Lower extremity fatigue increases complexity of postural control during a single-legged stance

Area of Science:

• Biomechanics
• Non-linear dynamical systems
• Human movement analysis

Background:

• Non-linear methods offer complementary insights to linear approaches in assessing postural control.
• Control Entropy (CE) quantifies complexity in non-stationary signals, previously shown to decrease with exhaustive exercise in running.
• This study investigates if CE can detect changes in postural control complexity following fatiguing exercise.

Purpose of the Study:

• To determine if the complexity of postural control decreases following fatiguing exercise using Control Entropy (CE).

Main Methods:

• Ten healthy subjects performed single-legged balance tests before and after a fatiguing Wingate anaerobic test (WAnT) or a rest period.
• High-resolution accelerometers recorded center of mass (COM) accelerations in three axes (VT, ML, AP) at 625 Hz.
• Control Entropy (CE) analysis and a novel R-test statistic were applied to assess signal complexity.

Main Results:

• Fatiguing exercise significantly increased overall CE in the vertical (VT) and medial/lateral (ML) axes compared to pre-fatigue and rest conditions.
• Post-fatigue CE was also higher in the anterior/posterior (AP) axis compared to the rest condition.
• Fatigue eliminated the differential complexity response between axes observed in non-fatigued states.

Conclusions:

• Fatiguing exercise increases postural control complexity across all axes.
• Fatigue eliminates the distinct complexity patterns typically observed between different axes of movement.
• These findings highlight the impact of fatigue on the control system's strategies for maintaining postural stability.