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Research

Click on this text to see a list of the published studies and reviews which indicate the most commonly-used hand strength assessments of validity of effort are highly inaccurate and should not be used.

The abstract below proves the X-RTS Hand Strength Assessment is demonstrably superior to all other tests for validity of effort in the testing of the hands.  Scroll down the page to download the four articles we have recently had accepted for publication.

Schapmire D, St. James JD, Townsend R, Stewart T, Delheimer S, Focht D, Simultaneous Bilateral Testing: Validation of a New Protocol to Detect Insincere Effort During  Grip and Pinch Strength Testing, Journal of Hand Therapy, Volume 15, Number 3, July-September 2002, pgs. 242-250. 

Abstract: The detection of feigned weakness in hand-grip strength assessment is difficult. We review several proposed methods and their weaknesses. A comparison of unilateral testing and simultaneous bilateral testing with the Jamar™ dynamometer and the Baseline™ pinch gauge is demonstrated as a solution. An experiment employed 100 asymptomatic subjects tested twice, once under instructions to give a full effort and once under instructions to feign weakness. Seven statistical criteria of noncompliance were chosen. Defining noncompliance as failing two or more of the seven criteria, 99% of the instructed-noncompliant subjects were correctly classified as noncompliant. No subjects were incorrectly classified as noncompliant during instructed compliant testing. Twelve subjects failed a single criterion. On retesting, all but one were correctly classified. One subject in the instructed-noncompliant group passed all criteria. Including retesting of the 12 "grey-zone" subjects, accuracy was 99.5%.

A follow-up study of a patient population has been recently accepted for publication.  The abstract appears below.  The study below rejects 30 years of “conventional wisdom” that "pain" will cause patients to fail validity criteria at a higher rate than persons without objective findings---at least for the criteria in the X-RTS Hand Strength Assessment.

Schapmire D, St James JD, Feeler L, Kleinkort J. Simultaneous Bilateral Hand Strength Testing in a Client Population, Part I:  Diagnostic, Observational and Subjective Complaint Correlates to Consistency of Effort.  Accepted for publication in Work, A Journal of Prevention, Assessment and Rehabilitation. 

Download the complete text of this manuscript by clicking on this line of text.

Abstract: This is a retrospective cohort study of 200 consecutive insurance claimants who were tested during a functional capacity evaluation (FCE).  Past study of normal subjects proposed simultaneous bilateral testing of the hands as a method of classifying effort as described by  Schapmire, St. James and Townsend et al. but no subsequent studies have assessed the applicability of the methodology to a patient population.   The purpose of this study was twofold:  to assess the observational correlates to test classification and to determine if “pain” is likely to account for a failure of the validity criteria.  Subjects filled out pain questionnaires, were observed for various behaviors and were administered the distraction-based hand strength assessment.  Patients failing two or more of the statistically-based validity criteria had higher scores on most pain questionnaires, presented with a higher frequency of various pain behaviors (p < .05 and <.0004, respectively), and had a lower rate of relevant surgeries (p < .001). There was no statistically significant difference in the number of failed validity criteria between this group of patients and for normal subjects feigning weakness in a controlled study (p > .05).  The protocol is appropriate in a patient population.

Part II of the study referenced above, combined with Part I, demonstrates what we have always suspected:  Behavior during a test is relatively constant.  Cooperative persons are cooperative throughout the test.  Uncooperative persons are uncooperative throughout the test.  There is a very high correlation between the results of the X-RTS Hand Strength Assessment and the results obtained during the lifting assessment.  The difference in these findings from previous studies is that the analysis of performance is based on the amount of variability between actual physical measurements—not on a “professional opinion” that can be easily challenged.

St James JD, Schapmire D, Feeler L, Kleinkort J. Simultaneous Bilateral Hand Strength  Testing in a Client Population, Part II: Relationship to a Distraction-Based Lifting Evaluation. Accepted for publication in Work, A Journal of Prevention, Assessment and Rehabilitation. 

Download the complete text of this manuscript by clicking on this line of text.

Abstract: This is a retrospective cohort study of 200 consecutive insurance claimants undergoing a functional capacity evaluation.  The purpose of this study was to determine whether a pattern of test behavior in one distraction-based test for the hands (involving simultaneous testing of both hands) predicts test behavior in a distraction-based lifting assessment when workloads are lifted on a second class lever arm.  The two testing protocols, one involving a hand strength assessment, the other involving an assessment of lifting capacities, were administered to assess the variability between repeated measures.  Clients failing two or more statistically-based hand strength validity criteria had significantly more variability between repeated measures in the lifting assessment, p = .001 and p =.014 for right and left unilateral lifts, respectively, and p <.001 for three different bilateral lifts.  The test outcome in one protocol (passing or failing the validity criteria.) is predictive of test behavior in the other.   

Periodically, isometric testing is resurrected, re-cycled and promoted for use as an objective and valid method of predicting dynamic lifting capacities.  In an evidence-based field, clinicians should be asking the question, "Where's the proof?"  In forty years of research involving isometric testing, the alleged linkage between isometric strength and dynamic function has been based on "statistically significant" correlations between subjects' static and dynamic capacities.  But a statistically significant relationship is not sufficient to make such predictions.  The abstract shown below is the largest study of its kind in terms of the number of subjects.  It is also important because the statistical calculation  (standard error of estimate) required to use static strengths to predict dynamic function was actually performed.  On the basis of these calculations, it is now known---definitively---that isometric measurements can not be used to predict dynamic function.  The implications of this study are potentially profound.  It is highly likely that hiring decisions made on the basis of isometric strengths will have a disparate impact on female job applicants because males have significantly higher static strengths.  Furthermore, it is possible that predictions related to dynamic function that are based on static measurements will result in persons being assigned to jobs that will be too physically demanding to perform safely.

Feeler L, St. James JD, Schapmire D.  Isometric Strength Assessment  I: Static Testing  Does Not Accurately Predict Dynamic Lifting Capacity.  Accepted for publication in Work, A Journal of Prevention, Assessment and Rehabilitation. 

Download the complete text of this manuscript by clicking on this line of text.

Abstract:  Published studies have generally found modest correlations between isometric and dynamic measures of strength.  Various systems for functional capacity evaluation and post-offer testing that are currently marketed rely on isometric testing to determine whether workers are able to perform specific job duties, including dynamic lifting.  Results of post-offer employment testing for 107,755 male and 23,078 female prospective workers are reviewed to determine if isometric strength measurements can be used to predict dynamic lifting capacity.  Subjects were tested for three standard static lifts and attained physical maxima for four dynamic lifts.  The data confirms modest correlations between isometric and dynamic measures.  However, the standard errors of estimate for all isometric-to-dynamic predictions make such predictions meaningless for the practical purpose for which they are most commonly used.  The Static Leg Lift, Static Arm Lift and Static Back (Torso) Lift are not appropriate for making predictions relative to dynamic lifting capacity.  Given the likely degree of error in such predictions,  and in light of potential safety concerns as reported by previous investigators, employers, clinicians and risk managers now have substantial objective evidence to call such testing into question.

Isometric testing has also been used to classify validity of effort for about 30 years.  Oddly enough, prior to the acceptance of the study below---in an evidence-based field---there had not been a single controlled study that demonstrated the accuracy of static testing in the classification of validity of effort.  

Townsend R, Schapmire D, St. James JD, Feeler L.  Isometric Strength Assessment II: Static Testing Does Not Accurately Classify Validity of Effort.  Accepted for publication in Work, A Journal of Prevention, Assessment and Rehabilitation. 

Download the complete text of this manuscript by clicking on this line of text.

Abstract: Isometric strength testing has been promoted as a type of physical test that can be used to assess sincerity of effort.  An extensive search of the literature finds no controlled studies in which two static lifts, the Static Arm Lift and Static Leg Lift are found to be either sensitive or specific in classifying validity of effort.  The purpose of this study was to determine if these two commonly-administered isometric tests are accurate indices of effort.  In this controlled study, 34 healthy subjects were tested once giving a maximum voluntary effort and once attempting to feign weakness of 50% of maximum.  During feigned weakness sessions, 20 of 34 subjects (58.5%), produced CVs of 15% or less during the Leg Lift.  At the 95% CI, the expected frequency of false negatives for feigned weakness is 42.3 to 75.3% for the Leg Lift.  At the 95% CI, the expected frequency of false negatives for feigned weakness is 51.9% to 83.3% for the Arm Lift.  Neither isometric lift is appropriate for classifying validity of effort.  Use of these isometric lifts should be discontinued for the assessment of effort. 

Stay tuned for more original research.  We will have quite a bit to say in the coming months about the so-called "visual estimation of effort" during a lifting task. 

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James D. St. James, Ph.D. and Darrell Schapmire, M.S.
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