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.
During gait, the RELATIVE hip joint motions of the lead and trail legs are opposite in the sagittal and frontal planes. In the sagittal plane, the lead hip flexion loads the posterior-lateral hip muscles while the trail hip extension loads the anterior-medial hip muscles. Similarly, in the frontal plane, the lead hip adduction loads the posterior-lateral hip muscles, while the trail hip abduction loads the anterior-medial hip muscles. However, the “opposite” RELATIVE hip motions are not part of the Chain Reaction Biomechanics of gait in the transverse plane.
For many functional activities, the transverse plane is the “power” plane, while the posterior lateral hip (back butt) is the power source. During gait, the truth of the Chain Reaction Biomechanics is that both hips load the posterior lateral hip muscles with RELATIVE joint internal rotation. The REAL bone motions that create the RELATIVE internal rotation are very different for each hip. When the lead/right foot contacts the ground, the Chain Reaction (described in a previous blog) causes the right femur to internally rotate in the transverse plane. The pelvis rotates in the same direction (left) as the right femur, but the femur moves faster. Both bones are moving in the same direction, but the because the femur moves faster, the resulting RELATIVE hip motion is internal rotation. At the same time, the trail/left femur REAL bone motion is external rotation. We would expect the RELATIVE joint motion to be external rotation, but because the pelvis is rotating in the same direction faster than the left femur, the REALTIVE joint motion is internal rotation! The posterior lateral muscles of both hips are loaded in the transverse plane.
Understanding how REALTIVE hip internal rotation occurs in the lead leg compared to the trail leg highlights the limitations of checking hip rotation on a table. Being able to replicate the REAL bone motions of the pelvis and both femurs simultaneously as they occur in gait is a powerful assessment tool. Using just the lunge component of 3DMAPS, the REAL bone motions in the transverse plane can be replicated. Sticking with our example of right/lead and left/trail, a right leg opposite side rotational lunge in 3DMAPS will cause the right femur to internally rotate to the left faster than the pelvis is rotating left, creating RELATIVE right hip internal rotation. At the same time, the left rotation of the pelvis will occur faster than the external (left) rotation of the trail leg femur, creating left hip internal rotation.
The power of replicating the authentic REAL bones motions for both the lead and trail hips can’t be overstated. The power of 3DMAPS is the ability to determine the Mobility and Stability of movements that match whatever activity our clients engage in.