You NEED to know your muscle fiber type so you can TRAIN most effectively for your muscle fiber type.

For me, it's taken me a LOT of years of training to determine what really works best in each muscle group in my own body and for shaping my overall training methods.

When I started training, I was a long-distance runner, so I started off with well-developed slow-twitch muscles. This has led me down the path of a lot of strength-endurance type of training.

I have a good tolerance for lactic acid (i.e. lactate), so higher-rep range training and using longer time-under-tension training is very effective for me. Plus, I can actually maintain good muscle function in acidic conditions without throwing up (which is a nice bonus, especially when I do high-rep squats ;).

What I've also found with testing is that top-end strength is a bit tougher for me. I don't have a whole lot of Type 2B "explosive power" muscle fibers, so "power" exercises like Olympic lifting are a challenge for me.

I don't have the level of explosiveness that some people have.

I do train power exercises so that I still develop decent power and explosiveness, but it's not my physiological "calling," so to speak and I know I'll never be able to compete with somebody who has a more generous helping of those in a power sport.

(Put that same person on a long-distance heavy loaded carry with me, though, and I will bury them...the pic below is me finishing off a 2-mile walk with a 145 lb sandbag on my back)

I have a decent amount of Type 2A muscle fibers (which are still relatively powerful but have more endurance and recover faster than Type 2B fibers), so when I train for muscle growth, I tend to do much better on higher-volume training programs.

Granted, even if your predominant type is slow-twitch (or fast-twitch), you'll still have variances in your individual muscles in terms of fiber make-up.

For example, in just about everybody, the hamstrings are mostly fast-twitch because of their function in the body (hip extension, knee flexion and eccentric shock-absorption in running).

So you still definitely DO still need to train all your muscle fibers types to some degree, regardless of your predominant fiber type and you still need to work with heavy, basic exercises in order to maximize the size of your fast-twitch fibers that you do have (even if you don't have a lot).

However, knowing what your muscles mostly consist of allows you to better target your training to what your body is going to best respond to.

Your Fiber Type is Your "Muscle Horoscope"...

Think of it like astrology, only based on science instead of BS... ;) and it's something you can actually get useful, practical information from.

The next step is learning how to train for your specific muscle fiber type makeup, to maximize the muscle and strength you can build...

SLOW TWITCH

If you think you're primarily slow twitch, click here. (very good endurance but have a hard time building mass and strength)

FAST TWITCH

If you think you're primarily fast twitch, click here. (build muscle and strength easily)

MIXED FIBERS

If you think you have a pretty even mix of fibers, or if you're not sure which category you fall into, click here. (a mix of strength, muscle and endurance)