I love podcasts. I get tired of music pretty quickly when that's all i listen to on the road, at home, during practice, etc. I find that podcasts are a great way to learn new information, especially when I'm stuck driving. Here is a new podcast I've been listening to, this episode comparing the two types of muscle fibers, fast-twitch and slow-twitch.
Type I - slow-twitch muscle fibers
These muscles are for endurance events and more resistance to fatigue
These muscles are smaller - an endurance runner will look lean but can go forever while a sprinter will look ripped but poops out fairly quickly
These muscles have more mitochondria (biology lesson!) - mitochondria are responsible for creating the energy for the muscle to contract
These muscles contract slower than fast-twitch muscles (hence the names...)
These are your "aerobic" muscles
Type II (a and b) - fast-twitch muscle fibers
These muscles are susceptible to fatigue very quickly
These muscles are larger - what makes you looked "jacked"
These are your "anaerobic" muscles
These muscles don't require oxygen to fire, they rely on other compounds within your body
This leads to a large production of lactic acid (the burning feeling in your muscles you'll feel after doing a number of sprints)
My Two Cents:
The distinction between these muscles is very important and in all sports it is important to understand how to train correctly based on your muscle type.
I am a muscle and energy system nerd and could go on forever about this, but to make sure I don't bore you I'll keep it short. Your fast-twitch muscle fibers can last for about 60 seconds before starting to fail (training can alter this time). So in a sense of swimming, that covers most of your 50's and 100's. Anything over 60 seconds and you will start to use your slow-twitch muscles. This is why training correctly is so important.
Disregarding the importance of "getting in your 10,000 hours" (to master the skill of swimming, a rule described by Malcolm Gladwell) a sprinter should not be doing much long repetitive swimming! For the most part, you either have mostly fast-twitch, or mostly slow-twitch muscles. You will not have equal parts of both muscle types in your body. So, doing long aerobic sets where a 50-freestyler holds a slow "aerobic" pace could actually inhibit their fast-twitch muscles.
This is why we have seen such a drastic change in how swimmers train since the 1980's and 1990's. It's no longer about cramming in as many yards as you can. Now it is more, "don't count the yards, make the yards count." Unless you are a distance swimmer of course.
If you have comments or questions on that theory of training, reach out to me! I love talking about this kind of stuff.
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