What constitutes the hip structure? I think of the hips as more of a region than an anatomical place on the body. However, to define the “hips” as an osseous structure, it would consist of the interplay between the head of the femur with the acetabulum of the pelvis, along with its surrounding joint capsule and ligaments that support this synovial ball and socket joint. It is essential to understand that the head of the femur is oriented with the acetabulum in three planes, and for this reason, the hip is a major transmitter of rotational forces from top to bottom, and vice versa. We must keep in mind, however, that the meeting of these structures is part of a larger picture, because what happens distally affects proximally (just as what happens on one side of the body affects the other). The muscles attaching the pelvis to the femur are some of the strongest and most powerful of the body and include the deep rotators of the hip, the adductors, rectus femoris, hamstrings and gluteus complex, consisting of the glut maximus, medius, minimus and the TFL. If observed together, these muscles angle in just about every direction, with none being purely horizontal or vertical. If looked at in an integrated fashion, with the idea that muscles work together to transmit and utilize energy efficiently, we begin to grasp how dominant the rotational forces are that affect the body and how important it becomes to train the body to handle these rotational forces.
Traditionally, we have thought of muscle and muscle function in an isolated manner and described it as if the body were lifeless on a table. Perhaps this is because in the 18th and 19th centuries, when Man was learning about the body by dissecting cadavers (likely stolen), experiments were performed in an effort to discover the function of the muscle and bone. The beginning and ends of a muscle were hooked up to electrodes (i.e,. the hamstrings) and turned on, resulting in muscle shortening (knee flexion). This description is the one primarily taught in anatomy books and is an isolated interpretation of muscle action. What is not taken into consideration is the way in which gravity and ground reaction, which is the force exerted on the body by the ground, affect the body. With the infusion of gravity and ground reaction that lengthen fascially connected structures, suddenly muscles don’t act upon the body to generate a movement (i.e., hamstrings performing knee flexion). Instead, the muscle responds to forces presented upon it by lengthening of muscle and energy absorption, such as the quads slowing knee flexion or hamstrings slowing hip flexion and knee extension. With this paradigm of thought, “stretching and strengthening” become synonymous, as strength becomes the body’s ability to lengthen, transfer and utilize energy with control and efficiency. To understand that muscles work together in an integrated fashion, battling gravity and ground reaction to keep upright and moving is an important step in our understanding of human motion.
This last point is critical to the understanding of movement, biomechanics and “function.” Muscles must first decelerate motion in all three planes (also described as absorbing energy, eccentrically loading, pronating or lengthening) before accelerating (also described as utilizing energy, concentrically lengthening, supinating or exploding). If looked at traditionally, then the gluteus complex either extends and/or abducts the hip, which in isolation is true. However, in this interpretation, it describes the muscle as first shortened before lengthening. Yet if looked at in integration, the role of the gluteus complex becomes far more complicated. We begin to understand that the gluteus complex has many different jobs, depending on where the femur is in relation to the pelvis. To better understand the role of the glut complex in relation to the hip, an understanding of its action in gait is necessary.
During the swing phase of the right leg and until heel strike, the right glut complex works to decelerate hip flexion in the sagittal plane, adduction in the frontal plane and internal rotation (IR) in the transverse plane. It is important to recognize that the right glut complex slows adduction/IR of the right swinging leg, because at toe off, the right “hip” is relatively abducted and externally rotated on the femur, which means that during swing, the femur is going to adduct and internally rotate on the pelvis. From heel strike of the right foot until midstance, the right glut complex slows the pelvis on the femur adduction and IR. For example, as the left leg is swinging, the right glut complex is stabilizing the hip in the frontal plane by controlling the left pelvis dropping inferiorly (pelvic on femoral adduction) in the transverse plane by slowing IR as the pelvis migrates forward over the femur. Once at midstance, the glut complex (along with other muscles including the opposite quadratus lumborum) assists to stabilize the lumbo-pelvic complex. It is extremely important to discern that the glut complex’s integrated function has little to do with hip extension in gait. Hip extension in gait is primarily accomplished from the body’s momentum of traveling forward over the foot and its reaction to gravity and ground reaction. During the propulsive phase of gait, the glut complex externally rotates the hip and propels the body forward, in conjunction with the calf.
In order to fully incorporate the way in which we look at, train and rehabilitate the body, being cognizant of the relationships that exist between structures is essential. If we can understand that structure feeds function, then we can begin to enhance the ability of one part by creating a chain reaction to indirectly affect the other. For example, in function if one demonstrates decreased hip extension, he will often demonstrate decreased dorsiflexion and often ipsilateral shoulder flexion, unless compensated for somewhere else in the kinetic chain (such as the lumbar spine). The hip flexors, what Physical Therapist Gary Gray calls the front butt, are eccentrically loaded (slowing hip extension) while the plantar flexors slow dorsiflexion. In other terms, when the hip is extending, if looked at from the ground up with the eccentric load first, the calf is also slowing hip extension because the soleus is slowing the tibia moving anterior over the talus, allowing the femur to move faster and further anterior than the tibia. Also, based on the proximal attachment points of the gastrocnemius (the posterior femoral condyles), when eccentrically loaded it assists to achieve full knee extension by slowing the femur moving over the tibia and pulling the distal end of the femur into a relatively posterior position on the tibia, which arthrokinematically is what happens between the femur and tibia during knee extension. This action further extends the hip by allowing the pelvis to continue to move forward faster than the femur.
As we can see, the body is an amazingly complicated machine. When we study movement, there are obvious relationships that become apparent. However, there are even more relationships that only make themselves known when we continue to study, watch and think about motion, muscle function and the body in general. This understanding allows us to further serve our patients/clients, which is the essential element. In further discussions, we will take a look at more of these relationships of human motion, as well as demonstrate different ways in which to train in an integrated fashion, utilizing gravity, ground reaction and creativity.