Below is an excerpt from Starting Strength which defines just exactly what is balance and how to understand and cultivate it. The full article may be read here.
What is Balance?
Balance can be defined as the ability to maintain one’s center of mass vertically over the base of support, with minimal postural sway. Let’s break this definition down a bit to make sure everything is crystal clear.
The “center of mass” (CoM) is a reference point representing the “averaged” mass of an object or person in space. In other words, if I were to take your body mass distribution in its current position and represent it as a single point, this would be your center of mass. For most humans of average anthropometry standing in anatomical position, this point lies somewhere within the pelvis, typically just in front of the sacrum.
How do humans detect imbalance?
So we’ve established that balance is maintained when the center of mass lies directly over the base of support (i.e., the mid-foot). Now let’s consider how humans detect imbalance. Although generally taken for granted, it requires a fascinating integration of three systems:
- The Vestibular system is located in the inner ear and is connected to multiple other areas of the brain and body through the brainstem. It detects linear acceleration and rotation of the head, and triggers reflexive compensatory movements to help us maintain equilibrium. For example, when focused on an object while rapidly turning your head to the right, you’ll notice that your eyes compensate by turning leftward in order to stay “locked” on your target. In addition, we can sense acceleration or tilting and adjust our posture appropriately due to the activity of our vestibular system, even in complete darkness. Impairments in this system typically result in dizziness or vertigo, and can result from various neurological disorders and diseases of the inner ear, trauma, strokes, tumors, medications, and drug/alcohol use (e.g. “the spins”).
- The Somatosensory system provides us with “proprioceptive” (position) and “kinesthetic” (movement) senses, among several others. The skin and musculoskeletal system detect and relay proprioceptive information along specialized sets of nerves to tell our brain about the position and movement of our bodies and joints. This is how you still know where your hands and feet are without looking at them, and how you can feel where your weight is being distributed across your feet. The sensory information coming from this system helps you maintain desired positions and stay in balance without having to watch your own body while you move. This is important since we can’t see our lower back during a deadlift, and we don’t actively watch our knees while we squat. Impairments in this system typically result from conditions affecting the nervous system (brain, spinal cord, and peripheral nerves) which commonly include diabetes, strokes, medications, and drug/alcohol use among numerous other conditions.
- The Visual system’s role should be intuitively obvious: a major component of sensing our position and movement is simply seeing it. Impairments in the visual system result in blindness and can result from things like diabetes, cataracts, macular degeneration, and glaucoma.
Interestingly, as long as at least two of the three systems we’ve discussed are working normally, people can still compensate enough to maintain their balance. For this reason you might encounter the “Romberg test” in hospitals or at drunk driving checkpoints, where the subject stands with the feet together and eyes closed (effectively “turning off” the visual system), and the examiner watches for significant swaying, unsteadiness, or falls that might indicate a problem with one of the two “remaining” sensory systems, usually proprioception.
How do humans overcome imbalance?
At this point I’d like you to try something: stand up right where you are and slowly lean forward onto your toes. You’ll immediately detect imbalance using the systems I just described, then you’ll notice feeling slightly uncomfortable as your calves, low back, and other leg muscles start tugging to prevent you from falling on your face. This all relaxes as you come back to the mid-foot balance point. Now, lean backwards onto your heels and you’ll feel even more apprehensive as your quadriceps and lower leg muscles start pulling very hard to prevent a fall backwards. You might even reflexively extend your arms out in front of you in an attempt to shift the center of mass forward again. This again resolves as you come back to the mid-foot. All of this “extra” muscular force is required to overcome the imbalance resulting from the center of mass not being positioned directly over the mid-foot. Read that again and be sure you understand, because this is fundamental. Muscular force is required to overcome imbalance, and therefore to maintain it.