil diameter
Pupil diameter (PD) will be measured in millimeters (mm) as an index of autonomic nervous system activity.
Subjective feeling of Mental Fatigue
The Mental Fatigue Visual Annalogue Scale (0-10cm) will assess how mentally fatigued the participant is feeling (100 point VAS scale), and ranges from 'not at all' to 'completely exhausted'.
Mood
The Brunel Mood Scale (BRUMS) will be used to indicate mood, and serve as a control measure for both arousal as well as boredom. It features 24 mood descriptors (divided into 6 subscales (i.e. anger, confusion, depression, fatigue, tension and vigor)), where participants have to give a value for every mood on a 5-point Likert scale (i.e. 0=not at all to 4 = extremely) responding to the question: "how do you feel right now?"
Motivation
Moti-VAS: Motivation will be assessed using a VAS. Participants will be asked "How motivated do you feel for the upcoming task", and will be instructed to rate their answer on a 10cm line, with the statements "not at all" and "extremely motivated" at opposite ends of this line.
Sleepiness
The Karolinska Sleepiness Scale (KSS) will be conducted. This 10-point scale measures the subjective level of sleepiness and goes from 1 = 'extremely alert' to 10 = 'extremely sleepy, falls asleep all the time'.
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