Why Can Training the 'Mirror Muscles' Cause Pain?

Sitting can cause chronic pain, but so can non-functional exercise.

Posted Sep 08, 2017

We begin my summer Pilates class assessing what the participants want to work on. We are all women—cashiers, dental hygienists, language teachers, students, but also movement professionals such as physiotherapists, massage therapists, fitness instructors. Instead of worrying about losing weight or getting more toned abs, we all look for exercise to alleviate pain—foot pain, lower back pain, shoulder pain, upper arm pain, neck pain, wrist pain. Has feeling pain free now surpassed "looking good" as women’s fitness goal? Why do we feel so much pain although we all exercise?

While pain may not stop us from working, it limits what we can do in our every day lives. The psychological effects are also debilitating: suffering from persistent pain is stressful, creates anxiety, and can be depressing. Then what makes us, seemingly healthy women, experience pain to the extent that we have to worry about it?

One thing that many of us shared was sitting during the workday. I, for example, sit most of the day in front of my computer; several of the other participants spend their days in a similar posture.

Although chairs are designed to provide rest, sitting can cause pain because some body parts are over stressed while others do no work at all. This is the result of what exercise physiologists and bio-mechanists call plasticity. Plasticity is a mechanical property of the muscle tissue to deform when it is loaded past its elastic limit. When past this limit, considerably more deformation can happen with only a small increase of force. A long-term, repetitive stress and the following deformation can cause micro trauma in muscle tissue. Sitting in a chair can have these serious consequences when some postural muscles are overloaded: over time, the muscles adapt in a faulty sitting posture that then results in deformation of the back muscles and shortening of the chest muscles in the front of the body. This leads to a reduced range of motion and pain.

It was clear that some of my summer Pilates participants’ pain was a result of faulty sitting posture: hunched up shoulders, inwardly rotated arms, forward jutting head. This type of pain from long-term repetitive stress is often described as chronic pain: pain persisting for a long period of time, yet not caused by a particular trauma (such as an accident). In addition, chronic pain experiences are subjective and often it is not easy to identify the cause that can lie elsewhere from where we actually feel the pain. Nearly 25 million Americans experience daily chronic pain with added psychological consequences such as sleep disturbance and mood changes.

As constant sitting is known to cause pain, one solution is to switch to a stand-up desk. Many of my colleagues have opted for these types of desks and also often stand up during long meetings. For example, one of my colleagues explained that her thigh pain has disappeared with a stand-up desk. My own experiments with standing up, however, were cut short when I realized that I could stand up for only a short time due to pain in my lower back. Obviously, simply standing up does not necessarily alleviate pain. Neither does exercise.

Like standing up, exercise does not automatically alleviate pain. In his work, personal trainer Anthony Carey (2005) warns that exercise might exacerbate muscle imbalances acquired through the habits of daily living. Sitting on an exercise bike or on weight training machines in the gym after sitting all day at our desks, he points out, most likely stresses our already over-stressed muscles. Our desire to tone what he calls the "mirror muscles" (arms, abs, glutes, legs) might improve our looks, but not necessarily the function of the body. The fitness industry has adapted the preference for mirror-muscle exercises from the bodybuilding community that trains for a specific purpose: to build large muscles by isolating and overloading specific muscles or muscle groups. So it is that bodybuilders are judged by the looks of their bodies, not by their functionality or movement ability. For Carey, such typical gym exercises as hamstring curls, biceps and triceps curls, leg-extensions, calf raises, or bench presses are non-functional, but bodybuilding-specific exercises. Therefore, while machines can be excellent learning tools for beginner exercisers—they guide us through the correct pattern of exercise to effectively isolate the targeted muscle and support the rest of body to allow the exerciser to focus purely on the intended muscle—they, Carey observes, tend to train the same muscles that are already tightened in a sitting posture and do no strengthen the weak muscles in the upper back or the trunk.

To alleviate chronic pain resulting from postural imbalances clearly requires a change in thinking. Toning the mirror-muscles or exclusively doing cardio to lose weight without a concern for strength or flexibility can be more detrimental than beneficial. In the worst case, the resulting pain might make us stop exercising entirely. Some pointers from the proponents of functional exercise for adopting a new exercise attitude include:

  1. It is important not to deny that one has pain and even more importantly, that it requires effort, both mental and physical, to recover from the pain. While taking painkillers might provide relief, it is crucial to assess the actual cause for the pain, be it a previous injury or postural fault due to habitual movement patterns.
  2. The most common reaction to pain is, naturally, to avoid it. I do not want to stand up in meetings because my back hurts while my colleague avoids sitting because of her leg pain. Although this is understandable, we should also find out why we are in pain when performing movements that the body should, naturally, be able to perform. Thus, instead of simply avoiding the painful movements, we should attempt to find out why standing or sitting, for example, are painful for us.
  3. As it has taken time to develop a faulty posture, it will also take time to recover from it and correct it. This is work that has to be done individually and thus, we need to be committed to perform a program that strengthens the weak muscles and stretches the tight ones. Such a program often includes movements or exercises that we are bad at and thus, avoid or initially feel uncomfortable doing but they, nevertheless, are necessary for ‘correcting’ any muscle imbalances.

In my Pilates summer class we were all active women, but obviously we were not aware of what actually caused the pain we experienced. How were we to find out? This is particularly difficult as we can feel the pain in a different place from its actual cause. Carey (2005) provides persistent wrist pain experienced by someone who sits all day typing in front of a computer as an example. This pain can actually be a result of weak abdominal muscles that, instead of supporting the upper body, let the wrists take its weight. The wrists, then, have to support the upper body as well as do the work of aligning the typing hands. I found that my own foot pain is actually a result of faulty ankle alignment caused by faulty knee alignment caused by faulty hip alignment. The body works as a unit: when one part is ‘out of whack,’ over stressed, or weak, the other body parts compensate for these faults. Over time, this compensation for postural faults, however, can result in pain. For this reason, it is often not enough simply to attend to the body part in pain.

If pain can be the result of such a complex chain of events, how are we to know about these things? Although it is possible to work alone to improve one’s posture, it is also important to have a professionally performed alignment assessment before embarking on a new exercise program. One solution can be to enlist the services of a personal trainer for help.

As a personal trainer himself, Carey (2005) emphasizes the importance of building a program based on an individual postural assessment instead of a standardized program. Even if a standard program is well designed and thus, well balanced, it may not account for individual bodily deviations and can make some problems worse. For example, some exercises that technically speaking are beneficial, can be harmful for some individuals. ‘The plank,’ common in most Pilates repertoires, is such an exercise. While it definitely targets the abdominals, it is also a very demanding exercise that requires good upper back and lower back strength in addition to good body awareness to perform it correctly. Most beginner exercisers do not possess the strength or proper body placement to benefit from the plank. On the contrary, it can cause lower back pain when performed incorrectly. If such common exercises as the plank can be harmful, what can we possibly do in our Pilates sessions to alleviate, not cause, pain?

It is obvious that finding a good, well-informed, and well-educated fitness professional is crucial for a functional exercise program. In my Pilates class, we managed to alleviate some of the back and foot pain by moving away from training the "mirror muscles" to focus on the muscles that move the shoulder blades (upper trapezius, rhomboids, serratus anterior), the hip rotation muscles such as the piriformis, and the toe flexors and extensors. While one class cannot undo weeks or even years of stress on certain muscles or miraculously cure one’s postural faults, it can be a beginning of a path for a different exercise attitude. With the functional focus, we aimed to build new physical and psychological dimensions for exercise and at the same time, gained an entirely new exercise vocabulary to train "functional muscles" instead of mirror muscles.


Carey, A. (2005). The pain free program: A proven method to relieve back, neck, shoulder and joint pain. John Wiley and Sons.