Understanding the motion of individual joints during functional activities is essential for training, rehabilitation, and injury prevention. At Gray Institute, this knowledge is called Chain Reaction® Biomechanics (CRB). The CRB of joint motion is specific to the activity, and requires knowledge of the bone segment motions in each of the three planes.
This blog will discuss internal rotation of the hip joints during the activity of walking. When the leading leg loads during the process of weight acceptance, the hip joint goes through internal rotation in the transverse plane. As the trail leg loads for propulsion, that hip also experiences internal rotation. However, while the joint motion is the same, there is a critical difference between the actual bone motions that create the internal rotation.
If we use an example where the right leg is the lead leg (left leg is the trail leg), the distinction between the CRB for each hip becomes clear. When the lead leg contacts the surface, the ground reaction force acting on the lateral heel causes the calcaneus to evert and the subtalar joint pronates. Because of the angle of the subtalar joint axis, the lower leg will internally rotate. The chain reaction continues up the extremity, and the femur will internally rotate and the pelvis will rotate to the left in the transverse plane. Since internal rotation of the right femur is equivalent to rotating to the left, the pelvis and the femur are rotating in the same direction. Because the chain reaction is being driven from the ground (bottom-up), in normal circumstances the femur will rotate slightly faster and further than the pelvis.. This relative difference between the femur and the pelvis creates internal rotation at the right hip joint.
In the trail leg (left) the subtalar joint is supinating. The lower leg and femur are externally rotating in the transverse plane. The challenge here is to “see” how the femur can be externally rotating while the motion at the hip joint is internal rotation. Remember that the legs are connected by the pelvis, and the pelvis is rotating to the left as the right leg swings forward even before ground contact. In fact, the rotation of the pelvis drives the femur and lower leg into external rotation that assists the supination of the subtalar joint. In contrast to the lead leg, this chain reaction is driven from the top-down. If we dig deeper into the bone motion, the pelvis is rotating to the left and the left femur is rotating to the left (externally rotating). It seems logical to think that if the femur is externally rotating then the hip joint must be externally rotating. But since this is a top-down chain reaction the pelvis should be rotating faster and further than the femur. This produces relative internal rotation of the left (trail) hip joint. The real bone motion is external, but the relative joint motion is internal rotation.
When designing training, rehabilitation, and injury prevention programs it matters how the internal rotation is created. At Gray Institute, our goal is to create movements that are authentic (consistent) with the specific functional activity. This allows the proprioceptors to activate the muscles in the correct combination and proper sequence to effectively and efficiently complete the task. These muscle synergies are specific to the beginning position of the body, the external and internal forces driving the movement, and actual movement to be executed.
To learn more about Chain Reaction® Biomechanics, please visit the Gray Institute website: www.grayinstitute.com.
To be able to assess your clients with both top-down and bottom-up Chain Reaction® Movements consider the 3DMAPS® (3D Movement Analysis and Performance System) certification.
To learn now to progress your programs based on your client’s present level of success, please consider enrolling in CAFS (Certification in Applied Functional Science®).