RESNA 26th International Annual Confence

Technology & Disability: Research, Design, Practice & Policy

June 19 to June 23, 2003
Atlanta, Georgia


Bhagwant S. Sindhu, Orit Shechtman
and Paul W. Davenport
University of Florida, Gainesville, FL


Clinicians frequently use strength testing to infer the outcome of rehabilitation in Work-related Musculoskeletal Disorders (WMSD). Only sincere effort makes the strength test valid. This study investigates the validity of a new method to detect sincerity of effort. This study hypothesizes that a subject relies on visual feedback rather than on proprioceptive feedback and by changing the difficulty level of performing the same visual task one can trick a subject exerting insincere/submaximal grip strength effort into exerting more effort than the subject intended. The instrumentation for this study includes a handgrip dynamometer, an oscilloscope, a signal processor unit, and a polygraph software system. The subject performs the grip task using visual feedback of reaching a target line on an oscilloscope by gripping a dynamometer. This target line is based on the subject's maximal grip effort. After establishing the target line, the investigator instructs the subjects to reach that line. The investigator then changes the gain without the subject's knowledge so that the subject has to exert twice as much effort to reach the line. Electromyographic (EMG) recording is also used to distinguish between maximal and submaximal efforts. The ratio of flexor and extensor muscle activity is hypothesized to be statistically different for maximal and submaximal efforts.


Clinicians diagnose WMSD when symptoms of pain, numbness, and/or tingling last more than a week or occur more than 20 times in a year in the absence of an acute traumatic onset or a systemic condition (1). Clinicians find it difficult to diagnose and treat WMSD due to poor localization, non-specificity and episodic nature of its symptoms. The annual cost of managing WMSD has escalated to approximately 20 billion dollars partially due to inaccurate diagnostic and assessment procedures. Accurate assessment of disability prior to and after rehabilitation allows clinicians to infer the treatment outcomes. In an attempt to improve WMSD rehabilitation outcomes, health care professionals have tried to identify any kind of symptom magnification by injured workers. A person cannot be effectively rehabilitated despite the most advanced technology, equipment or treatment methods when the person magnifies symptoms. Symptom magnification implies that the worker consciously or unconsciously exaggerates disability. Clinicians use exertion of insincere effort as an indicator of symptom magnification.

Clinicians commonly use grip strength scores to ascertain a worker's disability level, the amount of injury related financial compensation, and to predict return to work. Insincere effort in grip strength denotes that a person does not give a full and maximal effort when asked to perform a strength test. Insincere effort in grip strength testing may result in inaccurate rehabilitation outcomes. The three most commonly used clinically-relevant methods for grip strength assessment include the rapid exchange grip test, the five-rung test, and the coefficient of variation of three or more trials. These assessments do not detect sincerity of effort (2; 3). The EMG output of forearm muscles activated during maximal and submaximal grip exertions has been studied as a method for detecting sincerity of effort (4). EMG studies showed significantly different maximal and submaximal muscle activation patterns (5). The subjects, however, performed both maximal and submaximal efforts in the absence of any variability in the difficulty level of the task, making the comparison between the two levels of effort easy and obvious.

There is a need for a study that measures sincerity of effort in grip strength test by blinding the test administrator to the amount of effort exerted by the subjects and also blinding the subjects to amount of force necessary to perform a grip strength task. This measurement of grip effort maybe possible when using instrumentation that combines an oscilloscope, a hand dynamometer with an electronic readout on the oscilloscope and computer, signal processor unit and a polygraph software system (see Appendix A for pictorial representation of the various instrumentation components). We use an oscilloscope from Gould Instruments as it can transmit EMG output. The Grass Transducers filter the force output from the dynamometer (Biopac Instruments) and the EMG outputs. The Chart software from ADI Instruments digitizes these filtered outputs. The analysis of the data from this digital output may indicate a statistically significant difference between sincere and insincere grip strength trial.


The hypotheses for the study were:

  1. Subjects who exert insincere/submaximal effort will be tricked into exerting higher force during reduced gain trials.
  2. The ratio of flexor to extensor EMG will be statistically different for sincere/maximal grip strength trials from insincere/submaximal effort.


This study uses repeated measures design with 30 healthy subjects to analyze the difference between sincere/maximal and insincere/submaximal grip strength effort. The instrumentation for this study consists of a dynamometer (to measure grip strength), an oscilloscope (for subjects to observe grip output), EMG unit, signal processor unit and a computer with polygraph software. The subjects grip the dynamometer in a standardized position. We record the surface EMG of Flexor Digitorum Superficialis and Extensor Digitorum, and grip force data of each strength trial.

The subjects participate in 2 sessions in a random sequence of maximal or submaximal effort. Each session comprises of 11 grip strength trials. The first 3 trials of each session assist in establishing average maximal or submaximal grip strength target line on the oscilloscope. The test administrator sets the resistance/gain of the dynamometer at 1 unit for the first 3 trial sessions. The test administrator's assistant sets the target line to the highest level of effort applied by the subjects while gripping the dynamometer in the trials 1 to 3. Neither the subjects nor the test administrator view the grip outputs on the oscilloscope during the trials 1 to 3. In the trials 4 to 7, the test administrator instructs the subjects to reach the target line on the oscilloscope set in the first 3 trials. The test administrator leaves the resistance/gain at 1 unit for trials 4 to 7. The test administrator randomly increases the resistance/gain to 2 units in two of the last four trials (trials 8 to 11) making it twice as hard to reach the target line set at the beginning of the session. We will use paired t-tests to compare the EMG ratios and analysis of variance to examine the difference in force generated when the test administrator changes the resistance in maximal and submaximal sessions making it harder to reach the target line.


This study is a one year project with an anticipated end date of March 2003. This study specifically examines an empirical method to detect sincerity of effort in grip strength. This study will indicate that a force dynamometer, oscilloscope and EMG can help clinicians with accurate measurement of grip strength and identify insincere effort. The visual feedback from the oscilloscope forces the subject to focus on the target line rather than application of force during a grip strength trial. On exerting maximal effort, the subject applies consistent effort. When the test administrator increases the resistance in a maximal effort trial, the subject still exerts similar amount of effort even though he/she cannot reach the target line. When exerting submaximal effort, the subject does not apply consistent effort and when the test administrator increases the resistance, the subject tries to reach the target line thus exerting more than the submaximal effort he/she applies in the trials with only 1 unit of resistance/gain. This protocol when validated further needs to be tested in a clinical setting. The instrumentation also needs to be engineered to make it portable and inexpensive.

With the validation of this protocol, we will provide the foundation for collaborative and systematic investigation of the rehabilitation process used for WSMD. With a valid method to measure effort, we can identify the components of the rehabilitation process that do not enhance the client's recovery.


  1. Sanders, M. J. (1997). Management of cumulative trauma disorders. Boston: Butterworth-Heinemann.
  2. Robinson, M. E., Geisser, M. E., Hanson, C. S., & O'Connor, P. D. (1993). Detecting submaximal efforts in grip strength testing with the coefficient of variation. Journal of Occupational Rehabilitation, 3(1), 45-50.
  3. Shechtman, O., & Taylor, C. (2000). The use of the rapid exchange grip test in detecting sincerity of effort, part II: Validity of the test. Journal of Hand Therapy, 13(3), 203-210.
  4. Janda, D.H., Geiringer, S.R., Hankin, F.M., & Barry, D.T. (1987). Objective evaluation of grip strength. Journal of Occupational Medicine, 29(7), 569-571.
  5. Niebuhr, B.R. (1996). Detecting submaximal grip exertions of variable effort by electromyography. Electromyogr Clin Neurophysiol, 36(2), 113-120.


This study is funded by the University of Florida Opportunity Grant # 02050262. Special thanks to Camille L Swartz for her assistance in the implementation of this study.

Bhagwant S. Sindhu, MS, OTR
c/o Orit Shechtman, Ph.D., OTR/L
Department of Occupational Therapy - University of Florida
P.O. Box 100164, Gainesville, FL 32610
Voice (352) 846-1018, Fax (352) 846-1021



Figure 1: The Gould Instruments Oscilloscope
Figure 1: The Gould Instruments Oscilloscope

Figure 2: The Grass Transducers making the Signal Processor Unit
Figure 2: The Grass Transducers making the Signal Processor Unit


Figure 3: The Biopac Instruments Handgrip Dynamometer
Figure 3: The Biopac Instruments Handgrip Dynamometer
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