The rectus abdominis is a large muscle in the center of your abdomen that extends from your ribs to the front of your pubic bone. Injuries to this muscle result in varying degrees of abdominal strain.

You couldn't open or close your mouth without your masseter muscles. Imbalances or tightness of the masseter on each side of your jaw can contribute to temporo-mandibular joint, or TMJ disorder. Characterized by pain, stiffness and clicking in your jaw, TMJ can cause headaches and neck pain.

Squats are a whole-body workout. When you do them properly, they build nearly every muscle you have. Do them improperly and you run the risk of real pain or injury. Even if you're a squatting pro, you might still suffer severe leg cramps after squats. Cramps are a bit of a mystery.

You may be fearful of drinking seltzer water because you heard it is bad for your health. Negative ideas about seltzer include the fact that it may irritate your stomach, erode the enamel on your teeth and cause osteoporosis. But seltzer water isn't much different from regular water.

Leg cramps are painful contractions of the leg muscles; the incidence of leg cramps increases with age. Often there is no official cause for the leg spasms; however, there are conditions or medications that can cause them. If the leg cramps become persistent, a doctor's visit may be needed to determine the cause.

A lumbar disc herniation occurs in the lower back and results in symptoms such as sharp or dull back pain, muscle spasm, leg weakness and sciatica. Lumbar disc herniations are common problems, affecting an estimated 1 to 2 percent of Americans, according to a September 2006 article in "

Inversion boots, otherwise known as gravity boots, allow for complete, inverted suspension from a stabilized horizontal bar or inversion rack. The boots strap around the ankles and attach to the bar, allowing you to hang safely, upside-down and otherwise unsupported.

Muscles contract when being used and will relax or loosen when not in use. However, your muscle may sometimes stay tight or suddenly involuntarily contract. An involuntarily contracted muscle is often called a cramp or a spasm. Muscle cramps can occur for different reasons.

The diaphragm and longitudinal muscles of the stomach play an important role in everyday functions. The diaphragm is responsible for supplying the force behind every breath you take; your longitudinal muscles help stabilize your body when you are moving around.

Plantar fasciitis is a painful inflammation of the plantar fascia, a ligament on the bottom of your foot that connects the heel with the toes and supports the arch. Pain occurs in the arch of the foot and near the heel, and is worse in the morning until you have walked for a while.

Sciatica is a painful condition that can also lead to weakness and numbness in the low back, hips and legs. The first step in treatment is to diagnose the underlying problem that is causing the sciatica nerve to be irritated.

Groin muscle strains -- sometimes called pulled muscles -- are painful injuries, caused by forceful movements of your leg, such as stepping off a curb while off balance or falling with your leg stretched out to the side. Female athletes whose sports require running, jumping and kicking are prone to these injuries.