Comparison of the BTE tech EVJ handgrip to the Jamar hand dynamometer for measuring grip strength

Abstract

INTRODUCTION:

This study compared the inter-instrument reliability of the Jamar Hand Dynamometer (Jamar) to the BTE EVJ Handgrip tool (EVJ). The EVJ is a new digital handgrip instrument designed by BTE Technologies Inc. (BTE Tech) utilizing Bluetooth technology to automatically upload data to a computer or electronic health record.

METHOD:

This repeated measure study engaged 338 participants ( $N=$ 199 females, $N=$ 139 males) ages 20 to 50. All participants were tested on both devices following the protocol established by the American Society of Hand Therapists (ASHT).

RESULTS:

Comparative statistics included ICC values (0.81–0.84), Pearson R (correlation coefficient) (0.68–0.77), and Bland Altman plots (93–95% of data within 2 SD), indicating good inter-instrument agreement.

CONCLUSIONS:

The EVJ Handgrip, developed by BTE Technologies, demonstrated good inter-instrument reliability with the Jamar Hand Dynamometer and may be reliable to use when referencing the published normative values in the clinical environment.

Keywords

Dynamometer industrial rehabilitation hand function grip strength functional capacity evaluation

1. Introduction

Grip strength is defined as a measurement of the maximum isometric contraction of the intrinsic and extrinsic hand and forearm muscles [1, 2, 3]. Accurate grip strength measurements may be a strong indicator of the extent of an injury, post-operative health, rehabilitation progress, ability to return to work, survival rate, disease, disability, and overall well-being [1, 4, 5, 6]. Normative standards also allow for additional interpretations of grip strength measurements by allowing comparison to others within the same age group [3]. In a clinical setting, these measurements facilitate the clinical reasoning process, ultimately allowing clinical practitioners to further understand their clients’ abilities and determine appropriate intervention strategies [7]. Additionally, when re-evaluating clients, new measurements may be taken and compared to baseline data and normative standards, to assess intervention progress, determine the need for plan of care modifications, and predict discharge disposition.

Grip strength is effectively measured utilizing a handgrip dynamometer, such as the Jamar Hand Dynamometer (Jamar) [1, 2, 3]. The American Society for Hand Therapists (ASHT) and American Society for Surgery of the Hand (ASSH) recommend the Jamar as the gold standard due to its consistent demonstration of high validity, test-retest reliability, and inter-rater reliability [8, 9, 10, 11, 12, 13, 14]. Several dynamometer variants are available for clinical use; however not all have been tested to establish reliability as compared to the Jamar [15]. Devices that do not undergo rigorous testing may provide unreliable results that may compromise the clinical outcomes of clinical interventions [1]. In addition, practitioners utilizing dynamometers that have not been tested may not assume that the results are comparable to the normative values established using the Jamar [16].

Numerous dynamometers have been compared to the Jamar to establish reliability of these devices. Amaral et al. [1] compared the accuracy and reliability of the Jamar to dynamometers with varying handle shapes and sizes. Results indicated that the tested dynamometers were not interchangeable with the Jamar and that handle shape and positioning affect grip strength scores. Allen and Barnett [15] demonstrated that a digital dynamometer, the Biometrics E-LINK EP9 is valid, reliable, and comparable to the Jamar. The study also emphasized the significance of electronic dynamometers for clinical use, as they provide precise digital measurements, ultimately reducing the risk of reading errors.

The purpose of this study was to compare the inter-instrument reliability of the EVJ Handgrip (EVJ), a new digital dynamometer developed by BTE Technologies, Inc. (BTE Tech), to the Jamar Hand Dynamometer (Jamar). The handle design and overall operation of the EVJ is similar to the Jamar, therefore, the developers expected the device to have good intraclass correlation when compared to the Jamar. Bland-Altman Plots [17] were also calculated to assist in determining the confidence. High levels of confidence with these measures may indicate that the EVJ is reliable as compared to the Jamar and that the handgrip normative standards may be applied when evaluating their clients [3]. In addition to determination of reliability, use of Bland-Altman Plots may also allow practitioners to determine if the devices can be used interchangeably and demonstrate agreeable results [12] .

2. Methods

Approval for the study was received from the Florida Gulf Coast University Institutional Review Board and was assigned protocol #2018-28.

2.1 Design

This reliability study used a repeated measures design as well as accumulation of qualitative data regarding participant opinions on the comfort of the EVJ versus the Jamar. Following ASHT protocol, left and right grip strength measurements were taken with each device [7]. To control for fatigue, participants were randomly assigned to initiate the study with either the EVJ or the Jamar then provided a 5-minute break before switching devices. Each participant returned for two additional trials. The design of this study was consistent with previous comparison studies of the Jamar to other grip strength devices [16, 18].

2.2 Participants

A convenience adult population of 199 females (mean age 25) and 139 males (mean age 26) was recruited Southwest Florida. Inclusion criteria required that participants be healthy, not pregnant, between 20–50 years old, and with no known history of upper extremity pathology that may affect hand strength. Ninety-one percent of females ( $N=$ 181) and eighty-four percent of males ( $N=$ 117) identified as being right hand dominant. All potential participants were required to read and sign an electronic informed consent form, then provided a questionnaire to determine eligibility and assigned an anonymous identifier if deemed eligible for the study.

Figure 1.

EVJ handgrip.

Figure 2.

BTE Tech EVJ Handgrip in use.

2.3 Instruments

The EVJ Handgrip is a digital dynamometer that was recently developed by BTE Technologies, Inc (Figs 1 and 2). The EVJ is adjustable with five frets to accommodate varying hand sizes. Measurements are obtained through Wheatstone bridge transducers that are embedded in the handle of each device and allow for a minor deflection of the handle while it is being squeezed. A microprocessor then converts the electrical signal into a force reading which is displayed on a computer using provided software (https://www.btetechnologies.com/rehabilitation/evj/). The EVJ automatically calculates the maximum grip strength per trial, average grip strength after at least two trials, and the coefficient of variation after three trials. All grip strength measurements are reported to the nearest tenth of a kilogram or pound with a ceiling of 90 kilograms (200 pounds). The EVJ Handgrip includes a calibration kit preventing the need for external calibration. In addition, the EVJ has an optional additional handle, mounted opposite the participant, to allow the evaluator to keep a light hold of the device if there are concerns of dropping the device. This feature can be removed if not desired.

The Jamar Hand Dynamometer is considered the gold standard in measuring static grip strength [10, 11]. As with the EVJ, the Jamar has a 90-kilogram (200 pound) limit and five frets [18]. The Jamar provides an analog display built into the handle in intervals of two kilograms or five pounds. It is recommended that the Jamar be recalibrated either by the manufacturer or an independent engineering lab as needed [19].

Table 1
Performance comparison of the BTE EVJ Handgrip to the Jamar Hand Dynamometer for females ( $n=$ 199) and males ( $n=$ 139). All measurements recorded in kilograms

Gender	Hand	EVJ	Jamar	Cohen’s d	ICC	$t$ (197) female $t$ (137) male	$p$ -value
Female	R	M 28.6	M 30.0	0.10	0.84	0.74 NS	$p<$ 0.000
		SD 13.89	SD 14.18
Female	L	M 26.3	M 28.6	0.17	0.84	0.77 NS	$p<$ 0.000
		SD 13.34	SD 13.36
Male	R	M 46.3	M 46.7	0.02	0.81	0.68 NS	$p<$ 0.000
		SD 24.91	SD 23.12
Male	L	M 42.7	M 45.0	0.16	0.84	0.74 NS	$p=$ 0.092
		SD 13.89	SD 14.18

NS $=$ no significant differences between the means of the instruments.

2.4 Procedure

Five Jamar dynamometers and five EVJ Handgrips were utilized for data collection. Each EVJ device was numbered from one to five and paired with a Jamar with the corresponding number. Only corresponding devices were utilized together throughout the study. Prior to the beginning of the study, the Jamar devices were calibrated by an independent engineering lab while the EVJ Handgrips were bench checked by BTE Tech engineers. To maximize reliability and consistency, each device handle was set to the second fret throughout the study [20]. To reduce the risk of bias and effects of fatigue, the order in which instruments were administered to the participants was determined using a random number generator.

Assessment of grip strength was conducted according to ASHT protocol, which includes: Participants seated with feet flat on the floor, shoulder adducted, forearm in neutral, elbow flexed to 90 ${}^{\circ}$ , wrist positioned at 0 ${}^{\circ}$ –30 ${}^{\circ}$ of extension, and wrist in 0 ${}^{\circ}$ –15 ${}^{\circ}$ of ulnar deviation [15]. Testing began using each participant’s dominant hand and measurements were taken three times bilaterally with each device. Participants were instructed to squeeze the dynamometer handle as hard as they could for three seconds. A five-minute break was provided before switching dynamometers to reduce effects of fatigue. Peak scores for each trial were averaged and recorded in pounds of force. Results were also converted into kilograms for this publication. To ensure quality of data collection, frequent observations of testing protocols were performed by a neutral observer.

After the completion of the trial, participants were asked to complete a post-participation survey. Participants were asked to identify which device was preferable and describe aspects of each device they found comfortable or uncomfortable. Results were analyzed to determine whether a correlation existed between device preference and grip strength measurements.

2.5 Data analysis

For each device, the average of the three trials and standard deviation (SD) were calculated using Microsoft Excel which was utilized to calculate the coefficient of variation (CV). IBM SPSS version 25.0 was utilized to complete Pearson’s correlation coefficients for concurrent validity ( $p<$ 0.05 significance was chosen). Intraclass correlation coefficients (ICC) were also calculated at 95% confidence interval of the ICC estimate. Microsoft Excel was also utilized to formulate Bland-Altman plots, which provide a visual representation of the mean difference between the devices.

3. Results

3.1 Inter-instrument reliability

Table 1 provides descriptive data comparing the performance of the EVJ Handgrip to the Jamar dynamometer. Intraclass correlation coefficients (ICC) compare two sets of data and determines the degree of relatedness the measurements are to each other. ICC is a “widely used reliability index in test-retest, intrarater, and interrater reliability analyses” [16]. Values between 0.75 to 0.9 indicate good reliability and values greater than 0.90 indicate excellent reliability [21]. The ICC between the two devices ranged from 0.81 to 0.84 indicating good reliability that the measures can be replicated.

3.2 Concurrent validity

Cohen’s calculations indicate a small effect size for comparison of right hand to left hand for female and male populations. The greatest difference was noted with the left hand of the female participants, though this was minor, and agreed with some female participants’ comments that discomfort with the devices may have affected their ability to provide consistent measurements. Paired $t$ -tests for female and male participants indicated no significant differences between the means of the two devices (alpha $=$ 0.05) though the results for the male right side grip measurement were not as statistically significant as the other measurements. For both devices, the means of the right-hand grip strength were between 4–8% greater than the left hand for both males and females. As 91% of females ( $N=$ 181) and 84% of males ( $N=$ 117) identified as being right hand dominant, these differences agree with Bechtol’s conclusion that the dominant hand tends to be 5–10% stronger than the nondominant hand [22].

Figure 3.

Bland-Altman plots

Figure 3 provides a graphic representation of Bland-Altman plots [17], which describes the agreement between the EVJ handgrip to the Jamar dynamometer by constructing a limit of agreement. The Bland–Altman method calculates the mean difference between two methods of measurement (the ‘bias’), and 95% limits of agreement as the mean difference (2 SD) providing a visual judgement of how well two methods of measurement agree [12]. This statistic plots the difference between both scores being compared by the mean of both scores together. The greater amount of data that falls within the two SD plot, and the tighter the data is packed, the more comparable the data is. The results indicated ninety-five percent of female right and 93% of female left measures lie within two SD of the mean difference while 94% of male right and left data points lie within two SD of the mean difference. This indicates a high confidence when comparing the two devices.

3.3 Qualitative data

In a post-participation questionnaire, participants were asked to compare the comfort of the two devices. Thirty-six percent of female participants cited the EVJ device was of greater comfort, 34% felt the Jamar was more comfortable, while 30% gave no preference. Forty percent of males felt the Jamar device was more comfortable, while 29% favored the EVJ Handgrip, and 30% had no preference. There was no consistency on which features were preferred on each device with ergonomic fit, weight, and material composition (i.e. plastic or metal) cited as common areas. For example, one participant indicated the EVJ Handgrip felt “comfortable compared to the Jamar’s handle that added additional strain when adding pressure” while another noted, “The BTE initially gave less force (at first) …but toward the end of the duration became uncomfortable. The Jamar gave equal comfort/discomfort throughout. Both were sized appropriately and easy to grasp”.

4. Discussion

Digital dynamometers may provide numerous benefits over an analog gauge, some of which include: Eliminating the need to estimate grip strength measures, increasing inter-rater reliability, and increasing sensitivity to applied force [15]. This study was focused on determining the reliability and reproducibility of the EVJ Handgrip developed by BTE Tech. by comparing its performance to the Jamar Hand Dynamometer.

The EVJ Handgrip indicated good inter-instrument reliability to the Jamar device with both male and female populations. Previous studies indicate that devices that can demonstrate equivalent measurements to the Jamar device can use published normative data in clinical use [10, 17]. Though complete agreement between the two devices was not achieved, the EVJ Handgrip demonstrates good comparability to the Jamar device, and the EVJ device utilizes a similar design and the same units of measurement (pounds or kilograms), it may be suitable that the EVJ Handgrip can use the normative data [24].

At the conclusion of the study, the Jamar devices were returned to the independent engineering firm for recalibration. The calibration report indicated that four-of-five devices required minor adjustments to return to their design specifications. The EVJ Handgrips were each run through the internal calibration process with each device indicating no need for adjustments. The degradation in the performance of the Jamar devices may have slightly affected the overall results. However, the researchers feel this was countered by using five of each device and having a large sample for the study. The need for external calibration for the Jamar devices provides an additional strength for the EVJ Handgrip which is equipped with its own calibration tools.

As previously noted, when the participants were queried regarding comfort and preference of the device, the results varied greatly. Male participants tended to prefer the fit of the Jamar Device while females preferred the EVJ Handgrip. Participants expressed varying opinions regarding the comfort of both devices, noting aspects such as weight, handle shape, handle size, and handle material.

Limitations to this study include the use of a healthy convenience population with 83% of participants between the ages of 20–29 years with no known upper extremity conditions. To ensure generalizability of the device across the lifespan, future studies are planned to include a broader age range as well as individuals with lower grip strength scores and those with disabilities affecting grip strength. Another limiting factor may have been related to participants’ feelings of discomfort when utilizing one or both devices. Participants generally expressed a preference for one device over the other, however, there was no one device that was significantly more preferred than the other. Further concern was expressed regarding the shape and material composition of each handle. The developers have been informed of these results and recommend to continue to monitor reports from clinicians and modify the grip if necessary.

Author contributions

CONCEPTION: Edwin J. Myers

PERFORMANCE OF WORK: Edwin J. Myers David S. Dominguez, Melissa E. Guigliano and Melissa G. Mallory

INTERPRETATION OR ANALYSIS OF DATA: Edwin J. Myers, David S. Dominguez, Melissa E. Guigliano and Melissa G. Mallory

PREPARATION OF THE MANUSCRIPT: Edwin J. Myers, David S. Dominguez, Melissa E. Guigliano and Melissa G. Mallory

REVISION FOR IMPORTANT INTELLECTUAL CONTENT: Edwin J. Myers

SUPERVISION: Edwin J. Myers

Ethical considerations

Approval for the study was received from the Florida Gulf Coast University Institutional Review Board and was assigned protocol #2018-28. All data collected from 2018 Apr through 2019 Dec.

Footnotes

Acknowledgments

The authors have no acknowledgments or statement of funding.

Conflict of interest

This research received no specific grant from any funding agency, commercial or not-for-profit sectors. The authors declare no conflict of interest in the completion of this study.

References

Amaral Josária

Mancini

Novo Júnior José

. Comparison of three hand dynamometers in relation to the accuracy and precision of the measurements. Rev Bras Fisioter. 2012 June [cited 2020 Nov 25]; 16(3): 216-224. Available from: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1413-35552012000300007&lng=en. doi: 10.1590/S1413-35552012000300007.

Norman

Stobaus

Gonzalez

Schulzke

Pirlich

. Hand grip strength: outcome predictor and marker of nutritional status. Clin Nutr. 2010 Apr; 30(2): 135-42. doi: 10.1016/j.clnu.2010.09.010.

Mathiowetz

Rennells

Donahoe

. Effect of elbow position on grip and key pinch strength. J Hand Surg. 1985 Sep; 10(5): 694-7. doi: 10.1016/s0363-5023(85)80210-0.

Guerra

Amaral

Sousa

Fonseca

Pichel

Restivo

. Comparison of Jamar and Bodygrip Dynamometers for handgrip strength measurement. J Strength Cond Res. 2017 Jul; 31(7): 1931-40. doi: 10.1519/JSC.0000000000001666.

Kim

Shinkai

. Prevalence of muscle weakness based on different diagnostic criteria in community-dwelling older adults: a comparison of grip strength dynamometers. Geriatr Gerontol Int. 2017 Nov; 17(11): 2089-95. doi: 10.1111/ggi.13027.

Leyk

Rohde

Erley

Gorges

Wunderlich

Rüther

Essfeld

. Recovery of hand grip strength and hand steadiness after exhausting manual stretcher carriage. Eur J Appl Physiol. 2006 Mar; 96(5): 593-9. doi: 10.1007/s00421-005-0126-0.

Fain

Weatherford

. Comparative study of Millennials’ (age 20–34 years) grip and lateral pinch with the norms. J Hand Ther. 2016 Oct/Dec; 29(4): 483-8. doi: 10.1016/j.jht.2015.12.006.

Bellace

Healy

Besser

Byron

Hohma

. Validity of the Dexter Evaluation System’s Jamar dynamometer attachment for assessment of hand grip strength in a normal population. J Hand Ther. 2000 Jan/Mar; 13(1): 46-51. doi: 10.1016/S0894-1130(00)80052-6.

Hogrel

. Grip strength measured by high precision dynamometry in healthy subjects from 5 to 80 years. BMC Musculoskelet Disord. 2015 Jun 10; 16(1): 1-11. doi: 10.1186/s12891-015-0612-4.

10.

Mathiowetz

. Comparison of Rolyan and Jamar dynamometers for measuring grip strength. Occup Ther Int. 2002; 9(3): 201-9. doi: 10.1002/oti.165.

11.

Myers

Triscari

. Comparison of the strength endurance parameters for the Baltimore Therapeutic Equipment (BTE) Simulator II and the Jamar Handgrip Dynamometer. Work. 2017; 1(57): 95-103. doi: 10.3233/WOR-172542.

12.

Myles

Cui

. Using the Bland-Altman method to measure agreement with repeated measures. British Journal of Anaesthesia. 2007; 99(3), 309-311. doi: 10.1093/bja/aem214.

13.

Trampisch

Franke

Jedamzik

Hinrichs

Platen

. Optimal Jamar dynamometer handle position to assess maximal isometric hand grip strength in epidemiological studies. J Hand Surg. 2012 Nov; 37(11): 2368-73. doi: 10.1016/j.jhsa.2012.08.014.

14.

Ugurlu

Özdogan

. Conversion of grip strength scores between Jamar dynamometer and a modified sphygmomanometer in patients with rheumatoid arthritis. Isokinet Exerc Sci. 2013 Jan; 21(4): 263-72. doi: 10.3233/IES-130493.

15.

Langer

Maeir

Michaeilevich

Luria

. Evaluating hand function in clients with trigger finger. Occup Ther Int. 2017 Jan 10; 24(1): 1-8. doi: 10.1155/2017/9539206.

16.

Allen

Barnett

. Reliability and validity of an electronic dynamometer for measuring grip strength. Int J Ther Rehabil. 2013; Aug [cited 2020 Sep15]; 18(5): 258-65. Available from: doi: 10.12968/ijtr.2011.18.5.258.

17.

Bland

Altman

. Agreement between methods of measurement with multiple observations per individual. J Biopharm Stat. 2007 Jul 5; 17(4): 571-82. doi: 10.1080/10543400701329422.

18.

King

. Interinstrument reliability of the Jamar electronic dynamometer and pinch gauge compared with the Jamar hydraulic dynamometer and B&L Engineering mechanical pinch gauge. Am J Occup Ther. 2013 Jul/Aug; 67(4): 480-3. doi: 10.5014/ajot.2013.007351.

19.

Donovan

Maher

Yoon

Mendonca

. Reliability of the bulb dynamometer for assessing grip strength. Open J Occup Ther. 2018 Spring; 6(2). doi: 10.15453/2169-6408.1404.

20.

Sammons Preston Roylan (pub). Jamar Hand Dynamometer owner’s manual. date unknown [cited 2020 Nov 20]. Available from: https//www.jlwinstruments.com/files/1413/6502/5788/JamarInstructionManual.pdf.

21.

Roberts

Denison

Martin

Patel

Syddall

Cooper

, et al. A review of the measurement of grip strength in clinical and epidemiological studies: towards a standardised approach. Age Ageing. 2011 Jul; 40(4): 423-9. doi: 10.1093/ageing/afr051.

22.

Hepping

Ploegmakers

Geertzen

Bulstra

Stevens

. Influence of hand preference on grip strength in children and adolescents; A cross-sectional study of 2284 children and adolescents. PLoS One. 2015 Nov; 23(10). doi: 10.1371/journal.pone.0143476.

23.

Koo

. A guideline of selecting and reporting intraclass correlation coefficients for reliability research. J Chiropr Med. 2016 Jun; 15(2): 155-63. doi: 10.1016/j.jcm.2016.02.012.

24.

Mathiowetz

Vizenor

Melander

. Comparison of Baseline instruments to the Jamar dynamometer and the B & L Engineering pinch gauge. OTJR. 2000 Jul 1; 20(3): 147-62. doi: 10.1177/153944920002000301.

Comparison of the BTE tech EVJ handgrip to the Jamar hand dynamometer for measuring grip strength

Abstract

INTRODUCTION:

METHOD:

RESULTS:

CONCLUSIONS:

Keywords

1. Introduction

2. Methods

2.1 Design

2.2 Participants

Table 1 Performance comparison of the BTE EVJ Handgrip to the Jamar Hand Dynamometer for females ( n = 199) and males ( n = 139). All measurements recorded in kilograms

2.5 Data analysis

3. Results

3.1 Inter-instrument reliability

3.2 Concurrent validity

4. Discussion

Author contributions

Ethical considerations

Footnotes

Acknowledgments

Conflict of interest

References

Table 1
Performance comparison of the BTE EVJ Handgrip to the Jamar Hand Dynamometer for females ( $n=$ 199) and males ( $n=$ 139). All measurements recorded in kilograms