Why I’m a Big Fan of the ‘What’s That Strap’

Let me start by saying that I have no conflict of interest with the ‘What’s That Strap’; I’m just a big fan of the product. The human body does not move in one plane. Human movement occurs in all three planes all the time, and the ‘What’s That Strap’ allows us to train in all three planes simultaneously.

The gait cycle is a great example of this concept. Walking requires us to balance on one foot while maintaining our momentum created by the forward and rotational forces of gait. While this sounds simple, there is a lot that goes into helping us perform this seeming easy task. In previous blogs, I have discussed how the gait cycle can be broken down into two distinct phases (check them out here and here). Heel strike and foot flat are considered the absorption phase. During absorption, the ankle dorsiflexes, knee flexes, hip flexes, and thorax rotates to the ipsilateral side. This is also referred to as a flexion-rotation pattern as we observe a flexion theme in the lower extremity segments as the absorption phase occurs. Absorption gives way to propulsion, which consists of the heel off and toe off phases of gait. During this phase, the opposite occurs; the ankle plantarflexes, the knee extends, the hip extends, and the thorax rotates contralaterally. This is also referred to as extension-rotation patterning, as we observe extension occurring throughout the body during this phase. During human locomotion, we alternate between flexion-rotation and extension-rotation in a reciprocating fashion in order to get from one place to another.

In physical therapy school, we memorized muscle charts that showed muscles contracting either concentrically, eccentrically, or isometrically during each phase of the gait cycle. This isn’t quite how the body works though. You see, it costs us energy to stay upright and maintain our forward momentum, and if we relied solely on the concentric and eccentric contractions of muscle fibers during locomotion, it would come at a high metabolic cost. This would require our body to constantly bind and unbind the actin and myosin filaments of the muscles with each step we take. Lucky for us, our fascia and unique design helps us to minimize energy expenditure as we navigate from one location to another.

What is Fascia?

Fascia is a fibrous net that incapsulates our musculoskeletal system. The double bag theory, as described by Thomas Myers in Anatomy Trains, gives us a great visual as to how the fascial system is organized (2). Imagine putting your hands inside of a plastic bag and wrapping that bag around a wooden spool. The wooden spool is representative of bones and cartilage. The hard tissues are encased by the periosteum, which is the inner fascial layer represented by the inner layer of the plastic bag in this analogy. The ligaments are also included in this layer, as the ligaments and periosteum run in series with one another as we approach a joint in the body. Your hands inside of the plastic bag represent the muscle and, finally, the plastic on the outside of the bag represents a second layer of fascia that encases our muscle.

Fascia is made up of four different substances: gluey interfibrillar proteins commonly known as ground substance, reticulin fibers, elastin, and collagen. The ground substance is a watery gel that provides lubrication to the fascial system. This lubrication allows for the different layers to glide on each other more smoothly. Reticulin is a very fine fiber that can be thought of as an immature collagen. Reticulin is more prominent in the embryo and is largely replaced by collagen as we age. Elastin is a protein that is known for its flexible qualities. Tissues with high levels of elastin include the skin and ears. Collagen is also a protein, but it serves a different purpose than elastin. Collagen has the ability to lengthen under stress and to recoil in a manner similar to that of a spring (1). The Achilles tendon is an example of a tissue that has high amounts of collagen. Due to its ability to capture energy and return it to the system, collagen plays an extremely important role in the efficiency of human movement.

While muscles tend to only span one or two joints, the fascial system consists of long lines of pull that span the entirety of the musculoskeletal system. These long fascial lines allow us to distribute strain to adjacent fascial structures rather than relying on muscles to manage the forces solely at the tendons of their origin and insertion. This vast network helps us to better absorb the stresses experienced during movement as well as maintain the shape of the different parts of the body.

Fascia’s Effect on Movement Efficiency

Our fascial system is a big reason why human locomotion is so efficient. As we enter the absorption phase of gait, the forward and rotational forces experienced are absorbed by the fascial tissues, like loading a spring. These long fascial lines allow for us to absorb energy through the entire kinetic chain, rather than relying on an individual muscle. In fact, it has been shown that during the gait cycle, there is very little change in the length of the muscle fibers (1). Instead, the muscles act as a stiffness-adjusting system.

James Earls uses a balloon analogy to describe this concept in his book Born to Walk (1). If we were to blow up a balloon, the air inside would circumferentially tension the outer rubber membrane. In this analogy, the air inside the balloon represents our muscles and the rubber membrane of the balloon represents our fascial system. During the absorption phase, our muscles act as a hydraulic amplifier by tensioning the fascial system. This creates a shrink-wrapping effect that creates a more taut fascial system capable of easy force transfer and recoil.

As we progress into the propulsion phase, the energy that is captured during the absorption phase is used to return the body in the opposite direction. This recoil provides the body with essentially free energy to maintain its forward momentum. It’s actually been shown that up to 93% of the energy absorbed is returned to the system (1). Another benefit to this process is that it limits the amount of oxygen necessary for the working muscle since there is little change in the length of the muscle fibers. This is yet another way that the fascial system contributes to movement efficiency. In short, muscles aren’t so much responsible for shortening and lengthening during the gait cycle, but rather maintaining an optimal level of stiffness so that the collagen rich tissues can act as a spring and propel us forward.

The Back Functional Line

The Back Functional Line (BFL) plays a critical role throughout the gait cycle. The BFL begins with the distal attachment of the latissimus dorsi at the shaft of the humerus. From here, it runs distally to the sacrolumbar fascia where it crosses our midline and is picked up by the gluteus maximus on the opposite side. The lower fibers of the gluteus maximus wrap around the lateral femur and are then picked up by the vastus lateralis, which inserts to the tibial tuberosity via the quadriceps and patellar tendon.

The chart below will hopefully help to illustrate how the BFL functions throughout the gait cycle (the weightbearing phases of gait are in bold lettering). As we heel strike on the right lower extremity, we enter the absorption phase on the right side, which we will term flexion-rotation right. As we progress through this phase, the right knee flexes, the right hip flexes, and the thorax rotates to the right. During this phase the left BFL, consisting of the left latissimus dorsi, right gluteus maximus, and right vastus lateralis all lengthen. The lengthening of the BFL creates tension in the sacrolumbar fascia that we then store as potential energy. As we progress to the next step in the gait cycle, we enter the propulsion phase on the right lower extremity, which we will term extension-rotation left. Extension-rotation left consists of right knee extension, right hip extension, and left rotation of the thorax. During this phase, the left BFL shortens and the potential energy that was stored in our fascial system during the absorption phase is now returned to the system to propel us forward. So long as we continue walking in a reciprocal fashion, this loading and recoiling of the fascia continues to occur.

Another detail worth observing in this chart is what is occurring in the opposite BFL during this cycle. During gait, if one BFL is short, the opposite line is always long, and vice versa. This reciprocal relationship between the two BFL’s during gait is what enables our fascial system to wind up like a spring in order to maintain our forward momentum.

Creating Balance in Our Fascial System

Maintaining symmetry in our fascial lines is critical to preserving our efficiency during movement. Restrictions in fascia are communicated across the entire system like a snag in a sweater and these “snags” help to create our shape, which we tend to keep unless we alter it for better or for worse. In order to rearrange the fascial system, we must apply stress. Training is one modality that can be used to stress the system and initiate the change we are looking for. As the stress increases, the fascia begins to lie in the direction of the tensional part of the applied stress and will eventually remodel to accommodate these stresses.

This is where the ‘What’s That Strap’ comes in. Training with a ‘What’s That Strap’ allows us to strain our fascia through its full range of motion in all three planes. This allows us to balance the tensions in the fascial system, helping to give our movements a sense of effortlessness.

Now before I discuss some of my favorite ways to use this product, it should be noted that making lasting changes in the fascial system takes time. This process is much slower than attempting to build muscle. Due to the long half-life of collagen, a period of 6-24 months is required to make a thorough change in the fascial system (2). This speaks to the importance of patients continuing to exercise long after they are discharged. In order to make these changes stick we must be both consistent and persistent.

There are short-term benefits that can be seen from training with the ‘What’s That Strap,’ however. In a previous blog, I discussed how to navigate the performance pyramid as we program for our clients (click here). In this blog, I discussed how we work to improve range of motion first, followed by learning to control the newly acquired motion, before finally building capacity through a sound performance training program. Within this model, the ‘What’s That Strap’ provides us with a great tool to learn to control the range of motion we possess while coordinating multiple segments together in a fashion that resembles human locomotion. This is known as kinetic linking and can have a big impact on the efficiency of our movement.

The single leg hip hinge with a slider has been a staple in my programming for a while now when it comes to getting clients prepared to exercise. To perform this exercise, we will place the strap on our shoulder like a backpack and rotate in the opposite direction 360 degrees. Whichever hip the strap comes off of, that will be our stance leg. The opposite leg will be placed on the slider. Next, we will push the slider back as we take our chest over our lead leg to assume a running position. In the bottom position, there are a few things we are looking for:

1. We should be able to draw a straight line from our back ankle to our ipsilateral shoulder

2. Our front knee should translate forward to form a positive shin angle

3. We should feel our hip on our stance leg firing in the bottom position

In the video above, the right leg is the stance leg and the left leg is on the slider. When performing the exercise in this manner, we are training the left back functional line, which consists of the left latissimus dorsi, right gluteus maximus, and right vastus lateralis. As we approach the bottom position, the right knee flexes, the right hip flexes, and the thorax rotates to the right. Because the strap is pulling us into right hip flexion and right thoracic rotation, our BFL is being asked to eccentrically control the lengthening of this fascial line as we descend. Obviously, the ranges of motion experienced during this exercise are greater than what is observed during gait, but the BFL is functioning in a very similar fashion. As we return to the starting position, the joint positions listed previously are reversed and the left BFL returns to its normal resting length.

This exercise can be progressed by only rotating 270 degrees into the strap. This creates an anti-rotation component, which places an increased demand on the stability of the core and inside hip to maintain our balance. We can also add a diagonal reach in the bottom position to further lengthen the left BFL. This is referred to as an arm driver, which can be utilized to better feel the correct muscles engaging. As we reach diagonally across our body in the bottom position, we should be able to feel our inside hip engage even further.

We can once again progress this exercise by getting rid of the slider and undulating between the positions of absorption and propulsion in a single limb stance.

We can also use the ‘What’s That Strap’ to bias either absorption or propulsion. One way to bias absorption is by performing a forward lunge. In the video below, the strap is placed on my right shoulder and I then rotate 180 degrees to my left. This leaves the strap coming off my left hip. I then lunge forward with my right leg as the strap pulls me into right hip flexion and right thoracic rotation. With this setup, the left BFL once again must eccentrically control these forces. Again, we can add an arm driver to further rotate the thorax in order to eccentrically stress this line even more.

To bias propulsion, we can perform a step up. In the video below, the strap is placed on my left shoulder and I rotate to my right 360 degrees resulting in the strap coming off my left hip. I then place my left foot on the box and perform a step up. This setup shortens the right BFL, consisting of the right latissimus dorsi, left gluteus maximus, and left vastus lateralis. To further shorten this line, I can add an arm driver with my left arm to further drive right thoracic rotation.


Our fascial system plays a critical role in minimizing the metabolic cost of human locomotion. This is because the elastic qualities of our fascia act as a spring to aid in force transfer as we progress from the absorption to the propulsion phase of gait. Training the fascial system can be accomplished by moving through full ranges of motion in all three planes. The ‘What’s That Strap’ is a great tool for helping us to accomplish this task. I have become a big fan of this product due to its ability to stress our fascial lines as we mimic the triplanar motion seen during gait. Remember though, in order to make lasting changes in the fascial system, we must train it consistently as it takes fascia a significantly longer time to adapt than it does for muscle.


1. Earls, J. (2020). Born to walk: Myofascial efficiency and the body in movement. North Atlantic Books.

2. Myers, T.W. (2009). Anatomy Trains. Churchill Livingstone/Elsevier.