Wearing the wrong shoes, especially for running, can cause foot injuries such as plantar fasciitis, which is common in those just starting to work out. Ballerinas who go on pointe must stretch their feet to increase flexion in their arches.

Your biceps muscle is located on the front of your upper arm and runs from your elbow to your shoulder. Performing exercises that require arm flexion, where you bring your forearm toward your upper arm, requires the biceps muscle to work to produce movement.

You might not need to do the middle splits frequently in your everyday life, but having the inner-thigh flexibility for splits comes in handy during a number of pursuits, such as martial arts, dance and rock climbing.

Trigger points are small, painful, tight nodules of muscle fibers buried in muscles. They contribute to chronic muscular pain, which in turn leads to joint pain and stiffness. Trigger points keep muscles tense and weak at the same time.

Stretching is an important part of your regular exercise routine and can improve your level of fitness and help you perform better. When done correctly, stretching should not cause pain or soreness.

A lack of muscular strength may cause the legs to feel weak or unable to support the body’s weight. It can be caused by many different disorders, such as bilateral sciatica, which affects the muscles in both legs. It may also be caused by a spinal injury.

The inability to walk as far and as long as you'd like to can be frustrating and even depressing. It may also be a sign your body is giving you to alert you of a health problem. Two causes of leg weakness after walking a short distance may be spinal stenosis or peripheral artery disease, especially as you age.

Scoliosis often creates an S-shaped curve that starts in the thoracic region of the spine. Without treatment, the spinal curves caused by scoliosis may worsen, causing pain, physical disfigurement, breathing difficulty and the need for bracing or surgery.

The hip abductor muscles include the gluteus medius, gluteus minimum, sartorius and tensor fascia latae (TFL) muscles of the buttocks and outer thigh. These muscles move the hip away from you in a sideways direction, which is called hip abduction. When these muscles are tight, it limits your hip mobility.

Your pelvic floor muscles provides support for your visceral organs, which include the urinary bladder and the lower intestines, according to Anthony Carey, owner and co-founder of San Diego physical-therapy practice Function First. They also control your continence and, in women, assist in birth.

If your ribs are cracking while stretching, pain is likely present as well. A rib fracture, costochondritis and sprain can all result in cracking if the rib cage is stretched. Consult your doctor for a proper diagnosis and treatment.

The deltoid is a three-headed muscle that consists of the anterior deltoid, lateral deltoid and the posterior deltoid. The anterior deltoid is involved in many chest-related movements. If this muscle becomes tight, it can alter your posture and can put you at risk for injury.