Statistics indicate that between 65% and 80% of all recreational and competitive runners experience some type of overuse injury annually. Such injuries include patellofemoral knee pain, illiotibial band syndrome, shin splints, Achilles tendinopathy, plantar fasciitis, and stress fractures. The vast majority of such injuries, ~80% affect the lower-leg, with nearly 40% occurring at the knee. Unfortunately, science and medicine have yet to truly understand the mechanisms behind such injuries.

Researchers recently reviewed the literature over a 28 year span from 1980 to 2008 and concluded that two mechanisms appear to underlie all lower-leg injuries. First, a small number of studies implicated "atypical foot pronation mechanics." Pronation, which occurs during the stance phase of gait as the foot flattens causing internal rotation of the tibia and femur, is essential to generating energy for the next stride. However, excessive or insufficient pronation leads to poor energy production and consequently to excessive motion about the foot and knee.

Second, and more prominent, researchers uncovered a growing number of studies that suggest "inadequate hip muscle stabilization" leads to a majority of overuse injuries. Because the hip muscles, specifically the gluteus medius, minimus and maximus stabilize the leg during gait, poor strength or conditioning of these muscles results in excessive stress at and below the knee.

Recent studies have shown that improving hip muscle strength reduces the incidence of knee pain in runners.  

Ferber, R., et al (2009) Suspected Mechanisms in the Cause of Overuse Running Injuries: A Clinical Review. Sports Health.