Fasting before Indirect calorimetry measure of submax exercise

[Justus Ortega]

Many of us use indirect calorimetry along side our other biomechanics measures. Many of us have our subjects fast and/or not intake caffeine for some period of time prior to testing. However, I have heard varying time frames for when to fast and or not ingest caffeine. 1, 2, 3, even 6 hours prior to the exercise.

I am wondering if someone can point me in the direction of a paper that investigates this issue (so I may cite them if needed) and,

what is the consensus regarding a proper of amount of time to have subjects fast prior to performing a submaximal exercise experiment?

How would this change if the experiment has ~ 1 hours of exercise over a 3 hours period of time?

[Ross Miller]

Re: Fasting before Indirect calorimetry measure of submax exercise

I've asked the exercise physiologists in my unit this same question and the consensus seems to be:

- The minimum fasting time to provide an adequate control is about 3 hours
- An overnight fast is overkill but is largely done for convenience (stop eating at a normal time then do the test first thing in the morning)
- If not controlled, it won't necessarily affect the overall metabolic rate very much, but can have a big effect on substrate oxidation
- Same story for caffeine
- No need to worry about drinking water pre-test unless specifically studying hydration

I don't know this literature well enough to give any key references, but here's one I found quickly on running (maybe they cite some of the key earlier references):

https://www.physiology.org/doi/pdf/10.1152/jappl.1986.61.4.1363

"Postprandial" (relating to the period after a meal) seems to be the term commonly used for this; I didn't have much luck searching for e.g. "fasting metabolic rate walking".

Ross