You may have heard the term respiratory quotient from spiroergometry, the breath gas analysis during exercise, but what does it actually mean and what is its meaning? To understand this, you have to take a closer look at spiroergometry.
During spiroergometry, the inhaled and exhaled respiratory gases (O2 and CO2) are analyzed using a breathing mask during exercise (usually on a bicycle ergometer or treadmill), and the respiratory volume (V for volume) is measured. Today, this is done with so-called breath-by-breath systems, which are able to analyze every single breath.
Differentiated terminology
The respiratory quotient is the ratio of carbon dioxide released (VCO2) to oxygen absorbed (VO2) during the entire respiratory cycle. Strictly speaking, the respiratory quotient (RQ) stands for the inner respiration in the cell (metabolism), which is why one also speaks of the respiratory exchange rate (RER) as a designation for the outer lung respiration, which is measured with spiroergometry. We will see later why this must be distinguished.
Fats or carbohydrates?
The respiratory exchange rate can be used to calculate exactly how many fats or carbohydrates are burned at what intensity of exercise during exercise or rest (measurement of the basal metabolic rate). This works by knowing that fats, proteins and carbohydrates provide different RER values:
Fats: 0.7
Proteins: 0.8
Carbs: 1.0
These ratios come from biochemistry and stem from the respective reaction equations and the VCO2 and VO2 ratios. Using these numbers, one can calculate actual fat burning and carbohydrate burning rates. Thus, an assessment of the energy metabolism is possible.
Limits and influencing factors on the RER
As already mentioned, the RQ and the RER must be strictly distinguished, since the metabolism in the body (during exercise) does not always correspond to the RER (the values measured for VCO2 and VO2 via the breathing mask). Up to a certain intensity of exercise, the RER corresponds to the metabolism in the body. This is the case right up to the point where lactate buffering starts in the body due to the increased intensity of exercise and excess CO2 is exhaled. Up to this point in time, the energy metabolism can be meaningfully calculated, beyond that no more.
There are also various influencing factors on the RER
- Eating habits before the test
- glycogen storage size
- Breathing technique (hyper and hypoventilation)
Eating behavior influences the RER, since the administration of simple carbohydrates increases the insulin level and the body automatically resorts to the energetically more favorable carbohydrates. Conversely, depleted glycogen stores simulate good fat metabolism, which is actually not there.
In summary, it can be said that the RER or RQ can be used to assess the energy metabolism in the lower stress range and to measure the basal metabolic rate if standardized preparation is taken into account, but should not be overestimated and must always be considered in the differential diagnosis.
