How Core Muscles Can Affect The Lower Extremity

Author(s): 
Brian Fullem, DPM

Occasionally, a podiatrist may encounter an athletic patient who does not improve with traditional treatment. We tend to focus on the injured area and may overlook weakness of the core muscles, which may contribute to foot or leg pain. The core muscles are extremely important in lower extremity muscle function.
The core muscles include the stomach muscles (the rectus abdominus, transverse abdominus, external and internal obliques and erector spinae) and the hip abductors (the gluteus medius and gluteus minimus).
If the core muscles are weak, particularly the gluteal muscles, then the pelvis will be unstable and this can lead to increased pronation of the lower extremity. The gluteus minimus and medius both primarily abduct the thigh.1 Weakness in the gluteals will have implications all the way down the kinetic chain. From heel contact to midstance phase, if the gluteals are weak, then the femur will adduct and internally rotate excessively. This leads to the knee falling into a more valgus position. The tibia will then excessively rotate internally relative to the foot. This leads to an increase in pronation.
The smaller muscles in the leg and foot are not strong enough to resist the pronatory force of the body’s weight during gait if the gluteals are not functioning properly.
There are a number of injuries that may not improve with traditional treatment if the hip abductors are weak. Plantar fasciitis, Achilles tendonitis, iliotibial band syndrome (ITBS) and medial tibial shin splints are all injuries that may be caused partly by weakness of the core group due to the increase of pronatory forces.
Runners are typically more prone to weakness of this muscle group due to a lack of lateral movement during their sport. In fact, Fredericson reported in 2005 that runners who participate during childhood and adolescence in sports such as soccer, baseball and basketball may develop greater and more symmetrically distributed bone mass, and have enhanced protection from future stress fractures.2

When Significant Hip Abduction Leads To Achilles Tendonitis
One patient, a runner in his 50s, presented at my practice with Achilles tendonitis. The patient had not missed a day of running for over 30 years and had an important marathon race that he had no intention of missing. His Achilles was swollen and painful, and he was running with an obvious limp. Despite my advice, the patient was unwilling to miss a day of running. He had tried many of the traditional Achilles tendinosis treatments including ice, stretching, massage and heel lifts.
However, one area that had been overlooked was his significant hip abductor and core weakness. Runners typically are only exercising their muscles in the same plane. In essence, they are only moving forward and, as a result, the core muscles may atrophy. These muscles are more challenged with lateral movements such as those that occur in soccer.
At that time, I worked with a physical therapist who thought a little bit outside the box. He found that improving my patient’s core weakness significantly reduced the stress on the Achilles. The patient was subsequently able to maintain his running streak and successfully completed his spring marathon.

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