PT on the Net Research

Stabilization of the Knee

Even as our knowledge of the human body increases, so too does the incidence of chronic, movement related problems such as back and knee pain. It is clear that the majority of chronic pain arises due to a combination of factors including poor posture, muscle imbalance, under use and over use. In the majority of people, faulty movement (i.e., over use, poor movement quality/technique or sedentary behavior) has often resulted in muscle weakness in key areas, causing compensatory muscle tightness, which is at the root cause of their problems. My belief is that through functional exercise, we can restore muscle function, improve human movement and reduce the incidence of chronic pain.

Functional exercises reproduce and therefore improve everyday movements. To accurately reproduce movement and design a functional program, we have to understand how the body works, what movements we commonly perform and how the body goes about performing these movements. Exercises can then be adapted to encourage correct muscle function, improve muscle balance and restore good movement. In many cases, this is enough to reduce chronic pain. This article explores how muscles work during functional movement. I will relate this specifically to the gluteus maximus (GM) and look at how it contributes to functional movements such as running and lifting. Key to this discussion is how GM interacts with other muscles and connective tissue, in particular the latissimus dorsi (LD) during these functional movements. First, let's look at how muscles work "synergistically" to produce movement.

Muscles never work in isolation to produce movement or to stabilize joints. Some instructors still talk about isolation exercises, exercises that isolate individual muscles. The body never uses muscles in isolation. There are always a myriad of muscles contributing to create any movement. This is called muscular synergy.

Isolation exercises are those that allow movement at only one joint or involve one prime mover (e.g., bicep curl). Compound exercises involve movement at more than one joint or with more than one prime mover (e.g., squat).

There is often a main muscle responsible for producing force, the prime mover or agonist. There are also other muscles that contribute to force production in the same direction, known as synergists. How well we co-ordinate synergistic muscle action affects our level of force production during a movement. There are also many more muscles that position the moving joints so that the forces we produce translate into movement in the direction we want, called neutralizers. Without neutralizing muscle action, movements would be inaccurate and would lack force. Many more muscles stabilize other joints so that postural alignment can be correctly maintained, and we have a solid base from which to move. These muscles are known as stabilizers. Reading about core stabilization helps you to understand that if proximal joints (e.g., the spine) are not stable, this affects our ability to produce force at distal joints. Force production, even for the most simple of movements, therefore relies on the synergy of many different muscles working together, acting throughout the body. The degree by which we produce forceful, accurate movements is dictated by how well we co-ordinate these different muscles within the context of that particular movement. Functional exercises therefore strengthen movements not muscles.

Muscles also work very differently to how we read in conventional texts. Each muscle involved in a movement will have a different function, depending on the type of movement we do, the position we start in and the speed and force with which the movement is performed. The GM is a classic example of a muscle that has a much greater function than described by most texts; it works with many other muscles and connective tissue to allow movement. While the GM is classically known to concentrically extend the hip, it has far more to do than just this.

Firstly, we have to appreciate that hip extension is assisted not only by the hamstrings but also adductor magnus and posterior fibres of glute minimus and medius. The GM is therefore especially important in extending the hip under conditions of knee flexion, when the hamstrings are at a mechanical disadvantage (i.e., climbing stairs). The GM also laterally rotates the femur at the hip. Different fibres contribute to both hip adduction and abduction, and GM posterior tilts the pelvis on the thigh when the leg is fixed, thereby directly assisting trunk extension. These movements are also assisted by a vast number of other synergists, stabilizers and fixators.

We know that in real function, force has to be eccentrically controlled and isometrically stabilized before movement can be concentrically produced. Failure to adequately absorb load results in loss of stabilization and injury. In functional movements such as gait (running), the GM together with posterior fibres of glute medius and minimus, eccentrically controls pronation (a combination of internal rotation, flexion and adduction) at the hip and knee. This is why the GM can be so sore the day after doing a heavy lunge workout. This important functional role is very rarely explained in conventional texts. From this, we see that GM has a varied role to play in functional movement. If we are to truly understand GM function, we have to understand about key synergistic relationships that GM has with other muscles and structures of the body, in particular fascia and connective tissue.

The GM has an important role to play in stabilizing key load bearing structures of the body. When we run or lift heavy loads, as is common in daily life, key structures have to absorb massive loads. These structures include the knees, SI joints and spine. Most of the weight of the body rests on these structures, and they are a key area for chronic pain and injury.

Via its attachments to connective tissue and fascia, the GM plays a very important role in stabilizing key load bearing structures such as the knee, SI joint and lumbar spine. I now want to look more closely at the synergistic relationship the GM has with the LD to demonstrate how muscles never truly work in isolation.

There is a key relationship between the GM and the contralateral (opposite side) LD. These two powerful muscles are linked via the TLF. When the contralateral LD contracts, force is transmitted through the TLF creating additional tension, stretch and increased force production in the opposite side GM. If the contralateral LD contracts in unison with the GM, greater force is produced in the GM.

If we equate LD contraction with increased GM force production, we can theorize that through co-contraction with the GM, the LD aids stabilization of the knee, SI joint and spine. We can see this in action during functional movements. During running, we see that our contralateral arm drive activates the LD as we extend the arm. This happens at the same time as we heel strike and begin hip extension, which involves GM contraction. When we pick up a weight, both LD contract as we stabilize our shoulder girdle. At the same time, our GM contracts as we extend the hip. Due to its relationship with GM via the TLF, our LD may contribute towards hip extension and stabilization during functional movements such as running and lifting.

So how does this influence our own training? In functional training, we try to promote the natural synergies of the body to achieve optimal function and balance. To achieve this, we should use functional movement patterns relevant to every day movement. I often encourage my clients to deadlift as well as squat larger loads. The deadlift encourages this synergistic relationship between the GM and the LD. As clients engage their GM by extending through the hips, they co-contract LD by picking up a weight. The contralateral LD activation will encourage GM involvement by stabilizing its proximal attachments to the TLF. This will be reflected in improved lower back, SI joint and knee stability. How often do we walk around with heavy weights on our back? rarely. How often do we have to lift heavy weights? Often. The body is designed to lift weights from the ground. To do so encourages natural muscle synergy. Running, stepping and lifting exercises such as the deadlift and lunge are examples of key exercises for the healthy, functional individual because they reproduce the tasks we perform in everyday life and promote the synergistic relationship between the GM and the contralateral LD.

For a variety of reasons (faulty movement, overuse, sedentary behavior, injury etc), there are times when these muscle synergies are disturbed. Weakness can develop in one or several muscles in these chains. In conditions in which one muscle develops weakness, invariably the other muscles in these chains have to compensate and work harder to create adequate movement and joint stability. Because this is not a natural situation, this type of muscular substitution causes alterations in posture, faulty movement, loss of performance, stress and eventual pain or injury. One term used to describe this is synergistic dominance.

Some muscles are prone to developing weakness if they are overworked or placed in conditions of excess stress (note that injury or lack of use may also be deemed conditions of excess stress). GM is an example of a muscle prone to lengthening and weakening under conditions of excess stress. Postural repercussions of a weakened GM might include over pronation (flexion, adduction and internal rotation) through the hip and knee, anterior tilt of the pelvis, excessive extension of the spine and scoliosis if the weakness is associated with just one side. The hips would appear wider, with the greater trochanter protruding because of the influence on the pelvis.

With weak GM, your client becomes prone to back pain, SI joint instability and knee pain. Synergistic muscles become overworked and hypertonic, such as the other main extensor muscles, the erector spinae and hamstrings. We might also speculate that muscles such as iliopsoas and quadratus lumborum are prone to tightness due to overwork as they attempt to stabilize the lumbar spine. Biceps femoris also tightens to help stabilize the SI joint via its attachment to the sacrotuberous ligaments. All these are symptomatic of an under active GM and common in people with a hyperlordotic or sway back posture, resulting from too much time sitting for example. For these clients, we have to reactivate the GM and build its synergistic relationship with the LD, so that it can start fulfilling its role in stabilizing the SI joint, back and knee. If the body is under using the GM during these exercises, we have to create functional movements that promote correct muscular synergy.

This muscle synergy occurs on a completely subconscious level. As Paul Chek says, "The brain knows nothing of muscles, only movements." We can consciously contract our GM in simple isolation (single joint) exercises such as a prone hip extension, but we cannot consciously alter muscle synergy during more functional movements such as gait, lifting or landing from a jump. This is especially so when the GM is inhibited, weak and the body is preferentially recruiting other muscles, such as those highlighted above.

In a functional exercise, we have to manipulate body position to create nervous and mechanical advantage for the muscles we want to preferentially strengthen. The nervous system activates muscles in response to neural stimuli such as stretch, load, ground reaction force, gravity and momentum. Proprioceptors recognize changes in the environment, providing the brain with information. At this point, the nervous system reflexively activates muscles to achieve stabilization and balance. Whenever we place a muscle under a loaded stretch, we up regulate the nervous system, encouraging force production. We can also encourage the synergistic relationship between the GM and the LD by creating exercises that cause the two to contract at the same time.

The exercises below attempt to increase force production in the GM by placing it under a condition of loaded stretch. We also encourage natural muscle synergy by activating the contralateral LD. Your clients performing these exercises should feel a reduced tendency to pronate through the knee and foot when doing these exercises, with their weight shifting to the outside of the foot on the loaded leg(s). They should feel an increased sense of stability through the lower back. They should feel powerful muscular work, particularly in the GM.

Lunge with Reach Across 1 Leg Squat with Reach Across
1 Arm Split Stance Deadlift Split Stance Dumbbell Row
1 Arm Cable Pullover

There are many other muscles synergies that we know exist throughout the body and probably many we do not know about. The key to functional exercise is to encourage correct muscle synergy to promote correct muscle function and balance. In this way, I believe we can start to combat movement related chronic pain.


  1. Chaitow L., J. Delany. (2002) Clinical application of neuromuscular technique, volume 2; the lower body. Churchill Livingstone.
  2. Chek, P. (1993). Scientific Back Training; Correspondence course.
  3. Chek, P., (2004). Scientific Balance Training - Parts 1-6
  4. Clark, M. (2002) Essentials of Integrated Training - Part 8
  5. Clark MA. Integrated Training for the New Millennium. Thousand Oaks, CA: National Academy of Sports Medicine; 2001
  6. Dalcourt, M. Momentum in Training: Friend or Foe?
  7. Janda, V. (1986). Muscle weakness and inhibition (pseudoparesis) in back pain syndromes. IN Grieve, G. (ed) Modern manual therapy in the vertebral column. Churchill Livingstone, Edinburgh.
  8. Vleming, A. V. Mooney, T. Dorman, C. Snijders, R. Stoekart (1999). Movement, stability and lower back pain. Churchill Livinstone.