So This Is How the Muscles Work?

Almost every muscle building, physique training and injury rehabilitation article and book tends to rely on what appears to be scientifically accurate and precise analyses of which muscles are doing what, when and how. Every unsuccessful training program, every injury, every alleged “muscle imbalance,” every insufficiency in balancing capability, every inefficiency in so-called “functional” fitness is attributed to some pattern of muscle involvement that does not meet with some unwritten ideal.

All too seldom are questions raised about the validity of this idealized or personally hypothesized model against which all movements and muscle patterns of recruitment are judged, so it is not surprising that these traditional models and ideals are proliferated. Of course, now and again, some relatively novice students will emerge with some probing questions that deserve some serious response. Here is one such question from a university student who apparently has been suffering great frustration at the hands of every teacher and article that he reads on muscle action:

“All of these so-called "expert" analyzes and opinions about muscle action have made me realize how therapists and kinesiologists in general have completely different answers to the same anatomical questions. Ask 100 of them how something works or how to best do a movement and it seems that you will get 100 different answers. Why is that? I can't think of any such cases occurring in any other science (where every contributing factor seems to be well known and documented - not like UFO sightings or the existence of God). Take the squat and bench press, for instance. There should be no discrepancy between these supposed experts in human anatomy in what is dangerous and what isn't. Old wives tales should have no effect on the opinion of a doctor or a scientist.” This is a very important comment and worthy of a very detailed commentary, because it concerns an issue which is central to what is discussed in every training and therapeutic course.

Kinesiological analysis based upon the standard muscle action charts indeed leaves a great deal of room for individual opinion, especially if one tries to explain any complex sporting movement as the sum of what each contributing joint does separately. The whole motor action is NOT simply the sum of the individual actions of each isolated joint that is assumed to take part in the overall movement.

In addition, any complex movement involving much of the body for stabilization and mobilization (movement) is not necessarily the result of actions by muscles which cross or move the joints that seem most important to the given complex movement, as was noted by the eminent Russian scientist, Dr Bernstein, many years ago. He, of course, was one of the earliest to stress that “the body knows only of movements, not muscles” (I shall have to discuss the limitations of this oft-quoted comment in a future article).

Measurement of Muscle Action

Let us embark upon our quest to understand joint movement by examining how scientists establish which muscles carry out a given joint action. The major methods used are the following:

1. Analysis of cadavers, where the anatomist examines where the muscles and other soft tissues are located, where they attach and how they move if one tugs on given tissues or bones. A model based upon similar principles of how engineering structures and machines are built is constructed and used to infer how each different works for every joint action in the body. Sometimes, the muscles may be stimulated electrically to see how the joints are moved. Of course, every body displays its own idiosyncrasies and differences, so, while we can identify commonplace actions, we cannot always be certain that they take place in exactly the same way in every person.
2. Measurement of the electrical activity (EMG - electromyogram) of the muscles is measured during real-life movements. This study is known as electromyography and may be carried out in two ways: (a) with electrodes placed upon the surface of the skin directly above the muscles that we wish to analyze (b) with fine wire or needle electrodes inserted or "injected" invasively into the deeper layers of muscle or specific individual muscles. The first method adds up the contributions of deeper and superficial layers of the same muscle and those of adjacent muscles, so they often do not tell us about the action of individual muscles. The latter method often poses risks to the subjects and cannot be used where there is considerable complex movement.
3. Palpation or pressing with the fingers is used to estimate which muscles are involved and to what degree, usually under static or slow clinical conditions. Several therapists, such as Kendall, have written entire textbooks on using this palpatory approach to test muscles, but, at best these subjective methods offer a very approximate and limited view of a restricted range of muscles under non-sporting conditions.
4. Modern "radiographic" methods such as MRI (magnetic resonance imaging) are now being used to offer another non-invasive method to examine what the muscles and even parts of the brain may be doing during non-sporting actions which can be assessed within the limited space of the machines being used. Though the results may appear to be most impressive, this method also has its critics and as yet, does not offer the much sought-after "missing link" of functional anatomy.

From the above, we may note that invasive electrodes to measure EMG from many muscles and MRI, as well high speed video and other biomechanical systems, therefore, are being used in an attempt to make kinesiology less subjective. However, even that complex approach does not yield all necessary information, so there will always be a great degree of variability in interpretation. Some of the most important limitations of traditional kinesiological analysis are:

1. It does not take into account the contributions to movement by distant muscles which do not cross the joints involved in the action.
2. A given external movement pattern is not necessarily produced by the identical muscle actions every time that the movement takes place (this issue was also discussed by Dr Bernstein and in a recent copy of the Scientific American)
3. Recent research has shown that biological systems like the body do not necessarily rely on highly predictable, determinate, linear events in which one action always results in a specific result or in a result whose magnitude depends directly on the original stimulus. Thus, the body often tends to invoke processes that scientifically are known as nonlinear, indeterminate, random, chaotic or "fuzzy." So, a small change in one muscle can produce either a small change, no change at all or even a large or damaging change in the external movement. Some workers who believe that injuries are caused by measurable "muscle imbalances" invariably neglect to mention the important fact that apparently insignificant or indiscernible changes in muscle activation or lack thereof can serve as an even more relevant factor in the injury (and recovery) process. This means that all of their complicated muscle kinesiology descriptions and tests may be entirely irrelevant. The tricky part is that we currently have no way of determining exactly what the cause of anything but the most traumatic contact or impact injuries is. Much the same is true about chronic pain. In plain words, anyone who claims otherwise, is not telling you the whole truth.

The Use of Muscle and Joint Action Tables

All of those detailed muscle action tables that many of us rely upon now and again should emphasize that it is preferable to think about joint actions rather than muscle actions when one is analysing which muscles are involved in producing a given movement or if one is trying to ascertain which muscles are trained on a specific machine.

The popular practice of identifying only the "prime movers," as happens in most popular weight-training or bodybuilding publications, offers a partial and misleading view of the situation, especially as the stabilizers may be contracting far more vigorously than the movers during some exercises.³ There is no situation in which stabilizers are not also contracting while the movers are carrying out their dynamic role. Similarly, it is misleading and incorrect to rigidly classify muscles as being solely "tonic" or solely "phasic" in all situations, as is done by workers such as Janda. Thus, in analyzing any movement, one should always identify:

• which joints are being moved
• which joints are being stabilized
• which joints are being stabilized and moved concurrently.

Then the relevant muscles involved in any moving and stabilizing tasks may be determined by consulting the appropriate muscle or joint action tables. Even then, this still offers an incomplete view of the mechanics of human movement, because this approach tends to proliferate the popular, but erroneous view that:

• the same movement is always produced by the same muscles
• the same muscles always produce the same movement
• the same muscles are dominant throughout the full range of movement
• muscles only act as active tissues
• muscles only act as movers or stabilizers
• muscles are the only important tissues which control movement

As has been noted by many, to identify which muscles are active during any movement, the average personal trainer need not necessarily use an EMG (electromyograph), unless the objective is more accurate research. Instead, skilled, firm palpation with the fingers over appropriate surface areas of the body will provide an approximate working knowledge of which muscles or other tissues seem to be involved. These may be checked by referring to any anatomical chart, as long as the limitations which I have mentioned earlier in this article are borne in mind. Though sensitive palpation can identify approximate regions of maximum and minimum muscle tension, the more accurate degree to which each muscle group is involved at any given stage of a movement has to be determined by means of an EMG or a myotensiometer, which I have used to examine the relationship between joint torque and corresponding changes in muscle tension (Siff, 1986). However, as noted before, it is not possible to accurately assess the action of each muscle

This type of testing confirms that it is misleading and inaccurate to refer to muscle isolation exercises, because the degree of isolation (or dominant involvement) of a single muscle group depends on how large the resistance is (Supertraining, Ch 4). In general, the greater the load, the greater the overflow and the greater the involvement of other muscle groups. Unfortunately, this facilitatory or compensatory involvement of other muscles is far too often regarded as a sure sign of “imbalance” or pathology, whereas it may well be that this pattern of co-activation may be perfectly normal for that person under those conditions. Moreover, it is invalid to assume that any such compensatory or adjunct muscle action measured clinically under static or slow conditions also takes place in far more dynamic multi-articular sporting actions or daily life.

Others like Janda rely on hypotheses about functional muscle imbalances to maintain that "tight" or "overactive" muscles should be relaxed or stretched before initiating a strengthening routine or else the muscle imbalance will only be reinforced. How a muscle can possibly be "overactive" is anyone's guess, unless one assumes that the muscle is in a state of unrelenting spasm. Even then, this does not represent "overactivity"; rather, it refers to unproductive, nonspecific or “spurious” muscle action which results in no "functional" movement - and its origins may lie in the nonlinear, random or chaotic nature of many biological processes, as was discussed near the beginning of this article.

Some further remarks are warranted here. Lest one be tempted to consider that the muscles alone are responsible for all stabilization and mobilization, we must remember that ligaments, fasciae and joint capsules play an important role in passively stabilizing some joints to enable the body to actively use the muscles to execute other tasks. Although this stabilizing role is well known in preventing joint damage when loading threatens to move a joint beyond its active structural limits, these soft tissues also play a vital role during non-emergency situations.

Limitations of Anatomical Movement Analysis

Standard anatomical textbook approaches describing the action of certain muscle groups in controlling isolated joint actions, such as flexion, extension and rotation, frequently are used to identify which muscles should be trained to enhance performance in sport. Virtually every bodybuilding and sports training publication invokes this approach in describing how a given exercise or machine ‘works’ a given muscle group, as do most of the clinical texts on muscle testing and rehabilitation.

The appropriateness of this tradition, however, recently has been questioned on the basis of biomechanical analysis of multi-articular joint actions (Zajac & Gordon, 1989). This classical method of functional anatomy defines a given muscle, for instance, as a flexor or extensor, on the basis of the torque that it produces around a single joint, but the nature of the body as a linked system of many joints means that muscles which do not span other joints can still produce acceleration about those joints.

The anatomical approach implies that complex multi-articular movement is simply the linear superimposition of the actions of the individual joints which are involved in that movement. However, the mechanical systems of the body are nonlinear and superposition does not apply, since there is no simple relationship between velocity, angle and torque about a single joint in a complex sporting movement. Besides the fact that a single muscle group can simultaneously perform several different stabilizing and moving actions about one joint, there is also a fundamental difference between the dynamics of single and multiple joint movements, namely that forces on one segment can be caused by motion of other segments. In the case of uniarticular muscles or even biarticular muscles (like the biceps or triceps), where only one of the joints is constrained to move, the standard approach is acceptable, but not if several joints are free to move concurrently.

Because joint acceleration and individual joint torque are linearly related, Zajac and Gordon (1989) consider it more accurate to rephrase a statement such as “muscle X flexes joint A” as “muscle X acts to accelerate joint A into flexion.” Superficially, this may seem a matter of trivial semantics, but the fact that muscles certainly do act to accelerate all joints has profound implications for the analysis of movement. For instance, muscles which cross the ankle joint can extend and flex the knee joint much more than they do the ankle.

Biomechanical analysis reveals that multiarticular muscles may even accelerate a spanned joint in a direction opposite to that of the joint to which it is applying torque.

In the apparently simple action of standing, soleus, usually labelled as an extensor of the ankle, accelerates the knee (which it does not span) into extension (Fig 1) twice as much as it acts to accelerate the ankle (which it spans) into extension for positions near upright posture (Zajac & Gordon, 1989).

In work derived from Lombard’s Paradox ("Antagonist muscles can act in the same contraction mode as their agonists"), Andrews (1985, 1987) found that the rectus femoris of the quadriceps and all the hamstrings act in three different ways during cycling, emphasizing that biarticular muscles are considered enigmatic. This paradox originally became apparent when it was noticed that in actions such as cycling and squatting, extension of the knee and the hip occurs simultaneously, so that the quadriceps and hamstrings are both operating concentrically at the same time. Theoretically, according to the concept of concurrent muscle antagonism, the hamstrings should contract eccentrically while the quadriceps are contracting concentrically, and vice versa, since they are regarded as opposing muscles.

Others have shown that a muscle which is capable of carrying out several different joint actions, does not necessarily do so in every movement (Andrews, 1982, 1985). For instance, gluteus maximus, which can extend and abduct the hip, will not necessarily accelerate the hip simultaneously into extension and abduction, but its extensor torque may even accelerate the hip into adduction (Mansour & Pereira, 1987).

Gastrocnemius, which is generally recognized as a flexor of the knee and an extensor of the ankle, actually can carry out the following complex tasks (see Fig 2):

1. flex the knee and extend the ankle
2. flex the knee and flex the ankle
3. extend the knee and extend the ankle

During the standing press, which used to be part of Olympic Weightlifting, the back bending action of the trunk is due not only to a Newton III reaction to the overhead pressing action, but also due to acceleration caused by the thrusting backwards of the triceps muscle which crosses the shoulder joint, as well as the elbow joint. This same action of the triceps also occurs during several gymnastic moves on the parallel, horizontal and uneven bars. This back extending action of the triceps is counteracted by the expected trunk flexing action of rectus abdominis and the hip extension action of the hip flexors, accompanied by acceleration of the trunk by the hip flexors.

Appreciation of this frequently ignored type of action by many multiarticular muscles enables us to select and use resistance training exercises far more effectively to meet an athlete’s specific sporting needs and to offer superior rehabilitation of the injured athlete.

Conclusion

Because of this multiplicity of actions associated with multiarticular complex movement, Zajac and Gordon stress a point made by Basmajian (1978), namely that it may be more useful to examine muscle action in terms of synergism rather than agonism and antagonism. This is especially important, since a generalized approach to understanding human movement on the basis of breaking down all movement into a series of single joint actions fails to take into account that muscle action is task dependent.

In conclusion, some words need to be said about how muscle actions are controlled in movement and stabilization because recent research is also questioning the traditional views about how proprioception is involved in such processes. From work by Dr Melzack, one of the pre-eminent researchers into the mechanisms of pain, it seems that the neural networks for perceiving the body and its parts are built into the brain, so that various therapies based upon the effects of sensory proprioception on posture, muscle 'tightness', muscle imbalance, movement and pain may be based upon very shaky grounds. This is what the he concludes from his studies on ‘phantom limb’ pain and what its implications are for understanding motor control:

"The phenomenon of phantom limbs is more than a challenge to medical management. It raises doubts about some fundamental assumptions in psychology. One such assumption is that sensations are produced only by stimuli and that perceptions in the absence of stimuli are psychologically abnormal. Yet phantom limbs, as well as phantom seeing and hearing, indicate this notion is wrong. The brain does more than detect and analyze inputs; it generates perceptual experience even when no external inputs occur. We do not need a body to feel a body. In short, phantom limbs are a mystery only if we assume the body sends sensory messages to a passively receiving brain. Phantoms become comprehensible once we recognize that the brain generates the experience of the body. Sensory inputs merely modulate that experience; they do not directly cause it." Indeed, how the muscles are involved and controlled in the myriad of daily and sporting activities can only make us sit back in wondrous appreciation of how limited our current state of knowledge is about our miraculous bodies and how important it is for us not to be too dogmatic about we think we understand.

References

1. Basmajian J Muscles Alive, 1978
2. Siff MC Supertraining Denver USA 2000
3. Archives of Supertraining Educational Forum: http://groups.yahoo.com/group/Supertraining