1. They Work as a Team
Limb muscles come in pairs. One muscle pulls, and the other muscle in the pair pushes the bones of the skeleton. Each muscle can only contract and relax; it can't push back. If you contract a muscle in your leg to bend your knee, relaxing the muscle doesn't push the knee back down. Instead, another muscle works to contract the other side to get the leg straight again. Each limb muscle has one specific job, and its partner muscle does the opposite.
2. Thoughts are Things to Muscles
You have control over the skeletal muscles, which are also called voluntary muscles. When you think about moving your arm, the muscles respond to your thoughts. Involuntary muscles like the heart don't require you to think, and that is really a good thing. Few of us could remember to breathe and make our heart beat continuously, especially when some days it's hard to remember where the keys are.
3. They Twitch at Different Speeds
Muscles contain two main types of fibers. Type I muscle fibers contract more slowly and have greater endurance. Type II fibers, including type IIa and IIx, give bursts of energy and don't have the same endurance as type I fibers. Each person has different ratios of these fibers in their muscle tissues. Long distance runners tend to have more type I fibers and sprinters have more type II.
4. Fixed for Life?
The scientific community has different ideas about whether new muscle fiber can be created. Some scientists believe that the number of muscle fibers is fixed from the time you make your way out of the womb. The difference comes in how you develop the fiber that you were given. Hypertrophy, simply put, is an increase in the cell size. Those that believe that hyperplasia can occur (an increase in the number of cells) think that it occurs only under specific circumstances.
5. Use it or Lose it
You need to move and challenge muscle tissue to keep it working at its maximum. The average inactive person in America loses about a half pound of muscle mass each year. As your muscles atrophy from inactivity, your legs and arms become less firm. Maintain an appropriate exercise program to prevent the reduction of your muscle size and increase your the basal metabolism rate. You can increase your limb muscles no matter how old you are.
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