Indirect Calorimetry:

At present the state of the art for energy consumption measures are Oxygen Consumption measures. Recent technical advances made this type of measurement more practical. Compared to the Douglas bag Method and the Metabolic Cart, recent devices (eg Cosmed K4 B2) are portable and allow for unconstrained ambulation which is important for subjects with motor disorders whose balance is inadequate for treadmill walking and for whom the use of a bicycle ergometer may be unattainable.

The essentials of this type of systems are a mechanism to measure the respiratory flow and a method of sampling the end tidal air to measure the oxygen concentration compared to the oxygen concentration compared in the ambient air. The Cosmed K4 simultaneously measures the raw values of percent O2 and percent CO2 in expired air, respiratory rate, tidal volume and heart rate. Combination of the measured values with walking speed allows for derivation of gross (GOC) and net oxygen cost (NOC).

From these raw data oxygen consumption and carbon dioxide production are calculated.

Advantages

Direct measurement of oxygen consumption end CO2 production (detects anaerobic metabolism)

Disadvantages

Expensive equipment

Cumbersome equipment