Revised normative values for grip strength with the Jamar dynamometer

Authors

  • Martine J. H. Peters,

    1. Department of Neurology, Maastricht University Medical Centre, Maastricht, The Netherlands
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  • Sonja I. van Nes,

    1. Department of Neurology, Erasmus Medical Centre Rotterdam, Rotterdam, The Netherlands
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  • Els K. Vanhoutte,

    1. Department of Neurology, Maastricht University Medical Centre, Maastricht, The Netherlands
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  • Mayienne Bakkers,

    1. Department of Neurology, Maastricht University Medical Centre, Maastricht, The Netherlands
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  • Pieter A. van Doorn,

    1. Department of Neurology, Erasmus Medical Centre Rotterdam, Rotterdam, The Netherlands
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  • Ingemar S. J. Merkies,

    1. Department of Neurology, Maastricht University Medical Centre, Maastricht, The Netherlands
    2. Department of Neurology, Erasmus Medical Centre Rotterdam, Rotterdam, The Netherlands
    3. Department of Neurology, Spaarne Hospital, Hoofddorp, The Netherlands
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  • Catharina G. Faber,

    Corresponding author
    1. Department of Neurology, Maastricht University Medical Centre, Maastricht, The Netherlands
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  • on behalf of the PeriNomS Study group

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    • Members of the PeriNomS Studygroup: Dr. A. A. Barreira, Brazil; Dr. D. Bennett, UK; Prof. L. H. van den Berg, The Netherlands; Prof. P. Y. K. van den Bergh, Belgium; Prof. V. Bril, Canada; Prof. D. R. Cornblath, USA; Prof. M. Dalakas, USA; Dr. G. Devigili, Italy; Prof. P. A. van Doorn, The Netherlands; Dr. C. G. Faber, The Netherlands; Prof. M. A. Fisher, USA; Dr. K. C. Gorson, USA; Dr. R. D. Hadden, UK; Prof. A. F. Hahn, Canada; Prof. H-P Hartung, Germany, Prof. R. A. C. Hughes, UK; Prof. I. Illa, Spain; Dr. H. Katzberg, Canada; Prof. B. C. Kieseier, Germany; Dr. A. J. van de Kooi, The Netherlands; Dr. G. Lauria, Italy; Prof. J-M. Léger, France; Prof. R. A. Lewis, USA; Dr. M. P. T. Lunn, UK; Dr. I. S. J. Merkies, The Netherlands; Prof. E. Nobile-Orazio, Italy; Dr. N. C. Notermans, The Netherlands; Dr. L. Padua, Italy; Prof. J. Pouget, France; Dr. M. M. Reilly, UK; Dr. B. Smith, USA; Prof. M. de Visser, The Netherlands; Dr. D. Walk, USA.


Catharina G. Faber, MD, PhD, Department of Neurology, Maastricht University Medical Center, PO Box 5800, 6202 AZ Maastricht, The Netherlands. Tel: +31-64-6427-603; Fax: +31-43-3877-055; E-mail: c.faber@mumc.nl

Abstract

The Jamar dynamometer has been widely used in various chronic illnesses and has demonstrated its strength as a potential prognostic indicator. Various stratified normative values have been published using different methodologies, leading to conflicting results. No study used statistical techniques considering the non-Gaussian distribution of the obtained grip strength (GS) values. Jamar GS was assessed in 720 healthy participants, subdivided into seven age decade groups consisting of at least 50 men and 50 women each. Normative values (median and fifth values) were calculated using quantile regressions with restricted cubic spline functions on age. Possible confounding personal factors (hand dominance, length, weight, hobby, and job categorization) were examined. Clinically applicable revised normative values for the Jamar dynamometer, stratified for age and gender, are presented. Hand dominance had no influence. Other personal factors only minimally influenced final values. This study provides revised normative GS values for the Jamar dynamometer.

Introduction

Distal weakness generally predominates in patients with polyneuropathy and may contribute to deficits in daily activities and social participation (Kleyweg et al., 1991; Merkies et al., 2000). Therefore, reliable assessment of grip strength (GS) is very important to capture clinical changes in interventional studies in these disorders. Assessment of GS has also demonstrated to be a prognostic indicator of clinical and functional recovery in other diseases affecting hand function (Langhammer et al., 2007; Formsma et al., 2008). Two devices are used widespread, the Vigorimeter and the Jamar dynamometer. Normative values for the Vigorimeter have been published using new statistical techniques (Merkies et al., 2000). Various stratified normative values for the Jamar dynamometer have been published; however, using different methodologies leads to conflicting results. No information has been provided regarding the statistical analyses for the first report on normative values for the Jamar (Mathiowetz et al., 1984). In a descriptive meta-analysis, means and 95% confidence intervals of normative values per age category were listed (Bohannon et al., 2006). Unfortunately, the methodology among the 12 recruited studies differed substantially, making the proposed normative values not suitable. In a recent study, the reported normative values were based on means (+SD), while the normative values seemed quite skewed showing a curvilinear relationship to age (Werle et al., 2009). On the basis of these observations, we examined a large cohort of healthy individuals from 20 to 96 years of age to obtain revised normative values for the Jamar dynamometer using statistical techniques that capture the non-Gaussian distribution of the obtained GS values.

Patients and Methods

A total of 720 healthy participants (20–96 years) were recruited from university, hospital and secondary school personnel, homes for the elderly and sports clubs. They volunteered on locally spread pamphlets requesting participation and were stratified for age and gender forming seven age decade groups (20–29, 30–39, …, ≥80 years), each consisting of 50 men and 50 women. Inclusion criteria were: independence in daily living, absence of any impairment affecting upper limb function (e.g., joint deformities), absence of impaired sensory function (e.g., burning, tingling, numbness of hands or feet), no concomitant disease or medication possibly causing polyneuropathy (e.g., diabetes mellitus, chemotherapy). All participants were neurologically examined with emphasis on upper extremity function and signs of peripheral nervous system deficits [e.g., muscle strength; Medical Research Council (MRC) grading], tendon reflexes, light touch, pin-prick, vibration sense (Rydel-Seiffer tuning fork) (Martina et al., 1998). Eligibility was obtained if examination was normal.

Assessment tools

The portable Jamar hydraulic hand dynamometer (Sammons Preston, Rolyan, Bolingbrook, IL, USA) was used, with the second handle position for all subjects. The presented scores are expressed in pounds force.

Test procedures

The local Medical Ethics Committee approved the protocol. All participants gave written informed consent. Through interview we collected anthropometric data (body length and weight) and hand dominance. Participants were requested to categorize their profession and hobby as being physically light (coded: 0), moderate (1), or heavy (2), if applicable.

The Jamar dynamometer was placed in the right or left hand randomly and was held loosely around the readout dial by the examiner to prevent dropping (Mathiowetz et al., 1984). In alternating order, three maximum voluntary GS contractions were taken for each hand. The mean value of each hand was used for analysis (Mathiowetz, 1990). All participants were examined in a standardized position (American Society of Hand Therapists, 1992).

Statistics

After stratification for age and gender, revised normative values (median and 0.05 quantile values, corresponding to a specificity of 95%) for the Jamar dynamometer were calculated using quantile regression analyses with restricted cubic spline functions on age (Gould and Rogers, 1994). In each gender, multivariate quantile regression analyses were performed, with length, weight, categorization of profession and hobby as the independent variables on the calculated 5th quantile normative values (dependent variable) (Herndon and Harrell, 1990; Gould and Rogers, 1994; Merkies et al., 2000). All analyses were performed using STATA 11.0 for Windows.

Results

Descriptive data of all 720 participants are presented in Table 1. Males were generally stronger than females. There was a significant curvilinear age-dependent decrease of normative values in both genders. Maximum median GS was reached among women aged 30–39 and among men aged 40–49. Furthermore, no significant difference in GS between the dominant and non-dominant hand was found (overall median difference of 1 pound). Therefore we developed one normative values graph for both hands for each gender separately (Fig. 1; Table 2).

Table 1.  Descriptive data of healthy participants.
 MaleFemaleTotal
Participants, no.365355720
Age   
 Mean (SD)55.1 (20.5)54.7 (21.1)54.9 (20.8)
 Range (year)20–9620–9520–96
Hand dominance   
 Right (%)879088
 Left (%)1078
 Ambidextrous (%)433
Length   
 Mean, in cm (SD)179 (8.3)166 (7.1)173 (10.1)
 Range (cm)150–202140–184140–202
Weight   
 Mean, in kg (SD)82.1 (12.9)68.2 (12.4)75.2 (14.4)
 Range (kg)45–13543–12343–135
Profession categorization   
 Light, no. (%)136 (37.3)115 (32.4)251 (34.9)
 Moderate, no. (%)83 (22.7)95 (26.8)178 (24.7)
 Heavy, no. (%)23 (6.3)25 (7.0)48 (6.7)
 Not applicable, no. (%)123 (33.7)120 (33.8)243 (33.8)
Hobby categorization   
 Light, no. (%)163 (44.66%)197 (55.49%)360 (50.00%)
 Moderate, no. (%)171 (46.85%)143 (40.28%)314 (43.61%)
 Heavy, no. (%)31 (8.49%)15 (4.23%)46 (6.39%)
Figure 1.

Revised grip strength values with the Jamar dynamometer for the dominant and non-dominant hands combined in healthy females (a) (n = 355, 90.1% right-handed and males (b) (n = 365, 86.6% right-handed). The upper lines in each graph correspond to the calculated median GS values. The lower lines in each graph represent the 0.05 quantile reference values. These values were obtained in each gender separately using quantile regressions with restricted cubic spline functions. Note: the y-axis for men and women differ.

Table 2.  Normative grip strength values for the Jamar dynamometer for clinical use (in pounds).
Age (years)Females (n = 355)Males (n = 365)
Number of subjectsFifth percentile Jamar values (pounds)Median Jamar values (pounds)Number of subjectsFifth percentile Jamar values (pounds)Median Jamar values (pounds)
20–295150625081100
30–395049645180105
40–495048635078107
50–595145615473104
60–69494056586495
70–79503246505177
≥80542234523454

Multivariate regression analysis did not show any significant impact of length, weight, profession or hobby categorization on the fifth percentile cut-off normative values in women. In men, only hobby categorization was related to the fifth percentile cut-off normative values; however, explaining only a small portion of 7% (p = 0.008).

Discussion

This study provides revised normative values for the Jamar dynamometer in adults. We used robust statistical techniques to present the correlation between age and GS values (Gould and Rogers, 1994). Normative values for the Jamar dynamometer have been provided before (Mathiowetz et al., 1984; Harkonen et al., 1993; Massy-Westropp et al., 2004; Bohannon et al., 2006; Werle et al., 2009). Unfortunately, all these values were obtained by calculating means of sequential age portions, without taking into account the non-Gaussian distribution of the obtained GS values, as recommended for these kinds of continuous data (Herndon and Harrell, 1990; Gould and Rogers, 1994; Merkies et al., 2000).

GS showed a curvilinear relationship to age (Mathiowetz et al., 1984; Massy-Westropp et al., 2004; Werle et al., 2009). In both genders, a marked decline of GS was seen after 60 years of age, which is in conformity with earlier reports (Mathiowetz et al., 1984; Werle et al., 2009). Our data showed hardly any difference in GS between the dominant and non-dominant hand, which is in contrast with earlier papers reporting up to 33% difference (Mathiowetz et al., 1984; Werle et al., 2009). A difference in statistical approach could be an explanation for the obtained differences.

At a workshop on outcome measures in immune-mediated neuropathies, it was argued whether the Vigorimeter, with its soft-squeezing bulb and particularly used in Europe, would have a preference over the Jamar dynamometer, mainly used in the United States (Merkies and Lauria, 2006). At the current stage, there is no consensus regarding which instrument should be used. Therefore, a comparison study of these two instruments is warranted, focusing primarily on their responsiveness findings and on patients' preference. These efforts are currently being undertaken as part of an international, multi-centre collaborative study (Peripheral Neuropathy Outcome Measures Standardization (PeriNomS) study).

Our calculated 5th percentile normative cut-off GS data did not show any correlation with parameters like weight, height, occupation, except for hobby categorization in males, which is in contrast with recent literature (Werle et al., 2009; Angst et al., 2010). However, the studies by Werle et al. and Angst et al. have used a different approach: they have calculated a correlation between the obtained raw GS scores and other parameters (height, weight, occupation) and have not used a cut-off score for these normative values, which may explain the differences with our paper (Werle et al., 2009; Angst et al., 2010). In conclusion, the current study provides robust clinically applicable normative 5th percentile GS values for the Jamar dynamometer.

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