Think Trunk Not Core: PureTorque and the Power of Rotational Force Potential

In this blog we’re on a quest to understand our core muscles and how they react while performing spinal rotation, swinging, or twisting motions with the PureTorque.

As many of you already know, what sets the PureTorque apart from the competition is its ability to directly load your trunk muscles and maximize your core’s training effectiveness. But how does the core relate to the PureTorque’s unique ability to produce force in rotation?

Let’s begin with an overview of the core. Most people believe that the core is made up purely of our abdominal muscles — our obliques, rectus abdominis, and transverse abdominis muscles.

In fact, the core extends to our back, hips, and upper legs. In physiological terms, that’s our spinal extensors including the multifidus, iliocostalis, longissimus, and quadratus lumborum.

To help explain this further, let’s forget the term ‘core’ and instead refer to it as ‘the trunk’, a concept taught to me by Tom Purvis, creator of the Resistance Training Specialist (RTS) Mastery program where I received my professional training. 

Renaming the core as the ‘trunk’ offers a more accurate vision of the relationship between these extraordinary muscle groups.

The core, which means center, or middle, is a force transmitter from the ground up.  The core of a tree trunk is in the center, but you must also look to the roots and branches where the force transferred through those limbs. 

Just like a tree, your trunk muscles can influence almost any muscle that attaches to the spine, ribs, or pelvis, including the glutes, adductors, hip flexors, hamstring, and lats. 

In order to get the best level of understanding from the blog, let’s examine some of the terms and concepts that we’ll be addressing. The co-contracting between oppositional muscles will feature prominently. 

In the training world, we are conditioned to believe that there is a “law of reciprocal inhibition” — that an antagonist muscle cannot contract while the agonist is contracting. 

Take, for instance, the common misconception that the triceps relax when the biceps contract in a bicep curl.  This belief has been disproven a multitude of times. 

In the bicep curl example, your biceps can only contract and move at the rate that your triceps will allow.  They are working together to create elbow flexion.  Your biceps are fighting the resistance, and your triceps are managing your elbow. 

With that understanding, it’s difficult to use oppositional terms.  RTS has coined the terms ‘resistance fighter’ and ‘joint manager’. For the purposes of this blog, those are the right terms to use for this relationship.

Let me explain. Around every axis, you have muscles working in active coordination, called co-contraction. That means that one side is creating motion while fighting against resistance, and the other is managing the joint, allowing motion.

The other RTS terms that we’ll be using in this blog are moment arm (MA) and line-of-pull. The moment arm is essentially the perpendicular distance of the line of force to an axis.

This ‘moment’ relates to the muscles’ effectiveness at producing a torque (the force around an axis).   The line-of-pull is a lot easier to understand.  It’s simply the direction that the resistance is trying to move you towards.

The relationship between the line-of-pull and the alignment, orientation, and moment of our corresponding muscle fibers will dictate how effective we are at reverting that resistance.

Accompanying this blog is a series of illustrations created by Eugen Loki of Pheasyque, a superbly talented collaborator. Reviewing these illustrations will help you better understand how our body produces force in rotation. Let’s get started.

The Neutral Position

Neutral position
The Neutral Position

Let’s begin with the neutral position. The neutral spinal position offers a snapshot of your muscle fibers on the brink of performance. 

There is no bias towards any one position or direction, but the body is prepared to effectively contract or move in any direction.

Since this illustration is showing a line-of-pull into the left rotation, your right rotators are engaged to create motion and resist that directional pull.  The left external oblique and right internal oblique (your right rotators) are highlighted in black. 

Highlighted in yellow are your joint managing co-contractors, your right external oblique, and your left internal oblique. 

You’ll also see the rectus abdominis highlighted in yellow. While they aren’t responding to the line of pull, they are contracting to create some compressive force in your trunk. 

As we move through the sections, please take into account the alignment of fibers and how it relates to the line-of-pull.

The Resisted Right Rotation

Right rotation position
The Resisted Right Rotation

Here we see a person moving into a resisted right rotation.  They are past neutral which you can identify by the fiber direction of their rectus abdominis (RA), highlighted by the centered yellow arrows. 

As we move into the right rotation, the RA starts getting a “line-of-pull” or moment to left rotation. In effect, it is becoming a joint manager. 

At the same time, the left external oblique and right internal oblique — identified with black arrows — drive this part of the rotation. 

Earlier in the introduction, we identified trunk rotation participating muscles as ‘resistance fighters’ (creating the motion) and ‘joint managers’ (actively co-contracting to allow the motion). 

In this section, the muscles creating the motion are black, and their co-contractors are in yellow.  As you pass the neutral spine position, the tension created by fiber alignment and the length-tension of the yellow highlighted fibers begins to get into a position to pull you out of that rotation.

Over the course of the section, you can see how the muscles highlighted in yellow are aligning more with the line of pull, and that muscles that weren’t involved (RA) are now engaged due to fiber alignment. 

At the same time, notice how the fiber alignment of black highlighted muscles are starting to fall outside the line of pull.  These two factors are minimizing your ability to counter the resistance.

End Range Right Rotation

End range right rotation
End Range Right Rotation


In this section, we are examining end range right rotation.  Compare the fiber direction of the black fibers to that of the yellow ones.  Everything pulling you further into the right rotation is no longer in a position to do that anymore.

Furthermore, all the muscles (in yellow) that are controlling motion with their co-contractions are in an even better position to actively slow you down and stop you. 

This is incredible; your body has a built-in, ultra-efficient structural mechanism to produce force, counter that force, and then pull out of that end range position.

The Transitional Left Rotation

Transitional Left Rotation
Transitional Left Rotation

This section shows what happens when we move past neutral and into left rotation.  We would traditionally call this the eccentric part of the exercise.  The line-of-pull is pulling you into left rotation with the right rotators allowing that motion, highlighted in black, controlling that return. 

Take note of the fiber alignment here, as compared to the previous section.  At the end of the right rotation, the muscles in black are no longer creating rotation. 

In the previous section, the rectus abdominis was controlling the end range (in yellow), while in this section it is fighting the resistance (in black).

What happens next?  Before you move to the next section, picture yourself as a lefty swinger loading yourself into a left rotation.  Imagine that you are gathering as much potential energy as you can. 

Now, picture yourself getting ready to explode into a ball, or a puck, or a strike.  Look down and see how those muscles are prepping for your attack.

Begin Right Rotation

the begin right rotation position
The Begin Right Rotation Position


Look at the alignment of those black arrows! Pause, and look at the direction of the yellow arrows.  From this position, your right rotators are in the best possible position to create rotation and the muscles that would slow you down cannot do that! Where you have the ability to generate the most force, your body is designed to allow you to do that while also removing impediments. 

I hope that these illustrations help give you a better sense of how this segment of our trunk transfers force in rotation, primes potential force output, and efficiently stores and reverts that force. 

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Puretorque® is a product of Lyron Advanced Technologies.