> You can walk or jog at an easy effort for a long time and eventually your muscles will get tired and sore, Perhaps this is because your lungs are getting tir

> You can walk or jog at an easy effort for a long time and eventually your muscles will get tired and sore, Perhaps this is because your lungs are getting tired--I wonder if there's lactate buildup in the lungs. I'm no biologist, but my understanding is our muscles need oxygen, to get this oxygen we need to do many things--breathe more air (v02 max), more efficiently distribute the oxygen through the body (heart rate and stroke volume), and finally the oxygen is delivered to the mitochondria in our muscles, so increased vascularity (vein size), would help. Our muscles also need other supplies of energy--glycogen to produce atp or ketosis. I suspect if we're glycogen dependent we get tired a lot faster. There are many hyper marathon runners that are in ketosis, like Goggins: > He was able to run 101 miles in 19 hours and 6 minutes—despite never having attempted to run a marathon previously I think if the heart gets tired, you die, so the brain probably stops that from happening. You can die of exhaustion, many atheletes just die early from heart attacks. Anecdotally, if I don't get lactate buildup in my muscles, since being in ketosis I don't really get tired. I went from a 5 minute bike being difficult, to a 1 hour bike and not getting tired near the end.