Foot anatomy specialization for postural sensation and control.

Area of Science:

• Biomechanics
• Anthropology
• Human Physiology

Background:

• Anthropological and biomechanical research highlights the human foot's unique evolutionary design for propulsion and support.
• Traditional postural studies often overlook the foot's arch and toes, focusing instead on ankle joint function.
• The precise role of foot anatomy and sensorimotor control in maintaining posture requires further investigation.

Purpose of the Study:

• To quantify foot arch deformation under load.
• To investigate the impact of localized perturbations on the toes (TOE) or metatarsals (MT) on posture during standing.
• To explore the foot's contribution to bipedal postural control.

Main Methods:

• Quantified foot arch deformation using an arch probe while applying loads.
• Measured electromyogram (EMG) activity of the tibialis anterior and gastrocnemius muscles during perturbations.
• Analyzed shin sway variability (root-mean-square - RMS) in response to toe and metatarsal perturbations.
• Recorded changes in foot arch height during load application and removal in a sitting position.

Main Results:

• Foot arch height changed by 1-1.5 mm with knee loading/unloading, with skin compression accounting for less than 50% of this.
• A significant correlation was observed between foot arch flattening and forward tibial tilt during quiet standing.
• Perturbations to the toes (TOE) and metatarsals (MT) caused significant changes in muscle activity (EMG) and increased shin sway (RMS) variability.
• The MT condition resulted in greater RMS variability increases compared to the TOE condition.
• Recovery of RMS to baseline levels after perturbations took over 30 seconds, suggesting a recalibration of the sensorimotor system.

Conclusions:

• The human foot is not a rigid support but a compliant, active structure highly sensitive to minor deformations.
• Foot architecture and physiology play a crucial role in the fine-tuned control of bipedal posture.
• Minute foot perturbations can significantly alter postural control mechanisms, requiring substantial sensorimotor adaptation.