I’m going to discuss a topic that I always thought was irrelevant during most of my education, and one which provides many people with far more confusion than clarity. “Planes of motion” are ways in which we can categorise, define, and analyse movements. There are three primary planes you might consider: Sagittal which are movements going front to back, Frontal which is side to side, and Transverse which is rotational.
This is a very simple description of something which was so complicated when I was taught it that I can only draw the conclusion that my teachers did not understand it. To fully understand the planes of motion you need to know the axes of the body- but I’m not going to discuss that topic in full because I also think this is why the confusion arises.
Why the confusion?
When I first did my personal training course and was asked to write examples of exercises in each plane, I wrote something like: front raise for Sagittal, lateral raise for Frontal and pec fly for Transverse. Based on the axes of the body this is technically correct. And is exactly why I didn’t understand the point. Where was the utility in these definitions? How did it impact upon my programming? What benefit did the client see from working those three movements rather than three other exercises in other planes? Why the differentiation?
This focus on defining the movement based upon the axis doesn’t really work that reason. If we take out the axis and just think broadly about the movement, then we can see the distinctions more clearly. Stepping sideways uses muscles very differently than stepping forward or rotating. To label a bench press as a transverse plane movement never made much sense to me. I understood that the humerus is moving around a longitudinal axis which makes it a Transverse plane movement; but I just didn’t see the point.
The issue with movement is that it is integrated. More than one plane is being used at one time in most activities. Most muscles also have more than one function which typically makes use of different planes. The glutes for example can extend the femur (Sagittal), abduct the femur (Frontal) and externally rotate the femur (Transverse). It will do all of these to some degree during gait. Same with a squat. Knee valgus is typically a compensation pattern that takes place when the strength of the Sagittal plane muscle action is insufficient. The traditional concept of “valgus” is a movement that occurs through the Frontal and Transverse planes to achieve the Sagittal goal of knee and hip extension. Is the squat then a multiplanar exercise? I would still argue no.
How do we move?
The inconvenient truth is that all movement is rotation. Sagittal and Frontal planes movements are an illusion of straight lines due to the fact that all joints are built on helical angles. What appears as a straight line is in fact a number of rotations cancelling each other out. Lifting you knee in front of you is flexion, and lifting it to the side is abduction. But what if you lift it out at 45 degrees? Where is the line where it stops being flexion, and starts becoming abduction? The answer is that there is no such line. The movements blend together which is why there is no separation between the two. In fact, when you look at what is taking place in the joint itself, both these movements are simply expressions of external rotation. So they would therefore be Transverse plane. The most accurate representation of how the body moves is not through planes, but through the broader concepts of compression or expansion. The planes of motion should be used solely as descriptive concepts and not as models of how we move, should move, or should train. Within this model, valgus is not really a thing. All extension is internal rotation so valgus, again, is an illusion. The line between a valgus squat, and a non-valgus squat is arbitrary.
For me, in order to reduce the dynamics of complicated movement to a single plane of motion in order to have a discussion that is at least productive, you must consider the most important structures of the body. The pelvis and the rib cage. If either of those are rotating, then to me it is a Transverse activity. If either is laterally tilting, then it is Frontal plane. If either are flexing or extending, then it is Sagittal. A bench press is therefore Sagittal. As is a squat. Running, however, involves all three movements of both rib cage and pelvis. Therefore, we can confidently describe it as a multiplanar exercise.
Balancing your workouts
As mentioned, these global definitions are not accurate representations of movement but can at least be used to discuss and categorise movements in programming. However, I still don’t think it is adequate to simply include Frontal and Transverse plane movements in isolation alongside your Sagittal workouts. Some or most of your training should involve truly multiplanar movement. Considering the body in this way eliminates the concept of agonists and antagonists. The "push-pull" model of muscle action might work if straight lines were real but they are not. Muscles are simply squeezers and often times work together on opposing sides of the joints. Many trainers will talk about balancing your workouts by targeting antagonistic muscles. Balancing push work with pull work. In a world with a Sagittal plane this makes sense but when we look at the pecs and lats as the primary pushers and pullers, this approach only serves to reinforce Frontal and Transverse biases. Both these muscles adduct and internally rotate the humerus. Two out of three planes are being hammered in one direction- despite the goal being “balance”. Adduction by the pecs is technically transverse and adduction by the lats is technically frontal; if we work based purely by axes. But this is not how to construct a multiplanar workout for balance. This example highlights why the traditional concepts of planes and axes of motion really make no sense. If you have the wrong model you will come to the wrong conclusions.
As a rule of thumb for three dimensional training: any time you are bilateral throughout a movement you eliminate two out of three planes. You cannot laterally tilt or rotate without shifting your weight to one side. We must also consider the fact that body is not symmetrical. Your pelvis is shaped in such a way that it usually rotates slightly towards the right. Your organs are lopsided with colon descending on the left, liver sat mostly on the right, your heart slightly to the left, your right lung about 1/6 larger than the left. The muscles reflect this- primarily your diaphragm being larger and higher on the right.
This means that no bilateral movement will ever be truly symmetrical, no matter how it looks from the outside. You will always have rotational tendencies towards one side. Even if you work against it the internal torque is unidirectional. Training from a unilateral stance with multiple planes truly is the only way to establish balance and symmetry in the human body. This is why it plays an important role in creating better symmetry, far more so than simply strengthening each individual limb.
In short: the planes of motion do not actually exist. Think of how you open a Lindor chocolate: you pull the ends in a straight line but as the wrapper uncoils the movement takes place through rotation. When a plane flies directly from one place to another on the globe, and you plot that line on flat paper, it becomes a curve. Straight lines cannot exist in human movement because they are superimposed upon a rotational structure. If we still choose to use planes of motion as descriptive tools however, we need to use a definition that actually provides some meaningful differentiation. This is done by considering the rib cage and pelvis, rather than imaginary axes. The need for these tools becomes less and less when we simply apply a training approach that operates in three dimensions. The first step in this process is to stagger your stance, and train unilaterally. Base your training around what you see in natural movement, and not what is available to use in a gym. Once you can unlearn the indoctrinated approach it actually simplifies coaching and provides far more options for programming, and likely will yield better results for improving athleticism and movement comfort and competency.