Original article
Intraexaminer comparison of applied kinesiology manual muscle testing of varying durations: a pilot study

https://doi.org/10.1016/j.jcm.2009.12.005Get rights and content

Abstract

Objective

The purpose of this study is to investigate the difference in results (strong/facilitated vs weak/functionally inhibited) between short (1 second) and long (3 seconds) manual muscle tests (MMTs) on the same subject and to pilot the use of thin-film force transducers for characterizing the parameters of MMT and for measuring maximum voluntary isometric contraction (MVIC).

Method

Forty-four healthy chiropractic students were tested. A thin-film force transducer recorded force over time during MVIC of the middle deltoid and 1- and 3-second MMTs of the same subjects. The MMTs were graded as strong (able to resist the testing pressure) or weak (unable to resist testing pressure, breaking away).

Results

Forty-two short tests were strong, and 2 were weak. Thirty-nine long tests were strong, and 5 were weak. κ (0.54) showed fair agreement for results between short and long tests. Peak force in both short and long weak tests was higher than that in strong tests when expressed as a proportion of maximum contraction. All manual tests used less force than MVICs.

Conclusions

This study demonstrated that a study of this nature is feasible. Longer test durations demonstrate some muscle weaknesses that are not evident on 1-second MMTs. Thin-film transducers show promise for recording MMT parameters for research purposes.

Introduction

Applied kinesiologists test muscles before and after challenges and treatments, and may make clinical judgments based on immediate changes in muscle tests.1 Muscles are tested according to similar methods described by Kendall et al2 from a contracted position with pressure toward lengthening. If the subject can maintain the position against gradually increasing pressure, it is graded as “facilitated” or “strong” (grade 5). If the muscle weakens during the procedure, the muscle is rated as “inhibited” or “weak” (grade 4 or less). Applied kinesiology (AK) authors suggest that manual muscle testing (MMT) measures a complex proprioceptive response to changing pressure, rather than strength of the muscle itself.1, 3 The range of parameters that yield similar results on this binary evaluation is not currently known. This information is important in training accurate muscle testers and in evaluating the reliability and validity of other AK procedures based on muscle responses to various stimuli and challenges.

The physiotherapy literature distinguishes between “make” or “active strength” and “break” or “passive strength” testing both in MMT and in handheld dynamometry. In both styles, the muscle is tested relatively isometrically, either near its most shortened position or in the middle of its range of motion. In break testing, there is also eccentric lengthening as the muscle breaks away. Both differ from isokinetic testing, such as the Cybex,4 which tests the muscle through an entire range of motion at a constant speed.

Active or “make” tests are similar to maximum isometric voluntary contraction tests—the subject presses against a fixed dynamometer, a strap with a force transducer is used, or the examiner acts as a fixed point.4, 5 Given intact neurologic control, the subject's own initiative and muscle size determine the maximum force generated. In contrast, in break tests, the subject resists the examiner's increasing pressure until the muscle breaks away. This requires more complex proprioception than simply pressing against a fixed resistance. The subject must continually adjust muscular output to match the examiner's pressure. Breaking strength testing is frequently cited as yielding higher peak force measurements than make tests. If the breaking force of a muscle is to be measured with a dynamometer on each test, the examiner must be stronger than the subject.5 The key distinction between “make” and “break” in the physiotherapy literature is whether the resistance the tested muscle contracts against is constant at a fixed location or gradually increasing and mobile. This distinction might be purely academic except for the likelihood that the 2 styles to some degree monitor different aspects of neuromuscular control.

Comparison of the results of measures of muscle force under various conditions is complicated by the wide range in size and fitness between subjects. Therefore, it is useful to normalize results of dynamometry by comparison to maximum contraction for each subject.6 This has not been done in previous AK studies.

Maximum voluntary isometric contraction (MVIC) is tested, by definition, as a “make” or “active” contraction test. The subject pushes against a relatively stationary force-recording device that offers stable resistance. Methods for measuring MVIC are described in many studies. Some use strain gauges, and others have the subject press directly against some form of force transducer.7, 8, 9, 10

In a study of normative values for MVIC in healthy subjects, Meldrum et al11 describe the method for measuring MVIC. They summarize references comparing MVIC and MMT, concluding that, generally, MVIC shows better sensitivity than does MMT for small changes in quantitative muscle strength in the context of monitoring patients with neuromuscular disease. Manual muscle test grading on a 5-point numerical scale does not allow for the fine objective gradations that can be done when measuring units of force. A muscle may fall within one grade at a range of forces, so small interval changes may be missed. These concerns are important for evaluation of progress or deterioration in a patient in rehabilitation or with neuromuscular pathology. Maximum voluntary isometric contraction testing is appropriate to test the size of the muscle itself or the changes in muscle in neurologic disease or recovery. It is equipment intensive and not easily adapted to clinical practice or to measuring rapid changes in muscle function over the short term.

On especially strong muscles and for weaker testers, it is possible that clinicians may miss small short-term changes in strength with AK MMT as well.

Schmitt12 observed that subtle differences in timing seemed to yield different results in AK MMT. He described a “doctor-initiated” test in which the subject is asked to resist the doctor's gradually increasing force. “Patient-initiated” testing begins in the same position, but the patient is asked to push against the examiner's hand as hard as possible. This test style usually includes verbal encouragement to continue to push. In both tests, the examiner attempts to break the patient's contraction, the difference being timing. Schmitt postulated that the timing differences accessed different neurologic pathways. This model is similar but not identical to the make/break contrast.

Conable et al13 were unable to demonstrate a consistent difference in whether the patient's or the examiner's muscle contraction began first when 41 experienced AK testers attempted to perform both patient-started and doctor-started muscle tests of the middle deltoid. This study found that the mean duration of AK muscle testing was 1.3 seconds (range, .325-3.5 seconds). There was a suggestion of a bimodal distribution of durations above and below about 1.5 seconds as examiners attempted to execute different styles of muscle tests. This led to the question of whether the difference Schmitt observed was a matter of duration rather than whose contraction began first.

This is important in that at least one study that purports to compare reliability of these 2 styles of muscle testing did not report duration. Hsieh and Phillips14 did a reliability study with a computerized dynamometer comparing doctor-initiated and patient-initiated testing of 3 muscles by 3 testers over 2 sessions on 2 separate groups of 15 subjects. The authors concluded that patient-initiated testing was more reliable than doctor-initiated testing with this instrument. However, when the details of this study are examined, problems with this conclusion are revealed. Only peak force was recorded, rather than a continuous recording of force over time, making it impossible to determine the actual timing of each method. Because the examiners were free to stop the “doctor-initiated” test whenever they were satisfied that the muscle had “locked” or “broken away,” it is unsurprising that these tests demonstrated quite a wide variation in peak force. The “patient-initiated” tests required the examiner to maintain pressure until an apparent maximum was achieved. It seems likely that this point would be more similar tester to tester and test to test. Subjects were tested by one or the other style of testing, not both, making comparison between styles problematic. This illustrates the need to better define the parameters of muscle tests used in AK research.

Manual muscle testing in AK clinical practice uses direct hand contact with the subject. The interposition of an instrument for research alters the quality of the muscle test and the delicacy of the examiner's perception. The present study piloted the use of a thin-film force transducer to record MMT. Similar sensors have been used in research on prosthetics, ergonomics, and physical medicine.15, 16

This study compared results (strong/weak) between short (1 second) and long (3 seconds) MMTs of the same subject. The null hypothesis was good agreement between long- and short-duration muscle tests, in other words, that the duration of the test would not influence the outcome. The research hypothesis is that the 2 conditions are at least partially independent of each other and so would demonstrate a low κ.

Secondarily, this study compared peak force of the MVIC tests between strong and weak tests and peak force of MMTs between strong and weak tests in absolute terms and as a percentage of estimated maximum voluntary contraction to further define the objective differences between the states applied kinesiologists refer to as “strong” and “weak.”

Section snippets

Methods

The author, an applied kinesiologist with more than 30 years in the practice and teaching of AK, examined 44 chiropractic students (23 men, 21 women) with a mean age of 26 years (range, 20-54). Subjects were screened for major injuries or physical conditions preventing testing the middle deltoid. No volunteers were excluded. Informed consent was obtained before testing. The study was approved by the Institutional Review Board of Logan College of Chiropractic and the Human Research Ethics

Results

Force results represent a fraction of the total force exerted by the patient, as the sensor only registered a part of the contact area of the strap for MVIC and a part of the examiner's hand contact for muscle testing.

As seen in Table 1, maximum contraction tests averaged 7.16 seconds. Short tests averaged 1.09 seconds. The intended duration for the long condition was 3 seconds; however, long tests averaged only 2.34 seconds. Long tests averaged significantly higher peak force than short tests

Discussion

Some muscles that can hold an isometric contraction in an MMT for a short time cannot maintain the contraction for the 2.5 to 3 seconds of a longer test. Short and long MMTs sometimes yield different results. Because many AK examiners use tests of 1 second or less in practice,18 muscle weaknesses that develop later may be missed.

It is possible that the differences observed by Schmitt12 between “patient-started” and “examiner-started” tests may well be differences in duration of tests. Schmitt

Conclusion

Applied kinesiology muscle testing uses submaximal forces and measures neuromuscular response to gradually increasing pressure, rather than total force that the muscle is capable of generating. Longer tests may demonstrate weakness that is not evident when the muscle is tested for 1 second. Duration of tests should be controlled for and specified in future AK research, particularly when testing before and after diagnostic or therapeutic interventions and challenges. Thin-film Flexiforce force

Funding sources and conflicts of interest

No outside funding was received for this project.

The costs for sensors and the custom interface were paid personally by the author. The author teaches applied kinesiology at Logan College of Chiropractic, is a Certified Teaching Diplomate of the International College of Applied Kinesiology, and serves on the International Board of Standards and the International Board of Examiners of the International College of Applied Kinesiology.

Acknowledgment

This project was part of a master's degree program through RMIT University in Australia. The author thanks her RMIT advisor, Dr Max Walsh, and Logan College of Chiropractic Research Division for the use of their space, equipment, and work-study students during data collection. The author also thanks Dr Quinggen Zhang for his help and advice in developing the instrumentation.

References (21)

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