> [Bag breathing] Just until it's uncomfortable, usually a minute or two, depending on the size of the bag. If you do it a few times in a day, you might notice that it makes your [[skin]] (e.g., under nails) pinker, by improving circulation. > [At sea level, roughly how often would someone need to do it (2 mins duration) during a day to maintain a significant, noticeable elevation in CO2 levels?] 2 or 3 times a day will usually do it, you can check blood pressure to see its cumulative effect, but you should see a lingering increase of the pinkness of your nail beds. > [Do carbonated drinks have a significant effect on tissue concentrations of CO2?] In a crisis situation, it (or [[baking soda]] in water) can be helpful, but it's more effective to rebreathe in a paper bag. > [When you say several effects of CO2 shuts off glycolysis, do you mean anaerobic glycolysis or all glycolysis, if all glycolysis how does glucose enter mitochondria without breaking down to [[pyruvate]]?] Meaning the entry of lactate into the blood stream inappropriately, which would usually be called aerobic glycolysis, though you can't be sure how much oxygen is getting to the cells when CO2 is deficient, since its absence causes many problems in oxygen delivery and use. [So when CO2 isn't deficient glycolysis, meaning glucose to [[pyruvate]], is fine?] Yes, as part of oxidative metabolism, it's better than burning too much fat.