Postural vs Phasic Muscles: Built-In Imbalance

If I were a betting woman, I’d bet a pretty good sum that you’ve never heard anyone complain that their butt muscles were too tight. Or that their back muscles were just too darn loose. Coincidence?  Au contraire, mon frere. It’s by design.

While the broader concept of muscle imbalances certainly generates a lot of buzz these days [even in the YFH Blog: Minimize Muscle Imbalances], there’s one significant aspect getting far too little attention. It’s the concept of postural and phasic muscles. 

The terms describe two categories of muscles, defined by their distinct functions and properties.  Postural muscles (e.g. spinal muscles, hip flexors, calves) are those most involved in maintaining our upright posture, while phasic muscles (e.g. glutes, deltoids, triceps, abdominals) are more responsible for moving us. But the more salient distinction is that postural muscles are programmed to become hyperactive, tight, and as a result, painful at times; whereas, phasic muscles are prone to become inhibited and weak.  You can see how these divergent tendencies naturally predispose you to imbalances.  In other words, by your body’s inherent design, muscle imbalances are the default–the rule not the exception. And they have major implications…

Consider which muscles you’re more prone to complain of being tight and/or painful: calves, pectorals (chest), low back, upper trapezius (upper back/back of neck)? And guess what they all have in common. Yep–all postural muscles.  And the muscles you can’t ever seem to strengthen enough: glutes (butt), lower trapezius (mid-back between shoulder blades), abdominals?  All phasic.  These aren’t complete lists, but these examples pertain to the most common problems like shoulder rotator cuff injuries, neck pain, and low back pain. 

Another important consequence of the postural/phasic divide: it can throw off your body’s delicate mechanics, making you more prone to injuries.  Though the details are too involved for this post, this issue is a major culprit in all of the ailments mentioned above. Fortunately, knowing the details isn’t as crucial as simply understanding the need to address what are very predictable deficiencies of the major postural and phasic muscles.

So when you think “balanced workout,” don’t just think front to back and side to side.  Think postural versus phasic and then focus on stretching the former and strengthening the latter. You don’t have to worry about making your back muscles too loose or your butt too strong. And I definitely wouldn’t take that bet if I were you.

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  1. I have something you might want to ponder on. I am 36 yrs old and had a total hip replacement a year and a half ago. I have went though three rounds of physical therapy. The first one being in home therapy. One of the major problems was acetubular protrusio. I had a lot of pain in my groin before the surgery. I got to where when I walked sometimes my hip felt like it would completely freeze up and then sitting was never comfortable. In fact, I was in so much pain all the time I decided to have a thr. Well, after I had it I immediately had pain in the groin. I worked hard on strengthening all the right muscles before and after surgery. Also have done a lot of stretching. I’m very frustrated because all of this hard work seems like it’s been for nothing. Almost every one of my muscles surrounding my left hip are super tight!!, especially my pectinious, gracillis, and glutes. When I go to my masseuse it seems like I have relief and they relax only for a few days. Then the tighten right back up. The more I do the more they tighten. Heaven forbid I try to bring my left leg inward( bent at the knee). Also have swelling in the top of my left foot on the outter part. Sharp pain in groin when coughing and still hurts in groin when I pull leg up to put pants on. No known hernias, good X-rays, MRI, and ultrasound. Any thoughts?

  2. I tend to have low back (lumbosacral) pain. I have tight lumbar area and loose buttocks all my life. I do yoga, GiGOng, walk daily, play tennis, snowshoeing etc.


  3. Hi,

    I have done postural therapy for pain relief for over 13 years, so I am completely behind you when you talk about how imbalance throws off the bodies mechanics and makes people prone to injury. While many people might have tight “postural” muscles and weak “phasic” muscles as you describe, it is not always the case. You start by saying:

    “If I were a betting woman, I’d bet a pretty good sum that you’ve never heard anyone complain that their butt muscles were too tight. Or that their back muscles were just too darn loose.”

    I have seen many people with tight butt muscles and excessively loose back muscles (and I know you are talking just about low back muscles). I know it is easy to use the postural vs phasic muscle idea, but people often get confused about what it means the muscles are doing and that muscles always act this way (they don’t).

    One of the most common reasons people have low back pain is because they have weak and loose low back muscles. This is usually a compensation for lack of pelvic strength and function, so rehabilitation involves restoring hip mobility and function but also strengthening and shortening the lumbar erectors.

    You also state that:

    “Consider which muscles you’re more prone to complain of being tight and/or painful:… upper trapezius…”

    The upper trapezius is painful in many people not because it is short and tight (as most people believe) but because it is long and taut. The upper traps become painful because they are lengthened beyond their design resting length and then made to do an excessive amount of work. Most people treat this by stretching and massaging the upper traps, which actually lengthen the muscle more exacerbating the problem. Instead people should stop focusing on the symptom of a painful upper trap and focus on the cause of the tautness. This is usually an excessively rounded thoracic spine and forward hinged shoulders. Changing this and then letting the upper traps shorten to go back to their normal length and tension will take away the pain caused by excessive length.

    Balanced workouts are very important, and I believe the concept of “straighten before you strengthen” is even more important. Doing any exercise (especially weight/strength training) with imbalanced posture will end up strengthening the imbalances instead of correcting them. Doing specific therapy exercises to balance posture before working out is key to improving postural imbalances over time and decreasing chance of injury and improving performance.


    • Hi Matt,

      Thanks for the very thoughtful comment. I actually agree with almost everything you’ve said, but you’re getting into a much more detailed discussion than the post was aiming for. Much of what you’re bringing up are exceptions and/or more nuanced points that require a much lengthier discussion. I first want people to have a basic understanding of the broader concept and its general principles. Another post of mine–here–addresses more of what you’re getting at, and might make you rest little easier on the matter. THanks again, appreciate the comment.