Estimating instantaneous energetic cost during non-steady-state gait

Area of Science:

• Physiology
• Biomedical Engineering
• Systems Biology

Background:

• Traditional methods using respiratory gases estimate metabolic energy use at steady-state.
• Challenges include slow physiological dynamics and breath-to-breath variability, obscuring instantaneous energy demands.
• Existing methods struggle to accurately reflect real-time energetic costs during non-steady-state conditions.

Purpose of the Study:

• To develop a method for estimating instantaneous energetic cost during non-steady-state conditions.
• To model the relationship between instantaneous energy demands and measured respiratory gas exchange.
• To validate this model for assessing metabolic cost during dynamic activities like gait.

Main Methods:

• Imposed controlled changes in energy use (input) and measured breath-by-breath respiratory responses (output).
• Developed a dynamic systems model, specifically a first-order linear differential equation, to map instantaneous to measured energetic cost.
• Validated the model by estimating instantaneous energetic cost during simulated dynamic gait changes and comparing it to imposed energetic cost profiles.

Main Results:

• A first-order linear differential equation accurately approximated transient energetic cost responses during gait.
• The model demonstrated a mean time constant (τ) of 42 ± 12 s and high fit accuracy (R² of 0.94 ± 0.05).
• Estimated instantaneous energetic cost closely corresponded to imposed energetic cost profiles during dynamic gait simulations.

Conclusions:

• The developed dynamic model reliably estimates instantaneous energetic cost from breath-by-breath respiratory measures.
• This methodology offers a novel approach to study the role of energetics in locomotor adaptation and learning.
• The findings advance the assessment of metabolic energy expenditure beyond steady-state limitations.