Farrokhi S, Pollard CD, Souza RB, Chen Y, Reischl S. Powers CM. Trunk Position Influences the Kinematics, Kinetics, and Muscle Activity of the Lead Lower Extremity During the Forward Lunge Exercise. J Orthop Sports Phys Ther 2008, 38: 403-409.

This study focused on lower extremity joint angles, joint impulse, and muscle activity during an anterior lunge. Trunk position was manipulated by reaching anterior towards the floor, or posterior overhead. Reaching forward increased the hip flexion of the lunging leg, increased the hip extensor impulse, and increased the muscle activity in the hip extensors (gluteus maximus and lateral hamstring). Reaching posterior decreased the hip extensor activity, decreased the hip extensor impulse, and increased the knee extensor impulse.

So why does the result of this study “matter for function”? The effect of reaching anterior at ankle or posterior at overhead provides a Strategy of “tweaking in” or “tweaking out” during training or rehabilitation. The PST Process of Applied Functional Science® at Gray Institute® dictates that Strategies must emanate from Principles (Truths) of human movement. The Principle that becomes important from this study is that when a muscle is lengthened, it is able to generate more force (and vice versa). This “truth” is in play in all three planes. The Strategy, based on this Principle, could be to start by adding in more muscle force from the hip, but then gradually reduce the contribution from the hip, shifting more responsibility to the muscles at the knee and ankle. The specific movements that make up the training / rehab program are chosen (and sequenced) consistent with the Strategy.

Let’s use an example of the PST Process applied to anterior knee pain in a runner. The runner wants a training program to prevent the recurrence of pain when running. An anterior lunge is a movement that is consistent with the landing phase of running, albeit with less stress. While performing the lunge, the client complains of some discomfort. Should this exercise be removed from the training program? The lunge movement probably can continue (pain-free) if more hip extensor muscle can be added to the lunge. Adding hip force will reduce the stress on the knee extensors. Based on the research study, this can be accomplished by reaching forward during the lunge. As the stress tolerance of the knee tissues improves, a logical progression would be to not reach as far forward. Over time, the progression would be to reduce the hip contribution by actually reaching backwards.

Applying the Strategy to the frontal and transverse planes is similarly logical. If the right knee is involved, then the hands would reach to the left in the frontal plane to add in force from the posterior-lateral hip muscles. In the transverse plane, the hands would rotate to the right. This creates internal rotation of the lunging hip. The internal rotation lengthens the posterior-lateral hip muscles, allowing them to generate more force. In both planes, the arms movements would gradually be reduced in magnitude. A comprehensive training program would eventually drive the arms in the opposite direction, transferring more of the responsibility to the knee musculature. This progression allows the knee tissues to get stronger in response to the increasing physiologic load created by the movement.

Understanding the PST Process and creating a “tweak in” to “tweak out” progression allows movement practitioners to take an exercise that hurts and use it to solve the problem. Dr. Gary Gray calls this “creating an environment for healing that transforms the cause into a causative cure.”