This randomized crossover study investigates the effects of mental fatigue on postural control and spinal reflex excitability in healthy physically active adults aged 18-35 years. Participants will complete two experimental conditions: a mentally fatiguing Stroop task and a control condition involving passive documentary watching, separated by at least 48 hours. Postural control will be assessed using force plate measures of center of pressure displacement during bipedal and unipedal stance, with and without concurrent cognitive dual-tasking. In parallel, spinal reflex excitability will be evaluated using H-reflex recordings from the triceps surae muscles across sitting and standing postures. The primary aim is to determine whether mental fatigue increases postural sway, particularly in more challenging balance conditions such as single-leg stance. The secondary aim is to examine whether mental fatigue alters the normal modulation of spinal reflex excitability across progressively demanding postural tasks. Additional biomechanical and neuromuscular measures, including EMG activity and hip kinematics, will be recorded to provide insight into underlying control mechanisms. The study will include approximately 26 participants, with each serving as their own control. Data will contribute to understanding how cognitive fatigue influences balance control and spinal-level neuromuscular regulation.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
BASIC_SCIENCE
Masking
SINGLE
Enrollment
26
Participants complete a 60-minute computerized Stroop color-word task designed to induce mental fatigue. The task consists of repeated incongruent stimuli requiring rapid and accurate responses, with difficulty individualized based on a prior maximal Stroop performance test. Performance (reaction time and accuracy) is continuously recorded. Subjective mental fatigue is assessed intermittently during the task using a visual analogue scale.
Participants watch a 60-minute neutral documentary of their choice. This condition is designed to match the mental fatigue intervention in duration and general sensory engagement without inducing cognitive fatigue. No cognitive task performance is required. Subjective mental fatigue is assessed at equivalent time points using a visual analogue scale.
Vrije Universiteit Brussel
Brussels, Pleinlaan 2, Belgium
Center of Pressure (CoP) Displacement (Postural Sway)
Postural sway will be assessed using center of pressure (CoP) displacement area and oscillation parameters measured during bipedal and unipedal stance on a force plate. Higher values indicate greater postural instability. Comparisons will be made between mental fatigue and control conditions, pre- and post-intervention.
Time frame: Pre-intervention and immediately post-intervention (each experimental session)
Subjective Mental Fatigue
Subjective mental fatigue will be assessed using a visual analog scale (VAS) ranging from 0 (no fatigue) to 100 (extreme fatigue).
Time frame: During intervention (every 15 minutes) and immediately post-intervention
Spinal Reflex Excitability (H-reflex Modulation)
Spinal reflex excitability will be assessed using H-reflex amplitude (H50 and Hmax), normalized to maximal M-wave (Mmax), recorded from the triceps surae muscles (soleus, medial gastrocnemius, lateral gastrocnemius) during sitting, bipedal stance, and unipedal stance. Changes will be compared between mental fatigue and control conditions.
Time frame: Pre-intervention and immediately post-intervention across sitting, bipedal stance, and unipedal stance conditions
Surface Electromyography (EMG) Activity of Postural Muscles
Muscle activation will be assessed using root mean square (RMS) electromyography (EMG) activity recorded from the soleus, medial gastrocnemius, lateral gastrocnemius, tibialis anterior, vastus medialis, and multifidus muscles, normalized to maximal M-wave (MMAX).
Time frame: Continuous recording during postural tasks, pre-intervention and immediately post-intervention (each condition)
Hip / Leg Movement (IMU Angular Velocity)
Hip and leg movements will be assessed using inertial measurement unit (IMU) sensors placed at the proximal femoral epicondyle. Outcome is the resultant angular velocity across movement axes during postural tasks.
Time frame: Pre-intervention and immediately post-intervention during bipedal and unipedal stance
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