RER is the respiratory exchange ratio. This is a metric we test during our VO2 max test. It is looking at the ratio of carbon dioxide (VCO2) produced to the amount of oxygen (VO2) consumed. This tells you when you go from using fat for fuel and energy to using carbohydrates.
HOW IS RER CALCULATED?
RER = VCO2/VO2
- VCO2 = amount of carbon dioxide produced/minute
- VO2 = amount of oxygen consumed/minute
WHAT DO THE NUMBERS MEAN?
RER tells you what you are using to make energy- is it fat or carbohydrate? If you are trying to burn fat, it is surprising, but you usually need to keep your heart rate lower. As your heart rate goes up, you go from burning fat to burning carbohydrates.
- RER = 0.7 . This means you are using fat for energy
- RER= 0.85. This means you are using a mix of fat and carbohydrates for energy
- RER= 1.0 or higher. This means you are using carbohydrates for energy. This is seen when you are doing high exercise intensity or maximal efforts.
RER above 1.0 happens when you go from aerobic to anaerobic metabolism. When this happens, you expel excess CO2 to buffer the increase in lactic acid from anaerobic metabolism.
HOW DOES RER RELATE TO VO2 TESTING?
On a VO2 max test we are looking for this inflection point. When does your RER = 1.0? It is at this point you go from aerobic to anaerobic respiration. This helps us also identify “maximal effort.” We want you to be above a RER of 1.0 for at least a minute. Many identify maximal effort as RER > 1.1, an objective sign you actually reached your maximal effort.
As for your exercise habits, looking at RER values helps you identify what activities you should target to burn fat vs. carbs. Low intensity activities use mostly fat for the energy source. As your exercise intensity increases, you rely more on carbs. For those in training, it is very useful to see where this occurs to help you know how to fuel and adjust your training regimen.
Hydration, diet, and recent exercise can influence RER, which is why we like you to do the test before you eat and have had 12 hours of no exercise. (See blog on how to prep for a VO2 test)
VO2 TESTING AT BIOHACKR HEALTH
We love this test. When you do a VO2 max test at our clinic, you will get a print out of your test results. You can see when you are burning fat vs. carbs and when you hit a RER of 1.0 and change from aerobic to anaerobic activity. It is fascinating to see how your body works. I personally was surprised- I burn no fat over a heart rate of 129.
This is a fantastic way to see your heart health, what your baseline is, and to help you train better for your goals.