We know that MJ had a high fast to slow twitch muscle ratio due to his explosive athleticism. If so, we would expect him to tire out fast. But that is not the case. He averaged over 40 minutes per game.
How can an individual with high fast twitch muscle composition at the same time possess great stamina?
Say MJ sprinted and slam dunked. He then used all his muscle fibers both fast twitch and slow twitch. After that followed say 3 minutes of running around at moderate speed. During this time his fast twitch fibers were recovering and he was only using his slow twitch fibers. After the 3 minutes had passed he was ready for another sprint and slam dunk. This cycle could then be repeated for a long time.
I think you're vastly underestimating the endurance capabilities of fast twitch muscle fibres. A person's proportion of muscle fibre types is not as limiting as you think it is.
Type I ("slow twitch") muscle fibres generate ATP (the fuel that the muscle uses) primarily through the aerobic energy system, and have a slower speed of contraction and burn energy more slowly than type II.
Type II ("fast twitch") muscle fibres generate ATP through both the aerobic and anaerobic/glycolytic energy systems (with type IIb being more anaerobic than aerobic), and have a faster maximum speed of contraction and can burn energy at a higher rate than type I.
Both fibre types are capable of exerting indefinitely at a low enough intensity that their energy systems can keep up with the demands placed on them. Type II definitely do not become exhausted with just any use, rather they would only become exhausted when the energy demands placed on them are sufficiently high that the energy systems fuelling them cannot keep up. But type I fibres would also become fatigued through the same use.
So Michael Jordan is perfectly capable of playing a game of basketball for 40 minutes, as the intensity of this is low enough that his energy systems can keep up with it. If you asked him instead to sprint from one end of a basketball court to the other, dunk a ball, sprint back to the first end and dunk again, and keep repeating this back and forth as quickly as he could, then he would certainly tire out in a much shorter period of time because the intensity is higher.
Another good comparison between the effects of having different proportions of muscle fibre types would be to compare training effects of different types of exercise on people with mostly type I vs mostly type II fibres. If you trained them all for jumping ability, you'd expect the people with more type II fibres to end up being better jumpers, but those with mainly type I fibres would still be capable of jumping. If you trained them all to run a marathon, you'd expect the people with more type I fibres to end up being slightly faster distance runners, but those with mainly type II fibres would still be capable of running the marathon.
