The last post was about functional movement patterns. Here I will lay emphasis on stability. So what do we mean by stability? The dictionary defines stability as:
“1. The state or quality of being stable, especially:
a. Resistance to change, deterioration, or displacement.
b. Constancy of character or purpose; steadfastness.
c. Reliability; dependability.
2. The ability of an object, such as a ship or aircraft, to maintain equilibrium or resume its original, upright position after displacement, as by the sea or strong winds”
In physical therapy, as in other allied health fields, the focus is shifting to a wholistic approach. When one visits a PT and develops goals, it involves all of the above. In this case it would mean balance or the body’s ability to maintain an upright position at rest or after displacement, or in other words- shift of the center of gravity(cog) of the body. It also means, however difficult the task may seem, stay steadfast on the set goal for achieving that stability and that you may rely on, or depend on, your physical therapist to guide you through the process.
The center of gravity is a hypothetical point where the mass or weight (mass on which gravity is acting) of the body is concentrated. The cog of the human body lies just in front of the S2 vertebra, very close to the navel or belly button. In order for a body to be stable, the plumb line (simply a string with weight at the end-easily made at home) through the cog must fall within the base of support (BOS), not merely within, but rather at the center of the BOS. Let’s consider static stability in the standing position with the area under and in between the feet being the BOS. (Please refer to the pictures 1. and 2. below). Now, if we drop a plumb line from the cog or for practical purposes from the navel, it falls in the area between the 2 feet, in front of the ankle joints. In this position we are fairly stable. Consider a displacement of the cog forward, for example, when we walk or bend forward. This movement brings about a shift in the BOS, yet we do not fall at every step. This then forms the dynamic stability, with a constant change in BOS and muscular forces bringing about movement to maintain cog over the BOS. Very efficient is it not? Who knew?
Well, don’t just sit and read, go ahead and try it for yourself-find out where your cog is within the BOS.
Now let’s consider the dynamic muscular forces responsible for stability. Our trunk and spine is the central core from which extend our extremities. Trunk musculature is therefore extremely critical to maintaining stability, while the limbs are freely moving and reaching out during activities. We have all heard about the “core muscles” in this respect (I think “trunk stabilizers” or just “stabilizers” is a better term to refer to these muscles). Though there are several muscles in the trunk, we will consider only the prime stabilizers. The muscles that form a sort of corset around the trunk/waist are the Transverse Abdominus (abdominals) in the front, the Multifidi (back extensors) in the back and the Internal and External Obliques (also part of abdominals) and Quadratus Lumborum along the sides or flanks. (Please refer to picture 3. below). Also included are the pelvic floor muscles which sort of form the floor or base of the bucket, and the diaphragm, which is like the lid, with the corset being the sides of the bucket. This brings us to the importance of breathing and stability, and also explains why yoga and other forms of exercises use breathing techniques to train the stabilizers- it is because the stabilizers and diaphragm as well as pelvic floor muscles work in synchrony.
For stability, it is not only the strength in these muscles that matter, as is popularly believed. The timing at which these muscles contract during movement is very crucial to stability and efficient functional movement patterns. For example, for a back ache, your PT trains you to increase awareness of these stabilizing muscles by having you lie down when your body weight is supported and muscles are relatively relaxed. Therefore you can focus on “isolating” these muscles initially to activate them voluntarily. Stability must always come before mobility, and these trunk stabilizers must essentially fire first prior to those prime movers by as little as a fraction of a second. This allows you to experience an effective, efficient, and purposeful movement pattern. Once your muscles fire in the right pattern, this pattern is repeated in different positions through various exercises, and finally strengthened with the use of thera-bands, weights etc. Frequently, the latter two happen simultaneously.
Hope this gives some insight into the importance of keeping the trunk stable while the peripheral limbs are engaged in motion. Till next week…
Ami Gandhi is a licensed physical therapist in the state of California. She is the owner of StableMovement Physical Therapy, a small boutique practice in San Jose that offers patient centered, one-on-one, hands-on physical therapy.