Hand grip strength is a measure of. Reliability and validity of an electronic dynamometer for measuring grip strength

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1 Research Reliability and validity of an electronic dynamometer for measuring grip strength Deborah Allen, Fiona Barnett Aims: This article describes a study aiming to establish the concurrent validity and test-retest reliability of the Biometrics E-LINK EP9 electronic dynamometer. Methods: Grip strength testing was performed on 49 healthy participants. Three trials were completed for the right and left hands on the Biometrics and Jamar dynamometers, using a repeated measures design. Data was compared and used to establish concurrent validity of the Biometrics dynamometer. Fifteen participants repeated the testing a week later, for test-retest reliability of the Biometrics dynamometer. Findings: The Biometrics E-LINK EP9 evaluation system was found to have excellent validity (ICC ). However, a small but statistically significant difference between the right hand grip strength scores of the Biometrics (31.65 ± 8.89) and Jamar (30.44 ± 9.49) dynamometer was revealed (p 0.05). Test-retest reliability of the Biometrics system proved excellent, with ICC scores of for the left hand and for the right hand. Conclusions: The results indicate that the Biometrics E-LINK EP9 evaluation system is valid, reliable and comparable to the Jamar hydraulic dynamometer, when used for measuring grip strength with the second handle position. However, due to the statistically significant differences found for the right hand grip strength scores, therapists should exercise caution when interchanging instruments. Key words: n dynamometer n grip strength n test-retest Submitted 6 September, sent back for revisions 1 November; accepted for publication following double-blind peer review 19 November 2010 Deborah Allen is Honours Graduate, Occupational Therapy Discipline, James Cook University; and Fiona Barnett is Senior Lecturer, Occupational Therapy Discipline, James Cook University, Townsville, Australia Correspondence to: F Barnett fiona.barnett@ jcu.edu.au Hand grip strength is a measure of the force exerted by the hand during a maximum isometric contraction (Stechtman et al, 2003; Svens and Lee, 2005). The purpose of grip strength evaluation is to measure a person s grip strength relative to normative data, and to monitor a person s progress following hand injury or surgery (Stechtman et al, 2003; Svens and Lee, 2005). While there are a variety of instruments available for measuring grip strength, not all instruments have been proven to be reliable or valid (Stechtman et al, 2005). Fess (1968) stressed that the reliability and validity of a grip strength instrument is crucial to the quality of the results obtained. Therefore, establishing reliability and validity of an instrument is essential for clinical practice. Hand grip dynamometry is used for assessing upper limb impairment, work capacity following injury or disease and rehabilitation progression and/or potential following injury or surgery (Reuter et al, 2011). Reliability is the extent to which a measurement is consistent and free from error. Good test-retest reliability is the ability of an instrument to measure accurately and consistently over time (Stechtman et al, 2005). Intraclass correlation coefficient (ICC) is recommended for determining reliability, as it assesses the degree of association and agreement among instruments (Portney and Watkins, 2008; Vincent, 2005). Validity is the extent to which an instrument measures what it is intended to measure, and the most effective form of validity is criterion related validity (Mathiowetz, 2002; Stechtman et al, 2005). Criterion related validity is also defined as concurrent validity, and involves comparing an instrument to a gold standard in order to prove that the outcomes of one instrument can be used as a substitute measure for an established gold standard criterion test (Stechtman et al, 2005; Vincent, 2005). The Jamar hydraulic dynamometer was developed by Bechtol 258 International Journal of Therapy and Rehabilitation, May 2011, Vol 18, No 5

2 (1954) and is the tool most widely used by clinicians for hand grip measurement (Innes, 1999). Studies have since reported high validity and/or reliability of this instrument, and normative data referencing healthy populations have been developed for it (Stechtman et al, 2005; Svens and Lee, 2005). For these reasons, the Jamar is considered to be one such gold standard instrument, and many authors have used the Jamar as a criterion standard to validate other instruments, both hydraulic and electronic (Mathiowetz, 2002; Stechtman et al, 2003; Bohannon, 2005; Stechtman et al, 2005; Svens and Lee, 2005). Examples of hydraulic dynamometers with proven reliability and validity include the Baseline and Rolyan dynamometers, while examples of electronic dynamometers include the BTE-Primus and the DynEx dynamometers (Mathiowetz et al, 2000; Mathiowetz, 2002; Stechtman et al, 2003; Stechtman et al, 2005). E l e c t r o n i c o r c o m p u t e r c o n n e c t e d dynamometers offer advantages over hydraulic dynamometers including identifying fatigue index during a prolonged isometric contraction, increased sensitivity to applied force, digital readouts which increase interrate reliability and a decrease in manual reading errors, and automated calculations (Stechtman et al, 2005; Svens and Lee, 2005). One such electronic dynamometer that has recently become available is the Biometrics E-LINK EP9 evaluation system (Biometrics Ltd, Gwent, UK, 2006). The website of the Biometrics E-LINK EP9 dynamometer describes it as a computerised tool for evaluating grip strength in 0.1 increments (kg or lbs), and can perform tests that could not be done with manual devices (Biometrics Ltd, 2010.). The instrument is connected to the E-LINK software and measures grip strength with three different tests available: n Standard peak force grip test n Sustained grip test n Rapid exchange test. While there are no current data available on the reliability and validity of the Biometrics electronic dynamometer, four studies have used the criterion standard Jamar hydraulic dynamometer to evaluate the reliability and validity of other electronic dynamometers, including the GripTrack, BTE-Primus, MicroFET 4 and the DynEx dynamometers (Mathiowetz, 2002; Stechtman et al, 2003; Stechtman et al, 2005; Svens and Lee, 2005). Three of the four studies reported very good to excellent concurrent validity between the Jamar dynamometer and their respective electronic dynamometers (ICC= ) when using the second handle position (Stechtman, 2003; Bohannon, 2005; Stechtman et al, 2005). In contrast, one study reported reasonable to good concurrent validity (ICC<0.900) (Svens and Lee, 2005). Therefore, the purpose of this study was to establish the concurrent validity and test-retest reliability of the Biometrics electronic dynamometer, and compare it with the criterion standard hydraulic Jamar dynamometer for measurement of grip strength among healthy participants. This study aims to prove the hypothesis that the Biometrics E-LINK EP9 evaluation system is reliable, valid and comparable to the Jamar hydraulic dynamometer, when used for measuring grip strength on the second handle position. Methods Participants The participants were a convenient sample. Forty nine university students (seven males and 42 females) volunteered for this project. Participants were aged between 18 and 25 years with no known history of impaired cognitive functioning, physical disability, or current upper extremity injury. On meeting the Figure 1. Biometrics E-LINK EP9 Hand grip dynamometer. International Journal of Therapy and Rehabilitation, May 2011, Vol 18, No 5 259

3 Research above requirements for inclusion, participants completed the informed consent approved by a University Human Research Ethics Committee. Eighty-six percent of participants were right handed. Instruments One Jamar hydraulic dynamometer and one Biometrics E-Link grip strength attachment (G200) (Figure 1) were used to obtain static grip strength measurements on the second handle position of each dynamometer. Maximal grip strength was recorded in kilograms of force as the mathematical average of three successive trials. The Jamar dynamometer was calibrated using known weights to ensure accuracy prior to data collection. The Biometrics E-Link system was calibrated by the manufacturer prior to the study. Prior to the trials, familiarisation occurred via a demonstration by the test administrator and a practice trial by the participants. Procedure Participants grip strengths were evaluated using the Biometrics E-LINK EP9 system and Jamar hydraulic dynamometer to measure concurrent validity. Each grip strength test consisted of three maximal repeated contractions (trials) for each hand on the second handle position of the dynamometer. The testing was performed in a non-alternating manner in line with previous studies comparing electronic dynamometers with the Jamar (Bohannon, 2005; Svens and Lee, 2005; Stechtman et al, 2005): three grip strength trials were obtained for the right hand using the Jamar dynamometer then three trials were obtained for left hand using the Jamar. The process was then repeated using the Biometrics E-LINK EP9 evaluation system. The duration of each contraction was three seconds, with a 15 second break between trials, and a five minute break between instruments. Mathiowetz (1990) found that 15 second breaks between trials and five minute break between instruments is sufficient to reduce the impact of fatigue. Trial duration and rest periods were timed with a stopwatch. Fifteen of the forty-nine participants were re-tested a week later using the Biometrics evaluation system, using the above testing procedure to examine test-retest reliability. Specific positioning protocols were used throughout testing. Participants were positioned in the appropriate seated position as recommended by the American Society of Hand Therapists (ASHT): shoulders adducted and neutrally rotated, elbow flexed to 90º, forearm in neutral and wrist between 0 30º of extension and 0 15º of ulna deviation and feet flat on the floor (Bohannon and Schaubert, 2005). The participants were instructed to maintain this position throughout testing. To ensure consistency, participants received no visual or auditory feedback during testing, and were coached using the same standardised verbal directions. The directions given were as follows: First we will test your left hand. You will be required to grip the dynamometer as hard as you can, and then relax. I ll count for you and tell you when to relax. Go. One, two, three, relax. Ok, that was good. Again, grip as hard as you can, One, two, three, release. Good. The same standardised and reserved instructions and feedback were given for each trial, hand and instrument. Data analysis For the participant data, the average of the three trials was calculated and used as the grip strength score for each test. All grip strength measurements were expressed in kilograms of force. Concurrent validity was calculated to indicate consistency between the Biometrics E-Link EP9 Evaluation System dynamometer and the Jamar dynamometer. Test-retest reliability was calculated to indicate consistency of force measurements of the Biometrics evaluation system. Intraclass correlations (ICC) were performed to determine concurrent validity and test-retest reliability. ICC reliability has previously been determined to be an appropriate indicator of test retest reliability (Vincent, 2005). In addition, a repeated measures analysis of variance (ANOVA) with one withinparticipants factor of instrument (Biometrics versus Jamar) was conducted to determine whether differences in strength scores existed between instruments. Differences were considered significant at the 0.05 level of significance. Findings Prior to statistical analysis, data were examined to ensure that the assumption of normality were met. Variables were examined for kurtosis and skewness and the data were determined to be normally distributed. Normally distributed variables will have kurtosis values not exceeding 3, and skewness values not exceeding 2 (Vincent, 2005). Kurtosis values for the current study ranged from International Journal of Therapy and Rehabilitation, May 2011, Vol 18, No 5

4 to and skewness values ranged from to Data were also screened for outliers by examining box plots. Participant 4 was determined to be an outlier, and the data were excluded from further analysis. Descriptive statistics of grip strength scores for the Biometrics and Jamar dynamometers are provided in Table 1. The Biometrics E-LINK EP9 evaluation system was found to have excellent validity (r = 0.983; 0.986). The repeated measures ANOVA revealed no significant differences between the left hand grip strength scores, however a small but significant difference between the right hand grip strength scores of the Biometrics and Jamar dynamometer was found ( F = 14.81; p = 0.000) (Table 2). Test-retest reliability of the Biometrics system proved excellent for the left hand (r = 0.986) and for the right hand (r = 0.996). This suggests that the grip strength scores obtained with the Biometrics system were stable over the two testing periods. Discussion The advantages of using a computerised dynamometer include increased sensitivity to applied force, digital readouts which increase inter-rate reliability, a decrease in manual reading errors and the ability to evaluate grip strength to the closest 0.1 increments (kg or lbs) compared to the closest 5lb increments on the Jamar hydraulic dynamometer. However, the concurrent validity and reliability of the Biometrics E-LINK EP9 Evaluation System for measuring grip strength have not been reported. This study compared the electronic Biometrics dynamometer and the hydraulic Jamar dynamometer to provide the validity and reliability values of the Biometrics E-LINK EP9 Evaluation System based on data derived from healthy human participants. Validity and Reliability Concurrent validity Correlation coefficients greater than are considered reasonable for validity, however to fulfil the requirements of comparability of the instruments, the ICC value should exceed (Svens and Lee, 2005). The concurrent validity between the Biometrics and Jamar dynamometers was found to be excellent for both the right (0.986) and left hands (0.983), and indicates that both the Jamar and Biometrics dynamometers measure the same construct of grip strength. Results also Table 1. Mean ± SD of grip strength scores (kg) of the Biometrics and Jamar dynamometers n = 48 Biometrics Jamar Right hand ± ± 9.49* Left hand ± ± 9.62 *p <0.05 Table 2. ANOVA results for Biometrics and Jamar dynamometers Wilks Lambda Df F Sig of F Left Hand / Right Hand / * * Significant difference indicate that the Biometrics is a valid tool for measuring grip strength. These findings are similar to previous studies (Stechtman et al, 2003; Bohannon, 2005; Stechtman et al, 2005; Svens and Lee, 2005) that have used the gold standard Jamar dynamometer as a criterion standard, correlating it to various grip strength electronic tools (DynEx, GripTrack, BTE-Primus and MicroFET 4) to establish concurrent validity and inter-instrument reliability. These studies revealed good to excellent concurrent validity and inter-instrument reliability scores, with values ranging from to (Stechtman et al, 2003; Bohannon, 2005; Stechtman et al, 2005; Svens and Lee, 2005). Despite the excellent concurrent validity values, significant differences in the right grip strength scores between the Jamar and Biometrics dynamometers were revealed. Mean grip strength scores of the right hand measured with the Biometrics dynamometer were slightly but significantly higher than those measured with the Jamar. This indicates that the Biometrics is comparable to the Jamar dynamometer when measuring the left hand, however it is not as comparable when measuring the right. One previous study that compared an electronic dynamometer to a hydraulic dynamometer revealed similar results, with the MicroFET 4 having significantly higher average means for the left hand than the Jamar (Bohannon, 2005). Although the high correlation coefficient indicates association between two or more scores (in this case the grip strength scores obtained on the two instruments), comparison testing (ANOVA) revealed significant statistical differences between scores International Journal of Therapy and Rehabilitation, May 2011, Vol 18, No 5 261

5 Research obtained on the two instruments. Therefore, if one instrument demonstrates consistently higher scores than the other, it is possible to find significant differences between the scores obtained on the two instruments, and yet obtain a high concurrent validity correlation coefficient between the two instruments (Stechtman et al, 2005). Despite the significant differences found in the current study between mean grip strength scores for the right hand, the high concurrent validity suggests that the Biometrics is equivalent to the Jamar in obtaining grip strength scores. Only instruments that have low values and significantly different statistical results for concurrent validity are determined to not measure grip strength with reasonable comparability to the Jamar dynamometer (Stechtman et al, 2005). The findings of this study indicate that, when used under the same conditions as outlined in the methodology, clinicians can use the Biometrics on the second handle position and know that it is reliable, valid and comparable to the second hand position of the Jamar dynamometer. Test re-test reliability According to Fess (1968), the effectiveness of an instrument cannot be determined without reliability and validity values. Good reliability is indicated by correlation coefficients of greater than 0.750, however with clinical measurement reliability values should exceed (Stechtman et al, 2003). The findings of the present study revealed excellent test-retest reliability values for the Biometrics dynamometer. This indicates that the Biometrics is consistent in measuring grip strength scores, and suggests the grip strength scores were stable over the two testing sessions for the Biometrics dynamometer. Previous studies (Stechtman et al, 2003; Stechtman et al, 2005) of test-retest reliability of electronic dynamometers including the DynEx and BTE-Primus, have shown high test-retest reliability values ranging from to Handle position Throughout this study, data was obtained using the Jamar and Biometrics dynamometers, with both instruments set to the second handle position. As the Jamar and Biometrics have different handle shapes, and the Jamar handle is positioned at a slightly further distance from the base of the dynamometer than the Biometrics when in the second handle position, depending on hand size, many participants may not have been able to obtain optimum hand and finger position to produce maximal grip strength. A study of 288 participants by Firrell and Crain (1995) found that 89% of participants had maximal grip strength on the second handle position, however since no clear significant correlation between hand size and maximal handle setting was evident, it was recommended that grip strength of all participants should be consistently measured at the second handle setting irrespective of age, weight or hand dimensions. Instrument design While there are several instruments available for measuring grip strength, the Jamar hydraulic dynamometer is used most often and is regarded as the gold standard of grip strength measuring devices. For this reason it is most often used as a criterion standard to establish the reliability and validity of newer grip strength measuring instruments (Stechtman et al, 2005). However, differences in the design of the instruments being compared, including handle shape, weight and data display, may contribute to significantly different results between the two instruments, as seen with the current study (Bohannon, 2005; Svens and Lee, 2005). The handle of the load cell of the Biometrics is a slightly different shape and, when in the second handle position, results in a grip expanse that is several millimetres larger than the hydraulic Jamar in the same handle position. This would increase the force exerted by the subject onto the Biometrics grip strength attachment. Although the hydraulic Jamar dynamometer measures grip strength accurately (±3%), it incorporates a dial display which is differentiated by 5lb intervals (Stechtman et al, 2003; Stechtman et al, 2005). As a result, this display feature has the potential to contribute to measurement error through manual reading error, as the tester had to estimate the grip strength score when the needle stopped outside the marked numbers. The Biometrics electronic dynamometer, however, is computer connected, and records grip strength measurements to the nearest tenth of a kilogram, on a digital display. This decreases the potential of measurement error and increases inter-rater reliability, as results obtained by different testers are automatically recorded by the software. Electronic dynamometers also have 262 International Journal of Therapy and Rehabilitation, May 2011, Vol 18, No 5

6 increased sensitivity to applied force, which therefore enables electronic dynamometers, such as the Biometrics to record low grip strength scores that may not have registered on the Jamar. Testing procedure A wide range of testing positions and procedures have been developed for grip strength testing, however it is generally agreed that standardised testing position and procedure are necessary when establishing the reliability and validity of new instruments. As with the current study, the standard seated position recommended by the ASHT for measuring grip strength is generally used by authors when comparing electronic dynamometers to the hydraulic Jamar dynamometer in order to establish concurrent validity and interinstrument reliability (Stechtman et al, 2003; Bohannon, 2005; Stechtman et al, 2005; Svens and Lee, 2005). Testing procedures used when establishing the reliability and validity of a new instrument vary widely. Basic testing procedure involved obtaining grip strength measurements from three trials of each hand with both instruments, in this case, the Jamar and Biometrics dynamometers. This repeat testing often causes a noticeable decrease of grip strength over time, and this is an indication that fatigue is present (Svens and Lee, 2005). Fatigue is a compounding variable that should be avoided to in order to ensure consistency of results. To decrease the risk of fatigue impacting on the study results, rest periods between trials and instruments were used. Rest period durations used in this study were 15 seconds between trials, and a five minute interval between instruments. Previous studies (Stechtman et al, 2003; Bohannon, 2005; Stechtman et al, 2005; Svens and Lee, 2005) have used rest periods of 15, 30, and 60 seconds between trials, and no significant differences between the rest period durations were found. A study conducted by Mathiowetz (1990) found that rest periods of 15 seconds between trials and five minutes between instruments were adequate to reduce the effects of fatigue when using three second trials. Stetchman et al (2003), however, found that rest periods as outlined by Mathiowetz (1990) were insufficient to reduce the effects of fatigue when using trials longer than three seconds. Therefore, fatigue was determined not to be a contributing factor to the significantly different results revealed in this study, as three second trials and appropriate rest breaks, as outlined by Mathiowetz (1990), were used. Limitations The main limitation of this study was the small sample size (n = 49) which may have reduced the generalisability of this study. Although the sample was sufficient to provide adequate statistical power for the intraclass correlation coefficients, it may have prevented the realisations of significant differences in some comparisons. The small sample size of unequal demographics (males = 7, females = 42; right hand dominant = 86%) meant that the study was not representative of the target population, and the application of more detailed analysis and the influence of confounders, e.g., effects of hand dominance and gender, could not be explored adequately. The small age range present in the convenience sample also meant that this study was unable to establish age norms for the Biometrics dynamometer. Another limiting factor may have been related to the handle position of the instrument during testing. The handles of the dynamometers, when in the second handle position, are slightly different in regards to the distance from the bases of the instruments. This difference in the distance between the instruments, in combination with differences in hand size, may have resulted in participants not being able to obtain optimal hand and finger position in order to produce maximal grip strength. The dial display of the Jamar dynamometer was another limitation of the instrument, as the tester was required to estimate results when the needle stopped outside one of the 5kg interval readings. This may have contributed to measurement error and in turn impacted on the results of the study. Practical implications The successful undertaking of many activities of daily living requires a certain degree of hand grip strength. As hand grip strength is affected by injury and disease it is important that accurate grip strength measurement is employed for rehabilitation progression in clinical practice (Reuter et al, 2011). It is therefore vital that validity and reliability data be established for electronic hand grip dynamometer systems as they become available. This study has established that the Biometrics International Journal of Therapy and Rehabilitation, May 2011, Vol 18, No 5 263

7 Research E-LINK EP9 evaluation system is a valid and reliable measurement tool to use by rehabilitation professionals. Recommendations Future studies into the reliability and validity of the Biometrics E-LINK EP9 evaluation system should be conducted using a larger sample that is representative of the target population in age, gender and hand dominance. Results from such studies could then be generalised to the larger population, and normative data for the Biometrics dynamometer could be established and programmed into the software. While this study determined the second handle position of the Biometrics E-LINK EP9 evaluation system to be reliable, valid and comparable to the second handle position of the Jamar dynamometer, future studies should be conducted to determine the reliability and validity of the other four handle positions of the Biometrics in relation to the Jamar dynamometer. The accuracy of the Jamar and the Biometrics dynamometers were established using known weights prior to data collection, however the instruments were not calibrated throughout the study as they were only used for two testing sessions. It is recommended that when using hand dynamometers frequently in clinical practice that they are calibrated at least every three months (Svens and Lee, 2005). Even though the accuracy of an electronic dynamometer may have been established using known weights and the concurrent validity with a Jamar dynamometer has been established, the ability to interchange grip strength dynamometers should never be assumed. This is due to the differences in calibration and age of the individual instruments, and for these reasons it is recommended that the same instrument should be used throughout a person s rehabilitation period, until inter-instrument reliability is established (Stechtman et al, 2005; Svens and Lee, 2005). Key points n Determining the reliability and validity of an instrument is essential before it is applied to clinical practice. n The Biometrics E-LINK EP9 evaluation system is a valid and reliable tool for measuring grip strength. n The Biometrics E-LINK EP9 evaluation system allows for ease and accuracy when assessing or monitoring patients. Conclusion Despite the limitations of this study, the results suggest that the Biometrics E-LINK EP9 evaluation system is valid, reliable and comparable to the Jamar hydraulic dynamometer when used for measuring grip strength on the second handle position. However, due to significant differences found between the right hand grip strength scores between the two instruments, therapists should exercise caution when interchanging instruments and it is recommended that the same dynamometer be used to measure grip strength of a patient throughout their treatment programme. IJTR Conflict of interest: none Bechtol C (1954) Grip test: the use of a dynamometer with adjustable handle spacings. J Bone Joint Surg Am 36-A(4): Biometrics Ltd (2010) Biometrics Ltd H500 Hand Kit. Online. (accessed 15th April 2011) Bohannon R (2005) Parallel comparison of grip strength measures obtained with a MicroFET 4 and a Jamar dynamometer. Percept Mot Skills 100(3 Pt 1): Bohannon R, Schaubert K (2005) Test-retest reliability of grip-strength measures obtained over a 12-week interval from community-dwelling elders. J Hand Ther 18(4): Fess E (1968) The need for reliability and validity in hand assessment instruments. J Hand Surg Am 11(5): Firrell J, Crain G (1995) Which setting of the dynamometer provides maximal grip strength? J Hand Surg 21(3): Innes E (1999) Handgrip strength testing: A review of the literature. Aust Occup Ther J 46: Mathiowetz V (1990) Effects of three trials on grip and pinch strength measurements. J Hand Ther 3: Mathiowetz V, Vizenor L, Melander D (2000) Comparison of Baseline instruments to the Jamar dynamometer and the B&L Engineering Pinch Gauge. Occupational Therapy Journal of Research 20(3): Mathiowetz V (2002) Comparison of Rolyan and Jamar dynamometers for measuring grip strength. Occup Ther Int 9(3): Portney L, Watkins M (2008) Foundations of Clinical Research: Application to Practice 3rd edn. Pearson/ Prentice Hall, Upper Saddle River Reuter SE, Massy-Westropp N, Evans AM (2011) Reliability and validity of indices of handgrip strength and endurance. Aust Occup Ther J 58(2): 82 7 Stechtman O, Gestewitz L, Kimble C (2005) Reliability and validity of the DynEx dynamometer. J Hand Ther 18(3): Stechtman O, Davenport R, Malcolm M, Nabavi D (2003) Reliability and validity of the BTE-Primus grip tool. J Hand Ther 16(1): Svens B, Lee H (2005) Intra- and inter-instrument reliability of grip-strength measurements: GripTrack and Jamar dynamometers. Br J Hand Ther 10(2): Vincent W (2005) Statistics in Kinesiology. Human Kinetics, Champaign: International Journal of Therapy and Rehabilitation, May 2011, Vol 18, No 5

8 COMMENTARies Therapists require accurate data for hand grip strength to assess impairment and evaluate rehabilitation following injury, surgery, or disease. Recent advances in technology have produced several promising tools that may make this assessment more reliable and accurate. For example, electronic and computer-linked dynamometers have several advantages over conventional hydraulic dynamometers, including increased sensitivity and automated data entry and calculation. This article The article evaluates the validity and reliability of an electronic dynamometer, the Biometrics E-LINK EP9, and compares it directly with an industry standard, the Jamar hydraulic. The results indicate that the Biometrics system is valid, reliable, and comparable to the Jamar system under the experimental conditions. The difference in sensitivity (increments of 0.1 kg or lb for the Biometrics versus 5 lb for the Jamar) alone makes the electronic The results indicate that the Biometrics system is valid, reliable, and comparable to the Jamar system under the experimental conditions. dynamometer attractive to therapists evaluating injured patients. I liked this article. The methods and results are presented clearly, the conclusions are straightforward, and the findings are put into context of previous research in the field. It remains to be seen if the small, albeit statistically significant, difference in right hand strength measured by the two instruments is of practical significance in the clinical setting. In any case, therapists may want to use the same instrument when evaluating an individual patient. I would have liked to seen a comparison of price of the instruments, but this is a minor point. I suggest that future studies include a wider range of age and demographics (with respect to gender and hand dominance) of the test subjects in order to generate a more comprehensive set of norms. Conclusions I am concerned, however, with the design of the handles of both instruments. This is not a shortcoming of the article, but there is a lack of available instrumentation for measuring grip or pinch strength of people with reduced web spaces. The handles of the dynamometers are too thick to measure grip or pinch strength of a patient who has lost multiple fingers and/or has reduced prehension. I would like to see development of electronic- or computer-linked dynamometers that can accurately and reliably measure grip or pinch strength for these extreme cases. Martin A. Stapanian, Ph.D. Research Ecologist Huron, Ohio, USA mastapanian@bex.net It is very important to use equipment that is validated, and reliability evaluated. The background for all treatment should be evidence based. For an occupational therapist working in a clinical practice it is very important to use equipment that is validated, and reliability evaluated. Most therapists working with patients following hand injury or surgery evaluate the progress of a treatment using the Jamar dynamometer for the grip strength test. The reason is, of course, because the Jamar dynamometer is tested for reliability and validity. The use of Jamar dynamometer is well described and easy to follow. This article evaluates one of the newer, computerised, dynamometer systems that have appeared on the arena for measuring grip strength. Examples of these systems are the GripTrack, BTE-Primus, MicroFET 4 and the DynEx dynamometers. Earlier articles have found that by using the Jamar Dynamometer as a gold standard, those dynamometers can be evaluated for reliability and validity, and three out of the four studies described very good to excellent concurrent validity between the Jamar dynamometer and their respective electronic dynamometers. The Biometrics electronic dynamometer has not been evaluated before, therefore this study compares the criterion standard hydraulic Jamar dynamometer with the Biometrics electronic dynamometer for validity and test-retest reliability by measuring grip strength on healthy participants. The study The methodology of the study is clearly described, and uses the manual from the Jamar dynamometer; the same procedures for testing the hand grip strengths are used for the two instruments according to the recommendation by the American Society of Hand Therapists (ASHT). I found it interesting that I could not tell from this article if the same test administrator was in charge of all the measurements. The authors have shown that the Biometrics E-LINK EP9 has excellent validity, with a small but notable difference between the right hand strength scores. The test-retest reliability showed excellent for the both hands. However, the small sample size (n = 49) and the unequal demographics made the result less powerful, and also made it impossible to establish age norms for the Biometrics dynamometer. Conclusions This article shows the importance of using instruments that are evaluated and proven valid and reliable for therapists working in this area. It is also important to use new computerised systems because they decrease the likelihood of recording error, since the measurements are automatically recorded by the software. Hélène Fitinghoff Occupational Therapist, University Lecturer, Karolinska Institutet, Stockholm Helene.fitinghoff@ki.se International Journal of Therapy and Rehabilitation, May 2011, Vol 18, No 5 265