What is Stance Phase On Deformable Substrates?

Area of Science:

• Paleontology
• Biomechanics
• Zoology

Background:

• The stance phase of walking involves forces for support and propulsion.
• Deformable substrates yield under load, causing feet to sink.
• Bipedal animals like birds and dinosaurs exhibit subsurface digit looping on yielding substrates.

Purpose of the Study:

• To analyze the relationship between bipedal walking kinematics and subsurface foot motion on deformable substrates.
• To establish a track-based framework for studying walking in extinct taxa.
• To understand how substrate consistency affects foot movement during the stance phase.

Main Methods:

• Biplanar X-ray imaging was used to record 161 stance phases from 81 trials.
• Three Helmeted Guineafowl (Numida meleagris) walked on substrates of varying consistency (solid, dry granular, muds).
• Kinematic data were analyzed to identify gait events and subsurface looping patterns.

Main Results:

• Foot sinking depth varied up to 78% of hip height across substrates.
• Increased substrate hydration shifted foot motion from above to below ground.
• Six conserved gait events were identified, with five sub-phases forming loops on yielding substrates.

Conclusions:

• Subsurface looping patterns are linked to two-footed coordination and weight distribution.
• The definition of 'stance phase' requires re-evaluation for deformable substrates.
• Understanding subsurface gait mechanics is vital for interpreting fossil dinosaur tracks.