Overuse injuries among runners are common and several studies have reported that 50–60% of all runners will sustain a lower extremity injury each year. The reason why an injury occurs is difficult to determine but essentially results from a combination of clinical factors (i.e. muscle flexibility, muscle strength), biomechanical factors, and training errors. Core stability training is gaining popularity in the running community as more runners are made aware of how weakness in the “core” of the body can negatively influence lower extremity biomechanics and running performance. The lumbar, abdominal, pelvis and hip region together are considered to be the core of the body and optimal core function involves both mobility and stability. Proper core stability can help maximize running performance, maintain the center of gravity over the base of support, control lower extremity limb motion while running, and help prevent running injuries.

From a biomechanical perspective, hip muscle weakness can play a significant role in the development of running-related injuries. A recent study by Niemuth (2005) investigated a group of 30 runners with a variety of running injuries compared to runners with no injuries. Factors such as training, leg dominance, anatomical alignment, previous injuries, and hip muscle strength were analyzed to determine what factors play the greatest role in the development of running injuries. The results indicated that the injured runners demonstrated significantly weaker hip abductor (located on the outside of the hip) and hip flexor (located on the front of the hip) muscles compared to their non-injured limb and compared to the control group. A study from our lab (2006) looked at data from 364 runners with various running injuries and involved measurements of hip muscle strength and running biomechanics. Based on the biomechanical and clinical evaluation, a rehabilitation program was prescribed to improve hip strength. Surprisingly, 92% of the patients showed significant weakness of their stabilizing hip muscles. At the 4-week follow-up, 89% of the patients reported a 75% improvement in pain. A more recent from our lab (2008) had patients with patellofemoral pain syndrome (runner’s knee) perform only 2 hip abductor muscle strengthening exercises over a 3-week period of time. Baseline and post-rehabilitation measures of pain, muscle strength, and running biomechanics were measured to understand the role of this specific hip muscle group in controlling knee mechanics when running. Overall, the patients reported at least a 50% reduction in pain, a 40% improvement in strength, and significant improvements in their running mechanics was measured following the 3-week rehab protocol. These results suggest that the hip abductor muscles are critical for the rehabilitation of running-related injuries and improvements in strength can effectively resolve pain associated with running injuries. Surprisingly, these studies are the first to show an association between hip muscle strength and the development and rehabilitation of overuse running injuries.

Other studies have also suggested that hip strength is a primary contributing factor to the development of iliotibial band syndrome. Iliotibial band syndrome (ITBS) is the second leading cause of knee pain in runners and is the number one cause of pain on the outside of the knee. ITBS is an overuse running injury that results from repetitive friction of the IT band over the outside of the knee joint. One of the hip abductor muscles is located within the IT band and functions to reduce forces within this tissue during running. Some authors have suggested that weakness or inhibition of the hip abductor muscles leads to a decreased ability to stabilize the pelvis and adequately control lower limb alignment while running thus resulting in excessive forces sustained by the IT band.

Fredericson (2000) randomly selected 24 runners with ITBS and compared hip abductor strength to a control group of 30 non-injured runners. Similar to the findings of Niemuth (2005), these authors also reported that runners with ITBS exhibited significantly weaker hip abductor muscle strength in the affected limb compared to the non-injured limb and compared to the healthy runners. These authors also reported that following a 6-week hip abductor strengthening program, 22 of 24 ITBS patients demonstrated a 35% to 50% increase in abductor muscle strength and were free of ITBS pain while running. Therefore, this study is strong evidence that a relationship exists between hip abductor muscle weakness, side-to-side imbalances in strength, and the development and effective treatment of ITBS. While this study demonstrates a link between hip muscle strength and ITBS, there is only one study that has examined running biomechanics in runners with ITBS. We conducted a study (2008) that examined differences in running biomechanics between 35 runners who had previously sustained ITBS and 35 runners with no knee-related running injuries. Using a 3-dimensional camera system to measure joint angles, along with force plates to measure ground impact, knee and hip joint forces were calculated. The results indicated that the ITBS group exhibited a significantly greater peak hip and knee angles similar to a more “knock-kneed” running posture and significantly greater knee twisting forces compared to a group of healthy runners. Similar to the other investigations, these results strongly sugest that weakness of the hip abductor muscles result in changes in running biomechanics which may require greater passive restraint from the IT band while running and, over time, lead to ITBS. Therefore, adeqaute hip muscle strength, in paticular the hip abductors, is important to help prevent and rehabilitate from running injuries.

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