As the gait cycle progresses, the lead leg becomes the trail leg. But there may be an advantage to consider what is happening to the trail leg at the same time the lead leg is going through its REAL bone and RELATIVE joint motions. Since the previous blogs used the right leg as the lead leg, this blog we will focus on the left leg when discussing the trail leg. When the right foot strikes the ground, the three RELATIVE joint motions occurring in the trail / left hip are extension, abduction and (surprisingly) internal rotation. Knowing which REAL bone motions create the 3 RELATIVE joint motions is important because both propulsion off the trail leg and loading of the lead leg will be affected by trail hip dysfunction.
The abduction of the trail hip (left hip in this example) in the frontal plane is created by the REAL bone rotations of abduction of the femur and lateral flexion of the pelvis to the left towards the trail leg. The translation of the pelvis to the right (lead side) is also an important contributor to the RELATIVE abduction of the trailing left hip. This is the same REAL bone translation (slide) of the pelvis that helps create the RELATIVE adduction of the lead hip discussed in a previous blog. Also, it is important to recognize that the REAL abduction of the femur does not occur in the manner we usually think of. When the foot is not in contact with the ground, abduction occurs when the distal end of the femur moves away from the body. However, in gait when the trail foot is still on the ground, the slide of the pelvis to the lead side brings the proximal end of the femur away from the foot. When the proximal end slides to the right, REAL abduction of the trail femur is created. The RELATIVE abduction occurring at the left hip lengthens and activates the adductors muscles of the trail leg.
In 3DMAPS the Right Same Side Lateral Analysis Movement creates RELATIVE left hip abduction by replicating the frontal plane REAL bone motions of the pelvis and the femur that occur in the trail hip. The Mobility Movement indicates the available REAL bone and RELATIVE joint motions. The Stability Movement provides insight into the body’s control of those motions. Since the trail hip is directly connected to the lead hip by the pelvis, dysfunction in the lead hip and leg can negatively influence the REAL bone motions of the pelvis and the left femur. The Left Opposite Side Lateral Mobility and Stability Analysis Movements in 3DMAPS would give insight into this possibility.
Restrictions of pelvis motion will limit RELATIVE hip abduction of the trail leg. Both the lateral flexion to the left and the translation to the right provide contributions to the RELATIVE joint motion. When the pelvis laterally flexes to the left, this produces RELATIVE lateral flexion to the right of the lumbar spine above. Loss of lumbar right lateral flexion will influence the left hip abduction occurring in the trail leg. To determine if the lumbar spine could be restricting pelvis motion, there are two Movement Analysis Chains that use the arms to drive the spine into right lateral flexion. One is the Left Same Side Lateral Chain, and the other is the Right Opposite Side Lateral Chain.
The power of 3DMAPS is that in addition to documenting global movement dysfunction, specific impairments can be identified. Once the movement impairments are determined, a logical sequence of movements to eliminate the dysfunction can be designed by using the Performance System.