"Skeletal muscle" is a term used to describe muscle in your body that attaches to bone and helps you perform everyday movements and control your posture. It is under your conscious control and differs from your cardiac muscle and the involuntary smooth muscles that control a number of vital organ functions. When you exercise, your skeletal muscles undergoes several important changes.
Basics
While we tend to think of skeletal muscles as relatively simple structures, each cell in your muscle tissue actually contains hundreds of thousands of tiny, interlocking fibers and smaller structures called filaments. Two particular filament types, called actin and myosin, attract each other and form interwoven bridges that give your muscle its strength. Certain muscle fibers, called fast-twitch fibers, contain an energy-rich form of myosin and fatigue relatively quickly during exercise or other use. Other fibers, called slow-twitch fibers, contain a lower-energy form of myosin and fatigue relatively slowly when you exercise.
Size and Nerve Function
When you lift weights or engage in other muscle-building activities, you increase the amount of myosin and actin inside the fibers of each affected muscle; in turn, this increase causes your muscles to gain size or mass. This process, which typically takes place gradually over a period of weeks or months, is known as hypertrophy. Regular participation in exercise also increases the efficiency of the nerve signals that pass between your muscles and your brain and allow you to consciously and accurately control your movements.
Muscle Fiber Activity
By engaging in certain types of activities, you can control exercise's effects on your fast- and slow-twitch muscle fibers. For instance, regular performance of activities that require aerobic endurance will lead to an increase in the size of your fast-twitch muscle fibers. If you perform moderate types of muscle-building, you will increase the size of both your fast- and slow-twitch muscles. However, if you engage in intense muscle-building activities, you will only increase the size of your fast-twitch muscles. Despite common conceptions, engaging in certain forms of exercise will not allow you to convert fast-twitch fibers into slow-twitch fibers or vice versa.
Anti-Aging Effects
According to a study conducted at McMaster University Medical Center in Ontario, Canada, long-term regular performance of muscle-building exercises can help partially offset age-related loss of skeletal muscle in older individuals. At the beginning of the study, participants over the age of 65 were roughly 59 percent weaker than participants under the age of 35. By the end of the study, this strength gap had dropped to 38 percent. In addition to direct increases in muscle size, exercise appeared to alter the genetic expression of certain traits for muscle strength.
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