Effect of instructions to simulate a back injury on torque reproducibility in an isometric lumbar extension task

Critical issues in the use of muscle testing for the determination of sincerity of effort

Over the past 20 years, there have been numerous attempts to identify methodologies that are capable of the determination of sincerity of effort during muscle testing. The ensuing paper reviewed this literature and drew several conclusions. Injured patients and healthy volunteers do produce less force and more variable force while performing submaximal contractions than maximal contractions. However, submaximal efforts during strength testing can be reproduced and the use of force variability is not adequate to distinguish sincerity of effort. Visual examination of the shape of force output curves is also not adequate for distinguishing sincerity of effort. Furthermore, much of the research using strength ratios, difference scores, and an assortment of different parameters derived during strength testing has not established reliable and clinically useful methods of differentiating effort levels. Methods examining motion variability, radial/ulnar force output ratios, difference scores of eccentric-concentric ratios, and electromyography offer some promise, but numerous critical issues need to addressed. The use of the coefficient of variation, for example, is statistically untenable given the number of trials appropriate for clinical samples. Several studies have inadequate sample size to number of variable ratios. Many studies have questionable or at least unknown generalizability to patient samples and actual functional capacity. It is critical that other explanatory variables such as fear of injury, pain, medications, work satisfaction, and other motivational factors be considered. It is our opinion that there is not sufficient empirical evidence to support the clinical application of muscle testing to determine sincerity of effort.

Impairment magnification during dynamic trunk motions

STUDY DESIGN

An examination of a group of patients with low back disorder and a group of healthy (asymptomatic) individuals asked to produce trunk motions under sincere and insincere experimental conditions. Trunk motion components were examined to determine which combination of motion components could best distinguish between sincere and insincere efforts.

OBJECTIVE

To determine whether examination of trunk motion components could be used to identify impairment magnification during unresisted repeated bending tasks.

SUMMARY OF BACKGROUND DATA

Trunk motion measures can be used to assess and "benchmark" the status of the low back. However, these measures typically are clinically useful only if the individual is producing an effort that does not magnify the impairment during the functional evaluation. This study addressed the issue of impairment magnification during the production of free dynamic trunk motion.

METHODS

The trunk motion characteristics of 100 healthy individuals and 100 patients with chronic low back disorders were documented. All participants were asked to produce the trunk motions in two different types of conditions. In the one experimental condition, they were asked to produce sincere trunk motions. In the other experimental condition they were asked to pretend either that they were experiencing low back pain (the asymptomatic group) or that their pain was worse than it actually was (group with low back pain).

RESULTS

A combination of trunk motion measures was able to distinguish well between the conditions. Sensitivity and specificity for the asymptomatic group were 92%, whereas they were 75% for the group with low back pain. Overall, sensitivity and specificity were 81.5% for all the participants combined.

CONCLUSIONS

These results indicate that motion measures can be used to help assess impairment magnification during functional trunk motion testing. These measures can provide a means by which to scrutinize the quality of quantitative measures indicating the extent of a low back disorder. These objective motion measures also can be used to complement other subjective observational methods for the assessment of impairment.

Chronic pain disability exaggeration/malingering and submaximal effort research

OBJECTIVE

This is the first review of chronic pain (CP) malingering/disease simulation research. The purpose of this review was to determine the prevalence of malingering within CP patients (CPPs), whether evidence exists that malingering can be detected within CPPs, and to suggest some avenues of research for this topic.

DESIGN

A computer and manual literature search produced 328 references related to malingering, disease simulation, dissimulation, symptom magnification syndrome, and submaximal effort. Of these, 68 related to one of these topics and to pain. The references were reviewed in detail, sorted into 12 topic areas, and placed into tabular form. These 12 topic areas addressed the following: existence of malingering within the CP setting; dissimulation, identification simulated (faked) facial expressions of pain; identification of malingering by questionnaire; identification of malingered sensory impairment; identification of malingered loss of hand grip strength; identification of submaximal effort by isometric strength testing; identification of submaximal or malingered effort by isokinetic strength testing; identification of submaximal or malingered effort by the method of coefficient of variation; self-deception; symptom magnification syndrome; and miscellaneous malingering identification studies. Each report, in each topic area, was rated for scientific quality according to guidelines developed by the Agency for Health Care, Policy and Research (AHCPR) for rating the level of evidence presented in the reviewed study. The AHCPR guidelines were then used to rate the strength and consistency of the research evidence in each topic area based on the type of evidence the reports represented. All review conclusions were based on the results of these ratings.

SETTING

Any medical setting reporting on either malingering or disease simulation, or dissimulation, or submaximal effort and pain.

PATIENTS

Normal volunteers, CPPs, or any group asked to produce a submaximal or malingered effort or a malingered test profile.

RESULTS

The reviewed studies indicated that malingering and dissimulation do occur within the CP setting. Malingering may be present in 1.25-10.4% of CPPs. However, because of poor study quality, these prevalence percentages are not reliable. The study evidence also indicated that malingering cannot be reliably identified by facial expression testing, questionnaire, sensory testing, or clinical examination. There was no acceptable scientific information on symptom magnification syndrome. Hand grip testing using the Jamar dynamometer and other types of isometric strength testing did not reliably discriminate between a submaximal/malingering effort and a maximal/best effort. However, isokinetic strength testing appeared to have potential for discriminating between maximal and submaximal effort and between best and malingered efforts. Repetitive testing with the coefficient of variation was not a reliable method for discriminating a real/best effort from a malingered effort.

CONCLUSIONS

Current data on the prevalence of malingering within CPPs is not consistent, and no conclusions can be drawn from these data. As yet, there is no reliable method for detecting malingering within CPPs, although isokinetic testing shows promise. Claims by professionals that such a determination can be made should be viewed with caution.

Detection of a "faked" strength task effort in volunteers using a computerized exercise testing system

The objective of this study was to develop an experimental method to separate a "faked" strength effort from a "best" effort in volunteers. Thirty-four pain-free volunteers (18 males, 16 females) performed a shoulder press and pull-down on an isokinetic computerized exercise testing system (CETS), giving a best effort followed by a faked effort. Two months later, a randomly selected subgroup (6 males) repeated the experiment to test the predictive validity of the derived variables. In the statistical analysis, best efforts were first compared with fake efforts by paired ttest for 80 CETS variables for males and females separately. Variables showing a strong difference between the best and faked effort were then selected for further analysis. In the second step of the analysis, the method of multiple correlations (r2 method) was used to reduce the number of redundant CETS variables to five in both the male and female groups. In the third step, a stepwise discriminant analysis was used to select predictor variables for the male and female groups. For the variables selected by the discriminant analysis for both males and females, sensitivities and specificities were calculated. Finally, the developed discriminant formula was used in the predictive validity part of the study to determine the sensitivities and specificities of the developed method. The discriminant analysis selected the following CETS variables for male and female groups, respectively: duty cycle down, work weight/down, peak value up (males); and average power up, 40% repetition down, duty cycle up (females). For males, using their three variables, the discriminant function classified 77.14% of the efforts correctly with 88.9% sensitivity and 64.7% specificity. For females, using their three variables, the discriminant function classified 90.63% of the efforts correctly with 100% sensitivity and 81.3% specificity. In the predictive validity group, the discriminant function classified 75% of the efforts correctly with 83.3% sensitivity and 66.7% specificity. This pilot study indicates that the method developed here may be useful in the experimental study for the discrimination between faked and best efforts on this isokinetic CETS machine. Future studies using this method will need to involve a larger number of volunteers.

Identifying submaximal muscular effort: reliability of difference scores calculated from isometric and isokinetic measurements

The present investigation examined the reliability of a derived strength measurement and also how variability between test sessions affects the utility of this variable for judging an individual's muscular effort. 31 young healthy men (M age = 25 yr.) completed three isometric and isokinetic concentric contractions of the knee extensors, using maximal and self-selected submaximal efforts, on each of two test sessions. Difference scores between isometric and isokinetic measurements were calculated by subtracting the mean of the three isokinetic peak torques from the mean of the three isometric peak torques for each individual subject for maximal and submaximal efforts performed on both test sessions. For the group of subjects, difference scores were significantly greater during maximal (33 +/- 29 Nm) than submaximal (13 +/- 30 Nm) efforts, suggesting subjects could not maintain the same relationship between isometric and isokinetic muscular actions across the maximal and submaximal conditions. However, the test-retest reliability of the difference scores was only modest even when data were averaged over two test sessions (intraclass correlation coefficients were .82 for maximal, and .58 for submaximal). As a result, the range of scores within which an individual's true score might be expected to lie was large (+/- 25 Nm for maximal, and +/- 37 Nm for submaximal). Although derived strength parameters like difference scores may be effective in distinguishing submaximal from maximal efforts completed by groups of subjects, the test-retest reliability of the present scores suggests that their use in judging an individual's performance may be limited.

Detecting submaximal efforts in grip strength testing with the coefficient of variation

The use of the coefficient of variation (CV) to determine level of effort in grip strength testing was examined empirically. Twenty-nine asymptomatic subjects participated in two conditions of testing: 100% effort and 50% effort. Order of conditions was counterbalanced and each subject was run in both conditions twice in the same order in order to assess the stability of the method. The number of trials (grasps) per condition was three for a total of 12 grasps for the study. The submaximal (50%) effort condition showed significantly more variability than the maximal effort condition in both sets of conditions (p<.01). Intra-class correlation coefficients were very low for both maximal effort and submaximal efforts (.036 and .025) indicating very low stability for the coefficient of variation. Classification rates were also found to have unacceptably large errors with 69% of the submaximal efforts being classified as maximal with the traditional 15% CV cutoff and 55% misclassification of submaximal efforts with an optimized 11% CV cutoff. It was concluded that the currently practiced method of using a low number of repetitions to calculate the CV may result in very unstable measures. Furthermore the "false negative" rate in using this method is unacceptably high for practical application. The implications of using the method and suggestions for improvement are discussed.