Testing and recording equipment (metabolic cart for indirect calorimetry).

The idea

A metabolic cart is a testing and recording system that measures oxygen uptake and carbon dioxide production to estimate energy expenditure by indirect calorimetry. The performer breathes through a mask or mouthpiece while sensors sample expired air; software records ventilation and gas fractions, then calculates oxygen consumption (for example in dm³·min⁻¹ or cm³·kg⁻¹·min⁻¹) and respiratory exchange ratio. It is used in sport to profile aerobic capacity, set training intensities and monitor recovery, and in exercise referral to quantify activity energy cost. Its value lies in objective, repeatable data, but accuracy depends on calibration, steady-state conditions and correct mask seal.

What earns the marks

• Identifies a metabolic cart as equipment for indirect calorimetry that measures oxygen uptake and carbon dioxide production.
• Explains that indirect calorimetry estimates energy expenditure from respiratory gas exchange rather than measuring heat directly.
• States that the cart records ventilation and gas concentrations and uses software to calculate oxygen consumption and respiratory exchange ratio.
• Applies the equipment to sport or exercise contexts such as aerobic capacity testing, training-intensity prescription or monitoring recovery.
• Recognises limitations: need for calibration, steady-state exercise, a good mask seal and controlled environmental conditions.

Common mistakes and how to put them right

• Confusing indirect calorimetry with direct calorimetry.

  Put it right: A metabolic cart estimates energy expenditure from respiratory gas exchange, whereas direct calorimetry measures heat loss in a chamber.

• Assuming the cart measures only oxygen.

  Put it right: It also measures carbon dioxide production and ventilation, which are needed to calculate respiratory exchange ratio.

• Treating the cart as a field-based tool for match play.

  Put it right: It is primarily laboratory-based because of the mask, tubing and calibration requirements.

• Ignoring calibration and steady-state conditions.

  Put it right: Without these, the recorded values are unreliable and cannot be compared across tests.

Exam tips

• Link the equipment to a named use, such as determining maximal oxygen uptake or prescribing aerobic training zones, rather than describing it in isolation.
• Use correct units and notation when quoting values, for example dm³·min⁻¹ or cm³·kg⁻¹·min⁻¹, and keep the superscript in cm³.
• When evaluating, give one strength and one limitation with a consequence, such as accurate energy-expenditure data but limited ecological validity in team sports.