[Ed. note: Last Saturday night, at UFC 156, behemoth Dutch kickboxer Alistair Overeem got knocked out standing up by Antonio "Bigfoot" Silva after battering Silva for the the better part of two rounds. By the beginning of the third round, it was clear Overeem, who has been denying accusations of steroid abuse for years, was completely exhausted, that his muscular body was betraying him, and that he was incapable of fighting off anyone, much less a 260-pound mauler like Silva. We talked to Dr. Michael Kelly, a sports-medicine specialist, part-time ringside doctor and the author of the book Fight Medicine, to explain how someone who looks like the comic-book portrait of health and vitality could collapse so suddenly and with so little resistance.]
Dr. Michael Kelly: The initial explosive energy with muscle—the anaerobic burst of energy—is usually fueled by glucose, or glucose in the muscle called glycogen. But it’s a very short-lived source of energy. There are slow-twitch and fast-twitch muscle fibers. People tend to spend a lot of time building the size of the muscle; often what they’ll do is build up the fast-twitch fibers and sacrifice the slow-twitch fibers, or smooth muscle versus striated muscle. What happens is the striated muscle can use glucose effectively for a short period of time, but then it tends to burn out real quick. Whereas the smooth muscle, the slow-twitch fibers, they tend to use other sources of fuel very effectively, what we call oxidative phosphorylation or aerobic metabolism.
If you look at athletes where their body looks more like a bodybuilder’s, like Overeem's, it’s because they built up these fast-twitch muscle fibers at the expense of the slow-twitch. In the muscle itself, the proportion of muscle fibers that can use that slower-burning energy is much smaller.
In effect, the explosive muscle fibers don’t have a lot of endurance. They tend to burn out quick because the percentage of energy used is predominately glucose over fat in your blood stream. Glucose goes away faster because it’s a very inefficient way of utilizing energy. Your muscles only have so much glycogen stored in them, and it takes time to replenish that. So it’s a combination of limited stores and very inefficient use, which results in the glucose burning very quickly and burning out faster.
Read the rest at FIGHTLAND.