Does fat burning really stop during intense physical exertion?
The RER increases with continuous intensification of the load (e.g. during spirpergometry).
There are several hundred publications in the literature describing that fat burning stops during intensive physical exercise! The authors have in mind studies such as the one shown in the front part of the figure below. This conclusion is drawn because the respiratory quotient, RQ – or better the respiratory exchange rate (RER), the quotient of exhaledCO2 to inhaled O2 rises to 1, usually even above one. (For interpretation of the quotient, see“indirect calorimetry“).
Measured values misinterpreted!
Sorry, this is a misinterpretation of measurement results, as we have shown in a publication (Lotz et al, 2019). The error results from the fact that theCO2 that is exhaled during intensive physical exertion as a result of buffering the lactate is simply neglected. In our test subjects, an average of 21% of the exhaled CO2 came from buffering during maximum exercise!
The RER corrected for the contribution of buffering remains unchanged!
This clearly shows that fat burning continues to function almost unchanged, even if the test subjects are exposed to maximum loads in a spiroergometric test.
The comparison of the two images shows that the calorie consumption from fatty acids appears to drop to zero at maximum exercise intensity if the buffering of lactate by bicarbonate is not taken into account. The release of bicarbonate from the blood is a source of exhaledCO2, which must not be neglected under any circumstances. Fatty acids continue to be used to a considerable extent for energy production, even at maximum exertion.
RER with lactate in steady state also above LT2 well below 1
It is also important to note that spiroergometry has often shown that fat burning occurs during exercise above the 2nd lactate threshold if the lactate concentration is measured approx. 10 minutes after reaching a steady state. If the lactate concentration does not change, no additional CO, which is produced from the buffering of the lactate, is released during respiration, the RER remains in the normal range and can be used as a measure for the distribution of fatty acids or glucose for energy supply!
No more reason to move slowly!
Sorry if we have now spoiled your main argument against jogging at a very low load! Others are worse off; they now have to rewrite their textbook articles and their websites!