Pronation is the inward roll of the foot. This is a necessary function of the anatomy of the foot that provides support, balance, and cushioning for the body during motion. In a normal gait cycle the heel comes in contact with the ground, then pronates slightly as the foot flattens out, and finally pushes off from the middle to inside of the forefoot to allow forward motion. Many runners (about 70%) over-pronate, where the foot flattens out too much and the inward roll becomes severe.

Far less common than over-pronation, under-pronation (or supination) is when the foot fails to roll inward and instead the body weight remains along the outer edge of the foot. Supination motion is natural during the push-off phase, when the heel leaves contact with the ground and the body balances along the entire forefoot as it propels the body forward.

The plantar fascia is the dense connective tissue located at the bottom of the foot where the heel and arch meet. It is most frequently caused by over pronation. If the foot flattens or becomes unstable during running/walking, the plantar fascia may pull away from the heel bone. This results in pain and/or swelling primarily where the heel and arch meet. Pain is most noticeable when pushing off of the toes. Repeated tearing and damage to the plantar fascia can lead to the development of a "heel spur" on the calcaneus (heel bone).

The iliotibial band (IT Band) is a thick, fibrous band of tissue extending down the outside of the leg from the hip to the outside of the shin bond (tibia) just below the knee. The IT Band provides stability and assists in flexion of the knee. ITBS is often due to overuse and sudden increase in mileage. Persons with pronation issues or who are bow-legged are more susceptible to ITBS.

Shin splints are caused by fatigue and overuse of the muscles along the shin bone (tibia). Most often they are along the inside of the shins and toward the lower half of the leg. It may be caused by training regimen, but is often a result of running or jumping in shoes that are broken down or are improperly fit.

Patellofemoral Pain Syndrome (Runners Knee)
Patellofemoral pain syndrome is pain behind the kneecap.  It has been given many names including patellofemoral disorder, runners knee, and chondromalacia.  Patellofemoral pain syndrome can occure from overuse of the knee in sports such as, running, walking, jumping, or bicycling.

Achilles Tendonitis
The Achilles tendon is a band of tisse that connects the heel bone to the calf muscle of the lower leg.  Achilles tendonitis occurs when this band becomes inflammed, causing pain at the back of your leg near the heel.  Achilles tendonitis can be caused by: Overuse of the achilles tendon, tight calf muscles, lots of uphill running, increasing the amount or intensity of training, overpronation, wearing high heels at work then moving to a low heeled shoe for exercise, or sudden explosive activity (during a jump or sprint).

Muscle Strain
A strain is a stretch or tear of a muscle or tendon, and are commonly known as "pulled muscles".  Muscle strains are usually caused by forceful contraction (tightening) of the muscle during an activity.

Stress Fracture
A stress fracture is a hairline crack that can occur in bones from repeated or prolonged use.  Stress fractures are overuse injuries.  The majority of sress fractures occur during activities such as running, jumping, or dancing.

Ankle Sprain
An ankle sprain is an injury that causes a tear or stretch of one or more ligaments in the ankle joint.  Sprains can be graded, I, II, or III depending on the severity of ligament damamge.  A sprain is caused by twisting your ankle.  Your foot usually turns in or under, but may turn to the outside as well.