Correlation Between Contractile Properties of Quadriceps Muscle and Functional Performance in Runners With Patellofemoral Pain Syndrome

Running is one of the most widespread activities during which overuse injuries of the lower extremity occur. Long-distance running is very popular among participants of recreational sports . In 2008, about 11.5% of the population in the United States ran and, of this group, 3.4% ran on average two times a week or more. In Europe, it is estimated that 36% of the population aged 15-65 years are recreational runners.

Most running-related injuries occur in the lower extremities. The most common anatomical site of running injuries is the knee.

Risk factors for running injuries have been well investigated , However, because of the heterogeneity of the studies (e.g., definition of injury, recreational or elite runners, and short- or long-distance runners), no clear overview is available regarding the most important risk factors for running injuries. Increased training volume per week in male runners, and a history of previous injuries for runners, are known significant risk factors for running injuries.

The various purported risk factors for running injuries are commonly divided into intrinsic and extrinsic risk factors. Intrinsic risk factors include mostly anatomic and other variables that are innate to the individual, such as gender, age, height, weight, personality type (e.g., aggressive, passive), and anatomic factors such as femoral anteversion, genu varus or valgus, pes planus or cavus, bone density, muscular flexibility, and leg-length discrepancies. Extrinsic risk factors include training variables such as mileage, hill running, pace, interval training, equipment (shoes, shoe inserts), and training surfaces.

Patellofemoral pain syndrome is the most common overuse injury of the lower extremity, and is particularly prevalent in those who are physically active. For example, approximately 2.5 million runners will be diagnosed with PFPS in a given year. PFPS also is a significant problem in the military as it has been reported that 37% of recruits develop PFPS while in basic combat training. Females are reported to be at greater risks for PFPS than their male counterparts. Alarmingly, 70% to 90% of individuals with PFPS have recurrent or chronic pain, In addition, the result of a recent study suggest that having PFPS as a younger individual may predispose one to develop patellofemoral osteoarthritis later in life.