So why am I talking about chickens and your mom? Well, what I am really talking about is muscle fibers and the different types of fibers. So we know there are 3 types of skeletal muscle fibers right? Type I, and Type IIa, and Type IIb. Type I's are the slow twitch. those found in middle to long distance runners. Type IIb are the big muscle fibers that you see in sprinters and type IIa are somewhere between these two. Unless your are a sprinter, you want lots of I and IIa fibers! Did you know when we are born we have about 40% type I fibers, 45% type II fibers(35% IIa, and 10% 2b) and 15% undifferentiated fibers.
Well what about the chickens you are asking?It is trivia, but it will help you understand muscle fibers! Here's the story on chickens: Chickens..... we mostly think about breast meat and drumsticks. Well, what about them? What fiber type do you believe is in each type of muscle? Well, breast meat as we know is a huge set of muscles, they flap really hard, but can't sustain flight for more than say about 10 seconds if at all but they sure might try to fly? Does that sound familiar to you Sprinters? So breast meat is type IIb muscle fiber equivalent, capable of short burst of highly explosive energy release, but not sustainable. The drumsticks are type I equivalent muscle fibers, the normal posturing, running around the chicken house muscles that can last for hours without much fatigue.Hmmm, sounds like what distance runner might have?
What about your Mother you are asking? Ok, so remember those percentages of fibers I discussed above? Well the muscle fiber type is determined by the X chromosome, so if you are a male, the X Chromosome came from your Mother, if you are a female it came from either your mother or your father, but if it was from your father, you can thank your grandmother instead, as that is where his X Chromosome came from! As a side note, those mitochondria we all want to have for ATP generation and generation of that beloved VO2max are also inherited on the X chromosomes! Hit rewind and read that again to be sure you got it!
The take home for you to realize, is that your ratio of fiber types are mostly predetermined, but there is a pretty big swing available for those undifferentated 15% fibers that can be either type I or II and also you should realized that it is those type IIb fibers that have the most capabilty to become type IIa-like fibers with proper training. Type IIa fibers are the ones we are training when we do the high intensity interval sets.
Be sure you let your Momma know about this next time you sit down with her and thank her or grandma for the X chromosome goodies (or quietly tell her it's her fault you run like a tortoise)!
Jeff Bangle, DVM