If many therapists and fitness professionals are to be believed, then our bodies are chronically in a sorry state of imbalance in modern society and especially in sport. All too often they proclaim that you have to be “tested” and “corrected” before you will ever become any form of competent athlete.
Many of you will have read or heard that your periodic injuries and less than exemplary performance in your favourite sport are due to the fact that there is some critical imbalance in the strength of your agonists and antagonists, various differences in strength between phasic or tonic muscles, detrimental deviations from some hypothetical “ideal” posture or movement pattern, or different strength ratios between muscles on opposite sides of your body.
Why are such claims being made? Well, for a start, research using isokinetic dynamometers (like Cybex™, KinCom™ and MedX™) appeared to show that, unless you displayed specific ratios between the flexors and extensors of the knees (mainly the hamstrings vs the quadriceps), you probably would have a higher incidence of knee injury. Other non-quantitative manual testing by muscle testing pioneers from the world of physiotherapy (such as the ageless Florence Kendall) also seemed to reveal the existence of perceived weaknesses or imbalances in muscles under specific types of testing using the hands to resist the limbs in prescribed patterns of movement or holding.
Subsequent research showed that the isokinetic tests were not as valid as was originally contended and that knee injuries were not more prevalent if the “golden ratio” of knee extensor-flexor strength was deviated from, or if there were differences as large as 15 percent between left and right leg strength in similar actions. The methods of manual testing also came in for considerable criticism because of their highly subjective and non-quantitative nature and their exclusive focus on single joint action, which happens quite seldom in our daily and sporting lives.
Methods of Testing
Before we go any further, let’s quickly summarise the major methods of muscle testing or analysis. These are:
- Manual muscle testing
- Isokinetic testing
- Isometric testing
- Other dynamometric testing (force plates and hand held)
- EMG (electromyographic) analysis
- Functional MRI (magnetic resonance imaging) - fMRI
- High speed video motion analysis
All of the above methods, except the last two, rely on indirect methods of analysing muscle action because they actually test the ‘strength’ of muscles in carrying out specific joint actions. What they really are doing is measuring the torque or moment produced by a joint in various static or dynamic actions.
In my earlier article on PTontheNet, entitled “So This is How The Muscles Work?” I discussed the background to the muscle testing in general. It is relevant to recap some of what I wrote there before I discuss some of the muscle testing methods in more detail.
There I noted that invasive electrodes to measure EMG from many muscles and MRI, as well high speed video and other biomechanical systems, therefore, are 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 methods of movement analysis and muscle testing are:
- They do not take into account the contributions to movement by distant muscles which do not cross the joints involved in the action.
- A given external movement pattern is not necessarily produced by the identical muscle actions everytime that the movement takes place (this issue was also discussed by top Russian scientist, Dr Bernstein, and in a recent copy of the Scientific American)
- 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 therapists 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) 3 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.
The appropriateness of isolated muscle testing by any means recently has been questioned on the basis of biomechanical analysis of multi-articular joint actions. 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 stabilising 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....
Others have shown that a muscle which is capable of carrying out several different joint actions, does not necessarily do so in every movement. 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.
Of all of the above methods listed earlier, only manual testing is subjective, non-quantitative and influenced by the actions and preconceptions of the therapist, so, not surprisingly it is not accepted as a valid method for scientific research of muscle action. If it is used therapeutically, the thorough worker will use one or more of the other tests to corroborate and extend the initial subjective perception of any muscle weakness or imbalance. Unfortunately, these limitations of manual testing are often ignored by many therapists, especially since their great pioneer, Florence Kendall, has been such a visible and charismatic promoter of their value and apparent ease of accurate application. Moreover, the additional time needed, limited availability, greater user training and cost of using other methods often deters one from using them.
In addition, manual testing, like many other methods of testing, has very limited value outside the clinical setting because it focuses on isolated joint action, which very rarely, if ever, happens in real life activities, especially under ballistic conditions (which occur in most or all sports). The inability of muscle testing to test muscle strengths and weaknesses during explosive and ballistic movement which play a major role in enhancing the efficiency of many human movements constitutes a major deficit in manual testing. There is no proof whatsoever that muscle weaknesses detected during isometric or slow conditions in a single testing plane of action necessarily will occur in real-life movements, particularly in sport.
The use of manual testing neglects the vital fact that muscle action on its own is only part of the process of producing motor output. Its use under the static or slow controlled movements against a tester’s hands is based upon the assumption that all muscle strength involves muscle cocontraction, or the concurrent ongoing involvement of agonistic and antagonistic muscle actions throughout the whole range of movement. This neglects another essential way in which the muscles produce movement, namely the use of ballistic action, in which the “agonist” launches the limb into action like a ballistic missile via a powerful initial thrust and then withdraws from the picture until the closing stages of the movement when the “antagonist” rapidly comes into play to halt or even reverse the movement. This sort of action is used whenever one runs, kicks, throws, strikes or otherwise has to produce a very rapid movement.
Moreover, a great deal of isolated joint testing considers compensatory and overflow muscle action to be undesirable or even pathological, which neglects the fact that the body can implement several different muscle strategies to solve any given motor problem. The work of the renowned late Dr Bernstein is especially relevant in this regard.
Attempts have been made to make manual testing more quantitative and acceptable by having the therapist hold small hand-held dynamometers (force measuring devices) against the limb being tested to measure the force produced in a given action. Unfortunately, it has been found that the accuracy of this method can be drastically diminished by the pressure being exerted by the therapist while holding the device against the limb.
Another manual method, which has nothing really to do with directly testing the muscles for the sake of assessing the force of muscles, is called “applied kinesiology” which presumes to test limb action to determine organic dysfunction, food sensitivities or illness in remote parts of the body.
The use of AK (Applied Kinesiological) testing has never been shown scientifically to offer any valid information on the functioning of internal systems, as is often claimed by its proponents. The following web article provides a thorough critique of AK: http://www.chirobase.org/06DD/ak.html
Applied Kinesiology [excerpts provided], Stephen Barrett, M.D.
Applied Kinesiology (AK) is a pseudoscientific system of muscle-testing and therapy. It was initiated in 1964 by George J Goodheart, Jr., D.C., and has become quite elaborate. Its basic notion is that every organ dysfunction is accompanied by a specific muscle weakness, which enables diseases to be diagnosed through muscle-testing procedures....
Note: Applied kinesiology should be distinguished from kinesiology (biomechanics), which is the scientific study of movement.
AK proponents claim that nutritional deficiencies, allergies and other adverse reactions to foods or nutrients can be detected by having the patient chew or suck on them or by placing them on the tongue so that the patient salivates. Some practitioners advise that the test material merely be held in the patient's hand or placed on another part of the body. A few even perform "surrogate testing" in which the arm strength of a parent is tested to determine problems in a child held by the parent......
Many muscle-testing proponents assert that nutrients tested in these various ways will have an immediate effect: "good" substances will make specific muscles stronger, whereas "bad" substances will cause weaknesses that "indicate trouble with the organ or other tissue on the same nerve, vascular, nutrition, etc., grouping.".......
Finding a "weak" muscle supposedly enables the practitioner to pinpoint illness in the corresponding internal organs in the body. For example, a weak muscle in the chest might indicate a liver problem, and a weak muscle near the groin might indicate "adrenal insufficiency.".......
Testing is also claimed to indicate which nutrients are deficient. If a weak muscle becomes stronger after a nutrient (or a food high in the nutrient) is chewed, that supposedly indicates "a deficiency normally associated with that muscle." Some practitioners contend that muscle-testing can also help diagnose allergies,and other adverse reactions to foods. According to this theory, when a muscle tests "weak," the provocative substance is bad for the patient. AK "treatment" may include special diets, food supplements, acupressure (finger pressure on various parts of the body), and spinal manipulation.
Goodheart states that AK techniques can also be used to evaluate nerve, vascular, and lymphatic systems; the body's nutritional state; the flow of "energy" along "acupuncture meridians"; and "cerebro spinal fluid function.".......
A great deal of muscle testing and rehabilitation after injury is based on the use of isokinetic dynamometers such as Cybex and KinCom. Inadequate performance and injuries are attributed to differences in strength between interacting muscle groups as determined isokinetically. Athletes are claimed to be training scientifically if they are tested regularly under isokinetic conditions. Research evaluating the effectiveness of training regimes is almost invariably based on isokinetic measurement and often the reputation of their authors means that the validity of this work is rarely doubted. However, is any extensive reliance on isokinetic measurement and rehabilitation warranted?
Fundamental Biomechanics of Isokinetic Devices
The faulty basic assumption is that isokinetic dynamometers are accurately constant angular velocity devices. The laws of physics deem it impossible to construct any machine which offers purely isokinetic resistance from beginning to end of motion. When a body is at rest, it has to be accelerated to reach a certain terminal velocity that can be maintained for a given period of time before it has to be decelerated to return to rest once more. This means that there is always a period of positive or negative acceleration associated with all movement, isokinetic or otherwise. The best that manufacturers of isokinetic devices can do is to minimise the duration of these phases, although they can never entirely eliminate them. To produce entirely isokinetic conditions from beginning to end of motion would necessitate the production of infinite acceleration, which contradicts the laws of science.
Justifiably, it might be asked if the existence of non-isokinetic measuring phases on these machines is important. This fact is vitally important, because most injuries occur during these transition phases when a limb is changing its velocity or tension is changing in the musculotendinous system and isokinetic testing can reveal no useful information about what is happening to the muscles then. A most serious problem is that isokinetic testing, like manual testing, can give no information on the major contribution played by the storage and release of elastic energy in the soft tissues during dynamic, natural actions such as walking, running, jumping or throwing. Stated simply, isokinetic testing or training is “nonfunctional.”
Biomechanical analysis of the force-time and rate of force development (RFD) curves for resisted free movement confirm the existence of vital muscular performance qualities such as maximal strength, starting strength (at the beginning of a movement), acceleration strength (while the movement is speeding up to maximum velocity) and explosive strength (see my first two articles on PtontheNet). The curves obtained isokinetically are so radically different from their free movement equivalents that they are of minimal value either for functional analysis or specific neuromuscular conditioning.
Recommended Strength Ratios
It is often claimed that the optimal ratio of quadriceps to hamstring strength is 60:40, but Russian scientists have found that this ratio depends on the specific type of sport. For example, they have determined that this ratio (measured when knee extension torque is greatest) should be nearer 80:20 for weightlifters and jumpers. Moreover, if the ratio is measured during movement on a treadmill, the ratio for runners is approximately 50:50. Despite these findings, the traditional 60:40 recommendation is widely accepted and much rehabilitation is based on restoring this ratio. Another popular belief is that injuries are far more common if the difference in strength between left and right lower extremities is more than 10 percent.
Recent research, however, has shown that neither of these recommendations is supported by scientifically controlled experiments which correct torque outputs for the effect of gravity and avoid stretching the hamstrings. In addition, the recommendation of a specific flexor/extensor ratio is vague, because this ratio varies throughout the range of joint motion, as may be seen in Figure 2.
Figure 2. Research showing how the ratio of quadriceps to hamstring strength (torque) changes with knee angle and velocity of joint movement.
For example, the ratio for the knee at 80o is about 75:25 at 36 degs/sec, whereas it is 68:32 at 180 degs/sec. The only stage at which the ratio is 60:40 occurs at an angle of approximately 50o. Not only does the ratio change with joint angle, but it also changes with velocity of measurement, so it is meaningless to prescribe an optimal ratio for any joint. It would be more relevant to refer to a characteristic curve over a full range of movement for a given angular velocity.
Isokinetic testing of a subject with an injured right knee (see Figure 3). Paradoxically, the injured shows much the same strength as the uninjured left leg under concentric conditions, but tests significantly stronger than the uninjured leg under eccentric conditions. This result, which is exactly the opposite of what the tests would be expected to show, emphasizes that even quantitative testing can be very misleading.
Another confounding factor is the influence of the angle of nearby joints on the torque that is produced by given muscles about the joint in question. For instance, knee extension torque increases with hip angle, a phenomenon that is of immense practical importance to weightlifters, jumpers and sprinters, in particular. These athletes are well aware of operating over optimal ranges of relative knee and hip angle. Measurement of the relative disposition of these angles forms the basis of the cyclogram used by biomechanists to study gait efficiency. Therapists attempt to solve this problem by immobilising the seated athlete's hips by using strong inextensible straps across the upper thighs. This immediately creates non-functional conditions for evaluating the biomechanics of knee extension/flexion in free space.
The seated posture produces highly constrained and accurate conditions for measuring torque that is specific to the seated posture and not to the posture exhibited during any actual sporting action.
Furthermore, seated isokinetic evaluation of knee motion is usually imprecisely controlled, since it is rarely combined with electromyography or myotonometry (muscle tension measurement) to ascertain the relative contributions made to joint torque by the different muscles comprising the quadriceps and hamstrings. Prescription of any exercise regime without knowing precisely which muscles are involved is just as haphazard with or without the aid of costly isokinetic devices. What complicates matters further is that the degree of lateral or medial rotation of the lower extremity has a significant effect on the relative involvement of vastus medialis and lateralis, so that this variable also needs to be more accurately controlled if isokinetic testing is to become scientifically rigorous. Open-chain testing of the lower extremity with the sole of the foot not in contact with the ground alters the way in which popliteus initiates knee flexion or gastrocnemius contributes to knee flexion, two actions that are of great importance in running, lifting or jumping.
In addition, seated testing does not take into consideration medial rotation of the knee by sartorius, gracilis, semimembranosus or semitendinosus, or lateral rotation by biceps femoris. The role of these muscles in performance may be largely ignored for the average client, but certainly not in the case of competitive athletes, who place maximal demands on their bodies.
The entire system of PNF is based on the importance of specific patterns of joint action and muscle recruitment in determining movement efficiency and safety, yet therapists with an extensive knowledge of PNF unquestioningly accept results produced under the highly unnatural conditions imposed by isokinetic machines or manual testing. They are fully aware that training in a given way produces specific neural changes which become part of the central nervous programme that determines all movement efficiency; they meticulously apply the precise kinesiological patterns prescribed by Knott and Voss, but they are compelled to ignore this knowledge when using isokinetic machines.
Testing and Muscle Physiology
Some of the implications of muscle physiology are also relevant to understanding the limitations of manual and isokinetic testing:
- The initial muscular state preceding many sporting actions is intense isometric contraction or explosive isometric contraction accompanied by storage of elastic energy in the tendons. This state has a profound influence on explosive strength, metabolic efficiency and safety, yet all isokinetic testing or training involves insignificant initial levels of isometric contraction.
- The myotatic stretch reflex has great significance for increasing the working effect of concentric muscle action, with the greater the rate of stretch, the stronger this reflex. Most explosive movements in running, jumping, lifting and throwing rely on intense recruitment of this reflex, which is not possible under isokinetic conditions. In fact, the production of powerful, skillful movements in all sports relies on the establishment of precise neuromuscular patterns through integration of many different reflexes. The elimination of most of these reflex actions by isokinetic apparatus ensures that isokinetic testing and training is only of value during the early general conditioning or rehabilitation phase, but of no real significance during the specific preparation or competitive phases of sports training.
- Muscles generally interact to produce two kinds of action: cocontraction or ballistic movement. In cocontraction, agonists and antagonists contract simultaneously, with dominance of the former producing the external motion. Ballistic movement comprises bursts of agonist activity followed by phases of relaxation during which the motion continues due to stored limb momentum. Skilled, rapid ballistic and fast continuous movements are preprogrammed in the central nervous system (CNS) and rarely involve feedback during the action, whereas slower, discontinuous movements involve cocontraction and ongoing feedback to the CNS from the muscles and joints. Isokinetic conditions do not permit the production of ballistic or discontinuous cocontractive actions, so that they address only a few of the needs of sports testing and preparation.
- Some authorities maintain that strength is best developed if muscle tension is kept at a maximum throughout the movement by the use of isokinetics. This proposition is neither proved nor is it universally accepted with reference to all types of strength. Moreover, torque produced under isokinetic conditions is usually much lower than that produced isometrically at the same joint angle.
- If contraction of the agonists is preceded immediately by maximal contraction of the antagonists, the force produced by the agonists is increased, a phenomenon often called reciprocal inhibition and regularly used in PNF. Most isokinetic devices do not permit this type of motion, which commonly occurs during plyometric rebounding activity.
- The patterns of force production are different for bilateral (simultaneous use of both limbs) and unilateral (alternate use of each limb) sports, so that isokinetic comparisons of relative limb strength can be very misleading. Furthermore, each person has a dominant limb, so that functional asymmetry is perfectly normal. This does not imply that the dominant limb has superior strength; it often displays superiority in skill, especially in kicking, jumping and throwing sports. Yet, it is common to find therapists trying to strengthen the weaker kicking limb of a footballer isokinetically, although the support leg is meant to produce greater stabilising strength.
The convenience of isokinetic testing should be weighed against its high cost, limited application and the unsupported claims of manufacturers. The detailed review of the strengths and weaknesses of isokinetic methods given by Osternig provides further useful information in this regard.
Other Forms of Testing Surface
EMG may also be used to test muscle activity, but it carries with itself its own particular problems, such as the difficulty in applying it during vigorous activity or to deeper lying muscle tissue.
In addition a large number of electrides have to be attached to the different limbs and this type of analysis is beyond the capabilities of all but the most sophisticated clinicians and laboratories.
Although technological measurement is invaluable and highly desirable in sport and rehabilitation, oversimplification of any highly complex situation can lead to serious errors and hinder scientific progress. The simplistic central sun and planetary electron model of the atom was a valuable tool for early 20th century physicists, but its replacement by more sophisticated quantum models has advanced our understanding of the universe enormously. Unqualified reliance on a single manual testing or isokinetic model to assess muscular strength and endurance is tantamount to permanently accepting the early model of the atom, just because it is easy to work with. The fact is that human motion involving static and dynamic multiple link components is extremely complicated, and manual or isokinetic testing both can offer only a very simplistic way of obtaining information on a limited number of variables. Isokinetic machines are useful for measuring isokinetic actions and changes in two dimensions, just as isometric dynamometry is useful for measuring isometric strength at a given joint angle. Extrapolation of results obtained under these conditions to sporting actions involving other types of muscle contraction and patterns of movement is scientifically unacceptable and misleading. Human mobility and stability are the integrated result of the appropriate phases of isometric and non-isokinetic muscle contraction occurring with a specific timing in threedimensional space over specific ranges of joint angle.
Multi-faceted human movement demands the use of far more versatile and complex technological means, a type of kinesiological polygraph which integrates information yielded by concurrent use of devices such as high speed video, EMG, myotensiometers, accelerometers and force plates.
The ultimate measure of successful testing and training is unequivocal improvement in the athlete's performance, so that sporting movements should still be regarded as the final test of any training or rehabilitation regime.
- Andrews J G (1982) On the relationship between resultant joint torques and muscular activity Med Sci Sports Exerc 14: 361-367
- Andrews J G (1985) A general method for determining the functional role of a muscle J Biomech Eng 107: 348-353
- Basmajian J (1978) Muscles Alive Williams & Wilkins Co, Baltimore
- Knott M & Voss D (1977) Proprioceptive Neuromuscular Facilitation Balliere, Tindall & Cassell
- Osternig L R (1986) Isokinetic dynamometry: Implications for muscle testing and rehabilitation Exer & Sport Sci Rev 14:45-80
- Siff M C (1995) Limitations of Isokinetic Testing and Rehabilitation Proc of SA Sports Medicine
- Association Congress Durban, 22-24 March
- Siff M C (2000) Supertraining Supertraining Int Denver USA
- Siff M C (2002) Facts and Fallacies of Fitness Supertraining Int Denver USA
- Stephens D & Reid J (1988) Biomechanics of hamstring strains in sprinting events Canadian J of Sport Sciences 13(3): 78
- Supertraining Discussion Forum: Many articles on topics relating to balance testing and training appear on this website: http://groups.yahoo.com/group/Supertraining/
- Thistle H, Hislop H, Moffroid M et al (1967) Isokinetic contraction: a new concept of resistive exercise Arch of Physical Medicine & Rehabilitation 49: 279-282
- Vorobyev A (1978) A Textbook on Weightlifting International Weightlifting Federation, Budapest
- Zajac F E & Gordon M F (1989) Determining muscle’s force and action in multi-articular movement Exerc Sport Sci Revs 17: 187-230