01What it measures
Indirect calorimetry estimates metabolic rate from respiratory gas exchange rather than heat directly. A known flow of air passes through the animal chamber; the difference between incoming and outgoing gas concentrations gives the oxygen consumed (VO₂) and CO₂ produced (VCO₂) per unit time.
02RER & substrate use
The respiratory exchange ratio (RER) is VCO₂ ÷ VO₂ — a window into which fuel the animal is burning. Tap a fuel state to see where it sits:
RER near 0.70 means fat oxidation; near 1.00 means carbohydrate. Because RER tracks substrate selection, it is central to obesity, diabetes, cardiovascular, and aging research.
03From gas exchange to energy
VO₂ and VCO₂ combine into energy expenditure (EE). Because the caloric value of oxygen depends on the fuel mix, EE is computed from both gases — not oxygen alone.
04Getting a clean measurement
- Stable gas flow — set to animal size so the chamber turns over fast enough to resolve change.
- Sensor calibration — O₂/CO₂ referenced to standard gas and fresh air before a run.
- Adequate sampling — per-second reads catch transients; per-animal means ± SD summarise steady state.
05How ConductMetabolism implements it
The measurement system included with the Rodent Metabolic Treadmill reads O₂ and CO₂ to 1 ml resolution per second, computes RER and EE live, and exports per-animal statistics. The same system measures at rest or during graded exercise on the treadmill.
