“TRUNK” DRIVING: The Influence of the Thoracic Spine
Craig Faeth, PT, ATC, CSCS, FAFS
Have you ever been driving at night, or any time, and been behind another car swerving all over the road? You cautiously slow down, keep the car in front of you, and look for the best opportunity to pass safely.
Imagine that the thoracic spine is that car, only it isn’t swerving. The reverse is true. It is losing mobility as time passes. Subtly, your function is impaired due to this decreased mobility, and your body (your car on the road) begins to compensate. Instead of slowing down, your body begins to over utilize other joints and muscles to carry out the same function. The next door neighbors, the lumbar spine and lower cervical spine, suddenly have to pick up the slack and work a little harder. In response to this over recruitment of the lumbar spine, the hips (we’ll call them the police in this case) attempt to control traffic and isolate the problem. The isolation is often created through a decrease in hip and pelvic mobility which increases the demand on the lumbar spine. And so, a vicious cycle of compensation and motion loss begins all as a result of the thoracic spine deciding to lock itself up.
Clinically, this is a very common presentation. Whether a client’s dysfunction started with the thoracic spine or whether the thoracic spine lost motion as a compensation somewhere else in the body, is usually the challenge in assessment. In any event, the clinician will be rewarded with an improved outcome with their client by making sure to consider the influence of the thoracic spine on the kinetic chain.
Let’s consider the influence of a thoracic spine with limited sagittal plane extension, transverse plane rotation, and frontal plane side bending on the lower extremities in gait, with the right leg leading. As the pelvis is rotating to the left, trailing the right leg, normal gait would reveal the trunk rotating to the right with a helping arm swing of left shoulder flexion and right shoulder extension. A limitation in right trunk rotation and extension would decrease the total excursion of left hip extension, promoting a shortened hip flexor; simultaneously, the right hip fails to load properly in the transverse plane, promoting shortened internal rotators. As we have seen in gait, with the pelvis laterally flexing to the left during right foot loading, in order to maintain upright posture the lumbar spine side bends to the right. The thoracic spine must compensate by side bending to the left. A frontal plane limitation in side bending would necessitate a decreased hip adduction excursion on the right to reduce side bending stress to the thoracic spine. Over time, this compensation promotes stiffening of the IT band, gluteus medius, gluteus maximus, the powerful internal rotators, as well as the lateral abdominal wall.
Speaking of the abdominal wall, these thoracic spine limitations virtually guarantee poor abdominal loading which is so critical to lumbar stabilization. As Dr. Politis clearly illustrated in a previous newsletter, proper abdominal function demands threedimensional loading, or proprioceptive lengthening, prior to a concentric contraction. How does this loading occur? In gait, as noted above, anterior pelvic rotation lengthens the abdominals in the sagittal plane, left pelvic rotation lengthens the abdominals in the transverse plane, and left lateral flexion lengthens the abdominals in the frontal plane. Effective loading, however, is also dependent upon efficient three-dimensional motion of the thoracic spine and trunk. With limited thoracic extension, rotation, and side bending, the abdominals will not get the proper loading stimulus (neither will the spinal extensors), that is required for mobile stability of the lumbar spine.
The thoracic spine and trunk, or, as Gary Gray has referred to it, the three-dimensional cage, literally has the capacity to control lower extremity and lumbar function. In your understanding of chain reaction biomechanics and human function, it is important to appreciate the dramatic impact the thoracic spine has on the lumbar spine, which has a dramatic impact on pelvic motion, which has a dramatic impact on hip function, which directly influences knee function, which…you get the idea. These direct and indirect relationships are most keenly appreciated using Applied Functional Science principles, strategies, and techniques.
The trunk has the ability to drive human function for the better, as well as for the worse. May yours and your clients’ thoracic spines be mobile and well.