The importance of your butt!

by | Nov 21, 2015

We have previously discussed how important hip extension is to the runner, and that it should primarily be produced by the gluteus maximus muscle. So, why am I writing another article about the importance of the butt?! Haven’t we already shown this?

The gluteus maximus is one of three gluteal/butt muscles. We also have the gluteus medius and minimus, which are certainly not idle muscles. Today we will consider the importance of gluteus medius and you will see why the butt is so very important to runners! As with the gluteus maximus article, I will then follow up with some posts on the best exercises for it.

Let’s take a quick look at the anatomy of gluteus maximus and medius:

The Gluteus maximus and medius muscles

We can see in the above images that maximus is more superficial and covers a larger area. We can also see that some of the muscle fibers are directed in a similar direction which suggests there is some overlap of function. This is true, as we see that they both produce hip extension and external rotation (see this video for a recap on different hip movements).  However, gluteus medius is the most important muscle for hip abduction wheras gluteus maximus has minimal impact.

To understand how the glut maximus and medius muscles work over the three cardinal planes of movement, expand the tabs below. (Go on you engineers, you know you want to!)

Hip extension - sagittal muscle forces

This diagram represents the hip from the side. You can see a vertical dotted line going down through a red dot representing the center of motion for the joint in this plane. The movements of  flexion and extension occur about this center of motion and are represented by left and right directional arrows.  The other arrows mark the direction of force of the muscle. The start of those arrows represents where the force originates (i.e. where the muscle originates) and the end/arrowpoint where the force goes to (i.e. where the muscle inserts). The longer lines are longer muscles and can generate larger forces.  As you can see the posterior fibers of gluteus medius extend the hip. However the line of force for gluteus medius is closer to the center of motion and more vertical than that of glut maximus so it has less ability to extend the hip.

Hip extensors sagittal view

Adapted from: Neumann DA. Kinesiology of the Musculoskeletal System, Foundations for Physical Rehabilitation. Mosby Incorporated; 2002.

Hip rotation - transverse muscle forces

This diagram represents a right hip from above. The dotted line runs from anterior to posterior and runs through a red dot representing the center of motion for the joint in this plane. The movements of external and internal rotation occur about this center of motion and are represented by each of the left directional arrows.  The other arrows represent direction and force as per the previous diagram. We can see in this diagram that the gluteus maximus produces more external rotation than that of the posterior fibers of gluteus medius. We can also see that the anterior fibers of gluteus medius produce internal rotation. Therefore the gluteus medius actually can produce two opposing motions.

Hip rotators transverse view

Adapted from: Neumann DA. Kinesiology of the Musculoskeletal System, Foundations for Physical Rehabilitation. Mosby Incorporated; 2002.

Hip abduction - frontal muscle forces

This diagram represents a right hip from behind. The dotted line runs vertically and runs through a red dot representing the center of motion for the joint in this plane. The movements of abduction and adduction occur about this center of motion and are represented by the the right and left directional arrows.  The other arrows represent direction and force as per the previous diagram. We can see in this diagram that the gluteus maximus line of force runs directly through the center of mass so it produces minimal hip abduction. This compares with the line of gluteus medius whose force runs distant from the center of mass and therefore produces an abduction force.

hip abductors frontal view

Adapted from: Neumann DA. Kinesiology of the Musculoskeletal System, Foundations for Physical Rehabilitation. Mosby Incorporated; 2002.

Why is the gluteus medius muscle important? It produces external rotation and abduction which are not forward movements; so why are these movements important for runners?

When you run, you always are in a period of single leg stance, which means you never have both feet on the ground at the same time. When you are on one leg, you need the leg to stay upright, and the pelvis and trunk to stay level. When this is the case, the force from the ground (as it does with walking) comes up from the foot just medial to the knee (a). This creates a small varus/bow legged force. If we have abductor weakness, the femur/thigh bone falls into adduction and the pelvis drops to the opposite side. When this occurs we see and even greater varus force (b). This creates increase stress on the lateral collateral ligament of the knee, the Illiotibial Band (ITB), as well as the inside/medial side of the knee joint. To correct this, runners and athletes will often elevate the opposite side of the pelvis and lean towards the involved limb moving the ground reaction force more under the hip which reduces demand on the weak hip abductors. This creates a valgus/knock-kneed force, and even deformity (c). This tends to be amplifies by an increase in internal rotation due to weakness of the external rotators (glut max and med, and others). This places strain on the lateral joint, the ACL, and the medial collateral ligament of the knee.

Diagram showing what occurs at the pelvis, hip and knee when the gluteus medius and other abductors are weak

This diagram shows a) normal lower extremity (LE) position when standing on one leg. It shows increased hip adduction due to weak hip abductors (b). It shows compensation leading to a valgus deformity and force (c). Adapted from: Powers CM. The influence of abnormal hip mechanics on knee injury: a biomechanical perspective. J Orthop Sports Phys Ther. 2010;40(2):42-51.

We can see that the weakness in the hip abductors places stress on specific structures in and around the hip and knee. However, this weakness and these biomechanical changes have wider felt affect. What we tend to see in runners and athletes is that their initial contact is in a good position when looking from behind, but then because of hip abductor weakness they fall into either this wide varus (b), or valgus position (c). “Fall” is a great description because it signifies that an increased vertical displacement is occurring. This means that rather than moving energy forward, which we want to do to run efficiently and quickly, we are instead losing energy moving up and down. This also means that the already mentioned structures, as well as others such as the Achilles tendon, tibialis posterior, patella tendon, are all having to deal with increased loading.

Runner hip adduction

An example of hip adduction and opposite pelvis drop in a female runner.

An example of hip adduction and knee valgus in a female runner.

An example of hip adduction and knee valgus in a female runner.

So to summarize, hip abduction can either lead to a varus/bow-legged, or a valgus/knock-kneed gait pattern. This can stress and increase the risk of injury in certain structures. This risk is compounded by the additional vertical loading. Running efficiency and therefore speed is affected.

Can changes be made?

To some degree, this is going to be dependent upon how long you have faced these issues. Someone who is 50+ and has a valgus gait may have had it long enough that the joint itself has worn and there is actually irreversible structural change. They may be able to change the mechanics a bit, but not as much as a 20 or 40 year old who does not have a structural change. With the correct exercises, technique changes, and time, the 20 or 40 year old could make meaningful changes.

What are the correct exercises?

There may be several exercises that will be important. It is my experience that these hip abduction weaknesses do not tend to come alone. They tend to occur with glut max weakness, as well as trunk weakness. They also tend to occur with other muscles such as hamstrings being tight or over-dominant. The next two or three posts will identify the best exercises to access glut medius like we did with our recent glut max series. It is key to realize that in of themselves these exercises might not have the effect you need which is where seeing a trained professional can be helpful.

What technique changes can I make?

When it comes to technique there are multiple possibilities for change, and it is beyond the scope of this article to go through them. A good running coach such as our friends at Running Lane, or a video running analysis such as we offer can be helpful in delineating what the best changes are.

What is the correct amount of time?

We know that if we progress something too quickly, our risk of injury increases because the tissues (bone, muscles, tendon) do not have the time to acclimatize. It is often recommended not to increase parameters such as cadence, distance, speed by more than 10% a week. Exercise progression can be a little more challenging. I progress exercises based on how well a client can do them with respect to any pain they have. We are often poor judges of our own form which is why having an external person judging is important. A great example of this is how I recently did the video for the plank with bent knee hip extension – the first shot I did of this felt great with respect to form, but when I looked at the camera I was in shock as my butt was up in the air! Likewise, elite sportsmen do not always have good awareness of their body’s position and seek out professional help to produce the best possible form and performance.

Conclusion:

Avoiding excessive hip adduction and internal rotation is as important as achieving hip extension. The good news is, these issues are addressable. Follow the next two to three posts as I present the best gluteus medius exercises.

References:

  • Powers CM. The influence of abnormal hip mechanics on knee injury: a biomechanical perspective. J Orthop Sports Phys Ther. 2010;40(2):42-51.
  • Neumann DA. Kinesiology of the Musculoskeletal System, Foundations for Physical Rehabilitation. Mosby Incorporated; 2002.

Photo credits: Peter Mooney / Foter.com / CC BY

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