Let's talk about the average American... This person spends 6-8 hours a night sleeping. Then, upon waking up, they hop in the car for a commute that lasts anywhere from 30 to 60 minutes. At the end of that commute is an 8 or so hour work day followed, again, by their commute. Once home, they eat dinner (or maybe they go through a drive thru on the way), and then what? It's very likely that they plop down on the couch for some good ol' fashioned TV watching... about THREE hours of it, according to the American Time Use Survey of June 2014.
So, what's the common denominator of all of these activities?
Beyond just the fact that the average American is sitting down for the majority of their day, it's also important to understand that sitting occurs in what is called the sagittal plane...
Our bodies move in three major planes of motion; (1) sagittal, (2) frontal, and (3) transverse.
The sagittal plane of motion, as previously discussed, is where sitting occurs. The sagittal plane draws an imaginary line down the middle of our bodies and splits us into left and right halves. As a result, movements in the sagittal plane are front-to-back, up-and-down kind of movements like standing, sitting, and squatting. Some common exercises occurring in the sagittal plane are the bicep curl, the seated row, squats, and lunges. Additionally, many weight training machines (otherwise known as assisted machines) create movement patterns that occur in the sagittal plane; seated leg curl, seated leg extension, standing calf raise, etc.
The frontal plane draws a line down the middle of our bodies as well, but unlike the sagittal plane, it splits our bodies into front and back halves and produces left-to-right, side-to-side movements. Exercises using the frontal plane are the lateral raise, side lunge, and lat pull-down.
Lastly, the transverse plane draws a line through our midsections and separates our bodies into top and bottom halves. The transverse plane produces rotational movements, and is seen the least often among common exercises. Some examples would be a russian twist, a seated ab rotation machine, and a transverse lunge.
So, as you can see from the list of example exercises, the sagittal plane is seen MOST often. It has the most commonly used exercises associated with it, and almost every weight training machine creates motion in the sagittal plane. Now, while the sagittal plane is not necessarily to be avoided during exercise, it's very important to utilize the frontal and transverse planes as well; equally as much, if possible.
Take a second to remember that majority of the average American's day is spent SITTING DOWN, and that sitting down occurs in the SAGITTAL PLANE... so if we make time in our day for exercise does it really make sense for us to continue to reinforce movements in the same plane we spend so much of our time in already? Or would it make more sense to strengthen our bodies in the other, weaker planes of motion?
The answer is - YES! It makes LOADS of sense to train our bodies in their weaker planes of motion. This will create major mechanical advantages in every day activities, because our bodies will have a better understanding of how to move most effectively and efficiently in ALL planes of motion rather than being, sort of, confined to the sagittal plane that we so often find ourselves stuck in.
Now, again, this isn't to say that training in the sagittal plane doesn't have its place. Everyone loves a good bicep curl or a traditional squat. However, this IS to say that it's very important to branch our from the sagittal plane; to leave our comfort zones and experience training in the front and transverse planes as well.
American Time Use Survey - http://www.bls.gov/news.release/atus.nr0.htm
NASM Essentials of Personal Fitness Training. Fourth Edition. Michael A. Clark, Brian G. Sutton, Scott C. Lucett. 2014.