Why are our bodies generally symmetrical

Humans aren't symmetrical.

We're not born symmetrically, and our daily rituals only make us less so.

So why is symmetry seen as a "golden" rule in training? Why must we always perform the same number of reps on one side as the other?

I have no problems whatsoever giving an athlete or client a 2:1 or even 3:1 ratio of reps for their left vs. their right side or vice versa.

If you train a dysfunctional asymmetrical body symmetrically, you aren't going to get very far. You're often just reinforcing the problems that are already there.

The Asymmetrical Human Body

Our diaphragm, a major muscle of inhalation, has a bigger right dome than left.

This is a fundamental core of our asymmetrical body, and it has huge implications for posture, health and performance.

I won't get into the minutiae, but our right lung actually fills our left chest wall, and vice versa.

Due to asymmetries such as the right dome of our diaphragm being larger than the left, we're able to fill our left chest wall more easily than our right.

To survive, our body naturally orients to bringing in air in the easiest and most energy-efficient way possible.

With our body naturally designed in a way that makes it easier to fill up our left chest wall, that orientation often looks like this:

The left side is opened up via pelvic orientation to the right and our trunks to the left so we can really breathe into our left chest. Your body will always take the path of least resistance to take in air, and this is usually it.

However, this orientation has a cascade effect on muscles throughout the body. Certain muscles on the right side become overactive while certain muscles on the left side become under-active, and vice versa.

Many times, I see athletes better able to load/be strong in their right side in bilateral exercises and push (jump) better off their left side.

The 'Explosive' Left Side

Due to the typical forward orientation of the left pelvis, the femur generally is in an externally rotated or "turned out" position. This leaves the left pelvis and leg in an extended, "exploded" state.

Due to this orientation, the following muscles are all generally overactive:

  • Left gluteus maximus, as it pushes the pelvis forward and externally rotates the femur
  • Posterior fibers of the left gluteus medius (outside hip muscle), as they abduct the pelvis
  • Left quads/hip flexors, as they pull the pelvis forward

I believe this is why so many athletes feel more comfortable jumping off their left leg. Their standard body orientation already has them in a position where exploding off their left comes more natural.

The 'Strong' Right Side

The right side is the inverse of the left. It is oriented in a "loading" phase of gait where the pelvis and femur are posteriorly and internally rotated.

Due to this orientation, the following muscles are all generally overactive:

  • Right adductors (inner thigh muscles), as they pull the center of mass to the right side
  • Anterior fibers of the right gluteus medius (outside hip muscle), as they internally rotate the hip and femur
  • Right obliques (side abdominal muscles), which side-bend the body to the right
  • Occasionally, the right hamstring is all overactive, as it pulls the pelvis back

Essentially, the muscles that are over-active on the left side are under-active on the right side, and vice versa.

I believe this is why I see so many people shift more into their right hip during bilateral lower-body exercises. Their center of mass is being pulled to the dominant right side where they're stronger and better able to hip shift.

When Asymmetry Becomes an Issue

Our body is naturally asymmetrical, so the idea that perfect symmetry should be the goal is misguided. However, issues can occur when these asymmetries become too exaggerated.

If the objective assessments I run on a client determine a dramatic left side weakness, I have no issues giving them more single-leg strength development on the left and more single-leg plyometric work on their right.

Again, training asymmetrically is advantageous if the circumstances call for it. I do not do this blindly. There needs to be context and a rational thought progression.

For example: I will give a 3:1 ratio of Wall-Supported Split Squats, where I am having the client feel their left adductor, gluteus medius, and obliques.

Why would I give them an equal share on the right side when those muscles are already strong?

If I did, I wouldn't be assisting them in restoring a more neutral pelvic orientation that can alternate hip shifting. The left side needs to be able to catch up to the right in terms of loading and the right needs to catch up to the left in terms of propelling, or pushing.

Keeping a someone's training perfectly symmetrical is easy, but it's rarely right. An asymmetrical body demands an asymmetrical approach.

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