How Core Muscles Can Affect the Lower Extremity

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.

What The Research Reveals

Fredericson has published several significant articles proving the association between weakness in the hip abductors and running injuries. One study compared a group of 24 runners with ITBS to a control group of 30 healthy runners.3 The injured group had significantly weaker hip abductors. After six weeks of strengthening of the core muscles primarily through eccentric exercises, 22 of the 24 runners in the injured group were back to full activity. Traditional treatment of ITBS had focused on stretching but with Fredericson’s work, the focus should now shift to strengthening.
In another study of recreational runners, researchers compared 30 runners with injuries to 30 randomly chosen healthy runners.4 The runners had various injuries throughout the whole leg and there was a statistically significant difference in hip abductor strength in the injured runners’ affected limb versus the healthy side. The uninjured runners did not have any difference in hip abductor strength. A third study showed a correlation between patellofemoral pain and hip abductor weakness.5 Thirteen athletes with unilateral patellofemoral pain underwent examination and a significant difference was present in hip abductor strength in comparison to the healthy limb.

Key Diagnostic Tests For Hip Abduction
In order to examine the strength of the hip abductors, one should start with non-weightbearing testing. Test patients on their side with the leg raised up laterally. Make sure they rotate their hips forward on the side that is not on the table. This will eliminate the influence of other muscles such as the quadriceps. Have the patient resist while you push down the leg.
Another test is checking for a Trendelenberg sign on the examination table. Have the patient bridge up off a flat table with the feet flat. The patient should then fully extend one leg out with the knee locked. If the hip drops on the side of the extended leg, that is a sign that the opposite hip abductors are weak. Physicians can also look for a Trendelenberg sign during the gait examination.

A Guide To Core Strengthening Exercises
All of the recent studies point toward the addition of hip abductor and core strengthening as being beneficial for the training of distance runners.
In regard to strengthening of the core muscles, there is an excellent guide at https://www.coachr.org/core_stabilisation_training_for.htm. Fredericson has developed this program specifically for runners to help prevent injuries. The plan includes the use of dynamic exercises, including the use of a stabilization ball, rocker board, medicine ball, lunges and step-ups. Injured runners can begin simply with side leg lifts.
I recommend people lie on their side and slide the leg up a wall with the back of the leg against the wall and the foot pointed down. Start with one set of 20 on each side and progress to three sets of 20 per day.
I also begin people on bridging up exercises, and side and front planks. One can find another excellent core program at smiweb.org.

In Conclusion
Indeed, weakened core muscles can lead to increased pronation and subsequent lower extremity pain. Podiatric physicians should consider this possibility if athletes do not respond to conventional treatments for conditions such as plantar fasciitis and Achilles tendonitis.
There are simple tests one can perform to detect hip abduction. If core muscles are contributing to lower extremity ailments, one may need to consider the possibility of a physical therapy referral.

Dr. Fullem is a Fellow of the American College of Foot and Ankle Surgeons, and the American Academy of Podiatric Sports Medicine. He is board-certified in foot and ankle surgery by the American Board of Podiatric Surgery. Dr. Fullem is in private practice in Newtown, Ct.

Dr. Richie is an Adjunct Associate Professor in the Department of Applied Biomechanics at the California School of Podiatric Medicine at Samuel Merritt College. He is a Past President of the American Academy of Podiatric Sports Medicine.

References:

1. Beck M, Sledge JB, Gautier E, Dora CF, Ganz R. The anatomy and function of the gluteus minimus muscle. J Bone Joint Surg, 82-B: 358-363, Apr 2000.
2. Fredericson M, Ngo J, Cobb K. Effects of Ball Sports on Future Risk of Stress Fracture in Runners. Clin J Sport Med. 2005; 15: 3: 136-141.
3. Fredericson M, Cookingham CL, Chaudhari AM, Dowdell BC, Oestreicher N, Sahrmann SA. Hip abductor weakness in distance runners with iliotibial band syndrome. Clin J Sport Med 2000; 3 (10): 169-75.
4. Niemuth PE, Johnson RJ, Myers MJ, Thieman TJ. Hip muscle weakness and overuse injuries in recreational runners. Clin J Sport Med. 2005 Jan;15(1):14-21.
5. Cichanowski HR, Schmitt JS, Johnson RJ, Niemuth PE. Hip strength in collegiate female athletes with patellofemoral pain. Med Sci Sports Exerc. 2007 Aug;39(8):1227-32.