If you are middle-aged or older, or planning on becoming a fit middle-aged adult in the future, it's critical that you exercise all three of your muscle fiber types - slow, fast, and super-fast.

MUSCLE FIBER TYPES
You have three types of muscle fiber that make up your "muscles," and this is sometimes called muscle composition. The average person has approximately 60 percent fast muscle fibers and 40 percent slow-twitch fiber (type I).

There are two types of fast-twitch muscle fiber. The fast muscle (what the researchers call IIa) moves 5 times faster than the slow. And the super-fast (IIx) moves 10 times faster. And there can be swings in fiber composition, (Muscle, Genes, and Athletic Performance, September 2000, Scientific American, Jesper).

The following chart shows that while there are differences in muscle fiber composition, muscle types can be developed based on the way they are trained.

MUSCLE FIBER COMPOSITION:

Sprinters have more of all three fiber types than average, and a higher percentage of the super-fast IIx. And endurance trained individuals have more slow muscle (type I). While we are born with slightly different muscle composition, the point is; super-fast muscle can be developed if exercised properly.

WHY IS THIS IMPORTANT?
Researchers show that anaerobic exercise (short, quick-burst, gets you out-of-breath fast) is the type of fitness training that naturally increases HGH (human growth hormone). And HGH is, without question, the most powerful anti-aging, and anti-middle-aging, body fat-reducing, muscle-toning agent made by your body naturally.

Yet, when most finish high school (perhaps with the exception of a few that compete in college and the small number that make it to the pros); many middle-age adults become slow-twitch exercisers beginning at age 20. And this is a mistake!

It's a mistake because muscle begins to waste away (atrophy) if it is not used.

Many adults continue developing slow muscle fiber with weight training and cardio at the gym, and with jogging. This typically only works slow muscle fiber. If you think about it, most adults start the atrophy process of fast muscle fiber (the wasting away of muscle) on over half of their muscle fiber ... beginning at age 20!

No wonder we have an obesity epidemic. This year, 650,000 Americans will hear their physician say, "You have diabetes."

The cure for the obesity crisis, the cure the middle-age somatopause (the middle-age metabolism slow-down), the cure for insulin resistance and (in many cases) diabetes -- is so simple, we keep missing it.

The cure is natural. And it's free. Middle-age adults should consider adding anaerobic workouts to their fitness training.

However, it can't be done overnight because the muscle fiber necessary to perform high-intensity anaerobic exercise has atrophied (wasted away).

THERE'S GREAT NEWS FOR MIDDLE-AGED ADULTS!
You can build back your fast-twitch muscle fiber (starting slowly at first) by performing plyometrics to build the fast muscle (IIa fiber) and performing sprinting types of training to build the super-fast (IIx fiber) to the point where HGH growth hormone can be released through exercise.

THE TAKE HOME
Middle-age adults need to be doing more than exercising their slow muscle fiber with weight training, cardio, and jogging. Don't neglect slow-muscle training however; this is 40% of your muscle fiber, and to a degree, it serves as a base for the development of the fast and super-fast muscle fiber.

It's always recommended to see your physician before beginning a fitness program. And even if you're in great condition, spend at least 6 to 8 weeks -- slowing and progressively -- building back fast and super-fast muscle fiber by adding plyometrics and sprinting types of training to your workouts.

More Information: National Library of Medicine. Phil Campbell is the author of "Ready, Set, Go! Synergy Fitness for Time-Crunched Adults" Pristine Publishers Inc. USA. A free Newsletter on this topic at www.readysetgofitness.com