Relaxation and center of gravity are the first two concepts of the Six Physical Points in I-Liq Chuan.  The two concepts are distinct yet closely interrelated.  Without first achieving understanding of the center of gravity (i.e. stacking up the body structure over the center of the feet), the body cannot fully relax.  As it turns out, not understanding the center of gravity not only affects your muscular tension, but it also affects your movement patterns.

When the structure is stacked up over the feet, the muscles can relax and the skeleton can bear the brunt of the gravitational force.  When the structure is off-balance, the body will activate muscles to preserve stability.  With those muscles tensed to preserve stability, they become less available for generating usable force.  A further consequence of the tensed muscles is that muscle coordination and firing patterns change.  To illustrate this, I’m going to borrow material from physical therapist Bill Hartman:

“Ever have an athlete that no matter how hard to you try to impact [ankle]
dorsiflexion, you don’t see the changes in his performance during
ground-based activities?

You mobilize his ankle, and his squat doesn’t change.  You stretch the
calf, and he still has a premature heel lift when he walks.  You have
him hop up on the exam table, and it looks like he should have enough
dorsiflexion as you move the ankle through a full range of motion.  You
put him back on the ground.  No dice.

[…]

Your mobilization and stretching may have addressed the physiologic
stiffness that would prevent normal ankle mobility, but if your athlete
has poor control of his center of gravity, the stiffness will persist to
maintain stability.  The result is a neurologic barrier to performance
and greater risk of injury.

Got an athlete with plantar fasciitis, anterior knee pain, groin
pain, piriformis syndrome?

Consider looking at the factors that influence center of gravity and
the associated alignment and muscular activation patterns.”

Understanding the center of gravity is pivotal to achieving relaxed movement.  And as I understand it now, it is also crucial for just moving properly.  A body tensed by being off balance can develop a host of structural misalignments and altered kinetic chain firing patterns.  When the center of gravity is restored, movement quality can improve and the body can more effectively generate force.