Voluntary muscles are one of three types of muscle in the body; smooth and cardiac are the other two types. There are more than 600 muscles in the body, and each falls into one of these categories. Smooth muscles are involuntary; cardiac muscles make up the muscles in the heart; voluntary muscles are controllable by your brain — and these are the muscles you use to perform activities.
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Major Muscle Groups
The muscles of the chest, back, shoulders, abdominals, arms, and legs make up the body's major muscle groups. Listing all 600-plus muscles in the human body would be difficult, not only because there are so many, but because people disagree on exactly how many there are. The major muscle groups are fairly standard, however, and these can broken down further into component muscles — for instance, the arms can be listed as the biceps and triceps.
The muscles of the chest are typically called the pecs, short for pectorals. The two significant muscles of the chest are the pectoralis major and pectoralis minor. The pecs account for movement in the shoulder and shoulder blades, also called the scapulae.
There are many muscles of the back. The main muscles include the erector spinae, which run the length of the spine and neck, the latissimus dorsi (middle back), the rhomboids (upper back), and the trapezius (upper back and neck). The back muscles are important for posture, as well as movement of the shoulder blades, spine and shoulders.
The shoulders join the back and chest with the arms. The name of the shoulder muscles is the deltoids. The deltoids consist of three parts: the anterior (front), medial (side), and posterior (rear). Together, these muscles account for shoulder flexion, extension, and lateral flexion, which means moving the shoulder forward, backward, and to the side.
The muscles of the arms can be separated into the upper arms and forearms. The upper arm muscles include the biceps on the front, and the triceps on the back. These muscles move the elbow. The forearm muscles, in the lower arm, move the wrist and rotate the forearm.
The main muscles of the legs include the quadriceps of the front of the thigh, the hamstrings on the back of the thigh, and the calf muscles of the lower leg. The calf muscles include the gastrocnemius and the soleus. Other leg muscles include the adductors of the inner thighs, and the abductors, which are the muscles of the glutes and outer thighs. The glutes, however, are considered core muscles, as they assist with torso stabilization and balance. Other core muscles include the spine, pelvic floor muscles, and the muscles near the spine.
The muscles of the stomach include the rectus abdominus, transverse abdominus, and the internal and external obliques. The rectus abdominus, nicknamed the six-pack muscle, is the visible muscle. The obliques are on the sides of the stomach, and the transverse abdominus is below the obliques. The transverse abdominus compresses the abdominal organs.
Other Voluntary Muscles
There are some important muscles, of course, beyond the major muscles. The muscles of the face, neck, and tongue are useful voluntary muscles that allow you to eat, support and move your head, and make facial expressions.