Thermodynamics of Animal Locomotion

Area of Science:

• Biomechanics
• Thermodynamics
• Animal Locomotion

Background:

• Classic muscle models treat muscles as isolated biomechanical entities, neglecting physiological and environmental factors.
• Living organisms face constraints that influence muscle action during locomotion.
• A thermodynamic perspective offers a new framework for understanding muscle function in vivo.

Purpose of the Study:

• To elucidate the overarching principle of living muscle action for locomotion from a thermodynamic viewpoint.
• To introduce and apply the concept of energy cost of effort.
• To analyze energy management and optimization in horses across different gaits.

Main Methods:

• Modeling muscles as an assembly of parallel actuators undergoing chemical-to-mechanical energy conversion.
• Utilizing a compact, locally linear nonequilibrium thermodynamics model.
• Analyzing experimental data on oxygen consumption in horses at three gaits.

Main Results:

• Horses mobilize a consistent number of muscle units for a given gait to minimize waste per distance.
• The number of active muscle units changes significantly during transitions between gaits.
• Locomotor mechanical function is influenced by the animal's thermodynamic properties and the metabolic operating point.

Conclusions:

• Muscle action in locomotion is best understood through a thermodynamic lens, considering energy conversion and efficiency.
• The energy cost of effort is a key parameter generalizing oxygen cost of transport.
• Horses exhibit distinct muscle unit recruitment strategies for different gaits, optimizing energy expenditure.