RER and Energy Expenditure

RER and RQ relationship

• RER ≈ RQ at rest and during steady-state submaximal exercise (not maximal)
• Definition: $RER = \frac{V<em>{CO2}}{V</em>{O2}}$
• RQ is the cellular/metabolic counterpart: $RQ = \frac{CO2\;produced}{O2\;consumed}$
• In steady-state exercise, RER closely tracks RQ, but RER can differ at higher intensities due to non-metabolic CO2 sources (e.g., buffering of lactate).

RER range and interpretation during rest and steady-state submaximal exercise

• RER values range from 0.7 (100% fats) to 1.0 (100% carbohydrates).
• 0.7 indicates predominant fat oxidation.
• 1.0 indicates predominant carbohydrate oxidation.
• Values between 0.7 and 1.0 reflect mixed substrate use and vary with exercise intensity and metabolic conditions.

What do RER values greater than 1 indicate?

• RER values > 1 indicate non-metabolic CO2 production, typically from buffering of lactic acid during high-intensity exercise, and/or non-metabolic CO2 sources such as hyperventilation.
• This occurs near maximal effort when anaerobic glycolysis is active and buffering maintains pH, causing excess CO2 that raises the RER above 1.0.
• RER > 1 is not a direct measure of substrate oxidation but a signal of high-intensity, glycolytic metabolism and buffering processes.

Caloric equivalents and energy expenditure (EE)

• RER levels have an assigned caloric equivalent value (kcal per liter of O2), allowing calculation of the rate of energy expenditure (EE) in the lab.
• Energy expenditure formula: $\text{EE} = VO<em>2 \times E</em>{<br /> obreak\mathrm{eq}}(RER)$
• Common approximate energy equivalents:
  • E{eq}(0.70) \approx 4.69\, \text{kcal L}^{-1}\, \text{O}2}
  • E{eq}(1.00) \approx 5.05\, \text{kcal L}^{-1}\, \text{O}2}
• Intermediate values can be interpolated between 0.70 and 1.00 (e.g., for typical resting-to-mlight-submaximal intensities).
• Example calculation:
  • If $VO<em>2 = 2.0\ \text{L min}^{-1}$ and $RER \approx 0.85$, then E{eq}(0.85) \approx 4.95\, \text{kcal L}^{-1}\, \text{O}_2}
  • Therefore, $EE \approx 2.0 \times 4.95 = 9.90\, \text{kcal min}^{-1}$
• Notes:
  • The exact kcal/L of O2 depends on substrate mix and measurement conditions; values are approximate and used for estimation in lab settings.

Key formulas (recap)

• RER definition: $RER = \frac{V<em>{CO2}}{V</em>{O2}}$
• Energy expenditure: $\text{EE} = VO<em>2 \times E</em>{eq}(RER)$
• Substrate interpretation: 0.70 => fat-dominant oxidation; 1.00 => carbohydrate-dominant oxidation
• Caloric equivalents: E{eq}(0.70) \approx 4.69\ \text{kcal L}^{-1} \text{O}2}\, , \; E{eq}(1.00) \approx 5.05\ \text{kcal L}^{-1} \text{O}2}