Does ATP production increase with oxygen availability?
The factors limiting ATP production are the rate of fuel (glucose, fats, amino acids, etc.) metabolism and its efficiency (ATP molecules per fuel molecule).
It is possible to produce ATP with zero oxygen by the glycolytic pathway; if this were not true, there would be no anaerobic organisms on Earth (which there clearly are). Muscle can do this too for short periods of time, producing lactic acid. In fact, many researchers believe that this pathway can produce ATP the fastest of any route of glucose consumption, even though it is least efficient. In other words, the number of ATP per glucose is small (only 2), but glucose &quot;flows&quot; through this pathway so fast that it is still generated faster than by respiration, which produces 30-32 ATP per glucose, but can process far fewer molecules of glucose per second. The actual rate of ATP generation by mitchondria is only limited by O2 concentration, in a chemical kinetics sense, in hypoxia, i.e. when a tissue does not have adequate blood supply, as in certain tumors.
The main effect of oxygen availability is likely size scaling--if you have more O2, you can get it through a larger body more easily. It's not that the muscle cells themselves generate more energy, it's that you can supply more muscle fibers that are farther from the lungs/gills/whatever. That's why in the carboniferous period on Earth, where there was considerably more O2, many animals (particularly invertebrates) were much larger than they are today.