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Muscle is a bundle of tissue that is capable of contracting. The primary functions of muscles are to generate force and cause motions. Your body has more than 600 different types of muscles. Muscles also contribute to 40 to 50 percent of your weight. Some muscles can be controlled consciously, while others are controlled automatically by your brain. There are three types of muscles: skeletal, cardiac and smooth. Each type of muscle has different characteristics and essential roles.
When people talk about muscles, they are usually referring to skeletal muscle. This type of muscle is attached to your bones through tendons, and it is the most abundant tissue in your body. The contraction of skeletal muscle causes the diverse movements of your skeleton. Skeletal muscle is a type of muscle that you can control voluntarily. The pectoralis major, biceps brachii, deltoid, rectus abdominis, and gastrocnemius are examples of skeletal muscle.
Cardiac muscle is a type of muscle tissue that is only located in the walls of your heart. Because your hearts beats more than 100,000 times and pumps 7,200 liters of blood a day, cardiac muscle is designed to be highly resistant to fatigue and deliver consistent movements. The contraction of cardiac muscle fibers generates the force that squeezes your heart -- which effectuates blood flow throughout the rest of your body. Since it is involuntary, you do not have direct control over it.
Smooth muscle is found in your hollow organs and blood vessels. Like cardiac muscle, smooth muscle cannot be controlled consciously. Its actions are automatically controlled by your brain. Although smooth muscle is not able to contract as fast as skeletal muscle, it is designed to be very elastic. Good elasticity is required to support the constant flow blood and food through your blood vessels and stomach. Smooth muscle is found in organs such as the uterus, bladder and gastrointestinal tract.
Exercise and Muscle Development
Since you have direct control of skeletal muscles, you can develop them by performing physical exercise. Strength-training exercises allow you to increase the strength and size of your skeletal muscles. Performing regular exercise also benefits cardiac and smooth muscles. Regular exercise helps reduce your risk of obesity -- which is strongly linked to coronary heart disease. The accumulation of fatty substances in your arteries is the main cause of coronary heart disease. Performing regular exercise enables your heart to pump blood more efficiently throughout your body. A 2002 study published by the вЂњJournal of the American Medical AssociationвЂќ showed that physical activities such as running and weight training reduce your risk of coronary heart disease.