Planes of Motion

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.