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Energy Expenditure
Direct Calorimetry Measurement
➤ Measures heat generated by an organism.
Direct Calorimetry Formula
➤ Substrate (Food) Energy = ~60% Liberated as Heat + ~40%
Conserved as adenosine triphosphate (ATP):
• Utilized by direct calorimetry.
• Requires knowledge of generated heat, such as through the
differences in water temperature entering and leaving a chamber.
Indirect Calorimetry Measurement
➤ Measures oxygen consumption and carbon dioxide production.
Indirect Calorimetry Formulas
➤ Abbreviated Weir Equation: Resting energy expenditure =
oxygen uptake/consumption (VO
2
) + carbon dioxide output/
elimination (VCO
2
)
• Weir equation: Energy expenditure = VO
2
+ VCO
2
– Nitrogen (urine)
▶ Assumes FIO
2
+ FIN
2
= 1 (F = Fraction)
▶ Inhaled ambient air = 21% O
2
+ 79% N
2
+ less than 1% CO
2
➤ VO
2
= Oxygen uptake/consumption; VCO
2
= Carbon dioxide
output/elimination
Calculations for Estimating Physical Activity Energy
Expenditure
➤ Based on:
• Age, gender, weight, height
• Physical activity records and validated energy-expenditure tables
• Heart rate
• Motion sensors (e.g., pedometers)
