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Abstract

BACKGROUND:

There are controversies regarding the optimal number of trials and intervals during required for testing of maximal handgrip strength.

OBJECTIVES:

To verify the minimum optimal number of trials (two versus three consecutive trials) and inter-effort interval (15, 30, 45 and 60-s) during the measurement of maximal handgrip strength.

METHODS:

One hundred healthy subjects, 51 males and 49 females, were enrolled. During the measurement of maximal handgrip strength, two consecutive trials were hypothesized to be the minimum necessary. We compared the maximal handgrip strengths between two and three consecutive trials at four different intervals (15, 30, 45, and 60-s).

RESULTS:

Irrespective of hand dominance, maximal handgrip strength was best measured with three consecutive trials rather than two at each interval (all $p<$ 0.05 except 15-s intervals with the dominant hand). The values at 60-s interval (dominant hands: 40.6 kgf, non-dominant hands: 36.7 kgf) were significantly higher than at other intervals (all $p<$ 0.05).

CONCLUSIONS:

Three consecutive trials with a 60-s interval might be the minimum needed for optimal measurement of maximal handgrip strength.

Keywords

Hand grip grip strength test trial interval

1. Introduction

Maximal handgrip strength is the maximal static strength generated by the proximal and middle phalanges of the hands [1]. It has been accepted as a reflection of general muscle strength as well as upper extremity strength and is used as a parameter reflecting general health [2, 3, 4]. Sarcopenia can be easily diagnosed with the measurement of handgrip strength [5]. It can also be a predictor of mortality, fragility, risk of falls and functional decline [6, 7, 8, 9, 10]. It can also be used as an indicator of disease activity in rheumatoid arthritis patients and as a nutritional index [11].

Due to the above characteristics of handgrip strength, some large-scale epidemiologic studies have investigated the measurement of handgrip strength [12, 13, 14]. However, handgrip strength is affected by several factors and measurement reliability could be a matter of concern. The handle position of the dynamometer [15], upper body posture [16], grip span [17], the amount of verbal instructions given by the examiner [18], time of day and muscle warm-up [19] are considered to influence test results. Also, the number and interval between trials might affect the results of handgrip strength, especially in a large-scale epidemiologic study due to the burden on examiners. After the American Society of Hand Therapists (ASHT) introduced the widely accepted concept of repetition and interval between trials, i.e. three trials with a 60-s interval, several literatures on hand grip strength have adopted this method [20, 21, 22, 23]. However, several epidemiologic studies have been performed with fewer than three trials and a less than the 60-s interval [24, 25, 26].

To reduce the burden of epidemiologic studies, we hypothesized that less than three consecutive trials with a less than 60-s interval might be appropriate and acceptable. Thus, the aim of this study was to identify the minimum optimal number of grip trials and the interval between each during the measurement of maximal handgrip strength. To this end, we compared maximal handgrip strength obtained in two compared to three consecutive trials.

2. Method

This study was approved by the Institutional Review Board of Myongji Hospital, and all subjects signed written informed consent before participating in the study.

2.1 Subjects

A total of 107 subjects (52 males [height; mean 169.4 (SD 8.5), weight; mean 64.1 (SD 11.8)], 55 Females [height; mean 159.6 (SD 7.6), weight; mean 57.1 (SD 9.1)], mean age: 31.9 years, range 23–49 years), medical personnel, were assessed for their eligibility for inclusion in this study. Every subject in this study was involved in a medium level of occupational demand according to the five categories of the Dictionary of Occupational Titles which are sedentary, light, medium, heavy and very heavy [27]. Exclusion criteria were osteoarthritis, rheumatoid arthritis ( $n=$ 1) or any other inflammatory arthritis of the upper extremities, a previous history of trauma ( $n=$ 2) or surgery on the upper extremities, any neurological disease such as carpal tunnel syndrome ( $n=$ 1), cubital tunnel syndrome, cervical radiculopathy or myelopathy, upper extremity tendinopathy ( $n=$ 1), loss of follow-up during four days of consecutive measurements ( $n=$ 2) and limited range of hand motion due to unknown causes. Finally, one hundred healthy subjects, 51 males and 49 females, mean age 32.1 (SD 6.9) y, were enrolled.

Figure 1.

The pathway to determine the minimum optimal number of trials and interval.

Figure 2.

Comparison of maximal hand grip strength between two consecutive and three consecutive trials at each interval (15, 30, 45, and 60-s) in the dominant hand.

2.2 Dynamometer and position

Maximal handgrip strength was measured with a Takei digital handgrip dynamometer (Takei T.K.K 5401, Takei Scientific Instruments Co. Ltd. Niigata, Japan). The reliability of the Takei dynamometer has been demonstrated previously [28, 29]. Handgrip strength was recorded in kilograms (kgf). The handgrip span on the dynamometer was adjusted according to each subject’s hand span, which ranged from 6 to 8 cm during the measurements. The subject was seated on a chair and the position of the upper extremity to be assessed was as follows: the shoulder was in adduction, the elbow was flexed to 90 degrees, the forearm was in neutral supination/pronation, and the wrist was in neutral to 30 degrees of volar flexion as well as in zero to 30 degrees of ulnar deviation. Subjects were instructed to maintain voluntary grip for 4 seconds. Therefore, the nature of grip strength in this study was considered to be static rather than dynamic.

Figure 3.

Maximal handgrip strength for the minimum optimal number of trials (three consecutive trials) at 60-s compared to other intervals (15, 30 and 45-s intervals) in the dominant hand.

Figure 4.

Distribution of subjects with maximal handgrip strength according to trials with a 60-s interval (4A: Dominant hand, 4B: Non-dominant hand).

2.3 Measurement

To verify the minimum optimal interval between trials, 15, 30, 45 and 60-s intervals between grips were measured. Thus, for each interval, three consecutive trials of the measurement were performed. One rest day was allowed between each time interval. We performed measurements between 17:00 and 19:00 hours to exclude the possibility of diurnal measurement variation. We assessed the dominant hand first and then the non-dominant hand in that order, and true hand dominancy was re-evaluated after measurements to rule out the possibility of the 10% rule of hand dominance [30]. The minimum optimal number of trials for each interval was determined by comparing maximal handgrip strength in two and three consecutive trials. Then the values for the minimum optimal number of trials at each interval were compared to one another (Fig. 1).

2.4 Sample size calculation

A pilot study with 15 subjects (male: 8) showed a difference of 2 kgf in mean grip strength with a standard deviation of 7 kgf. Considering the type I error as 0.05 and the type II error as 20%, the sample size was calculated as 97. We added 10% to the number of subjects (10) to compensate for the loss of data. One hundred seven subjects were scheduled to be enrolled in this study.

2.5 Statistical analyses

All statistical analyses were performed using the SPSS software package version 18.0 (SPSS, Chicago, IL, USA). The main hypothesis of this study was that two consecutive trials with a 15-s interval would be the minimum necessary to obtain maximal handgrip strength. We compared the maximal handgrip strength between two and three consecutive trials at four different intervals (15, 30, 45, and 60-s) using paired t-tests. After determining the minimum optimal number of trials at each interval, the comparisons between values for each interval were evaluated with paired t-tests. We also performed the subgroup analysis with the gender to prove the basic hypothesis of this study that gender could not affect the result of the study. Paired t-tests were also used to demonstrate this hypothesis regarding the gender subgroup analysis. A $p$ -value $<$ 0.05 was considered to indicate statistical significance.

3. Results

3.1 Dominant hand

Maximal handgrip strength during three consecutive trials at each interval were higher than the first two consecutive trials (15-s; 39.5 (SD 9.7) kgf vs 39.6 (SD 9.7) kgf, $p=$ 0.320: 30-s; 38.0 (SD 10.4) kgf vs 39.1 (SD 10.4) kgf, $p=$ 0.000: 45-s; 38.1 (SD 10.0) kgf vs 38.7 (SD 9.7) kgf, $p=$ 0.000: 60-s; 40.2 (SD 9.9) kgf vs 40.6 (SD 9.9) kgf, $p=$ 0.001) (Fig. 2). Based on the above results, the minimum optimal number of trials was determined to be three consecutive trials. The maximum handgrip strength at 60-s intervals was superior compared to the others (15-s; $p=$ 0.012, 30-s; $p=$ 0.002, 45-s; $p=$ 0.000) (Fig. 3). According to the distribution of maximal handgrip strength in subjects at a 60-s interval, 14% of the subjects showed maximal handgrip strength in the third trial (Fig. 4).

3.2 Non-dominant hand

Maximal handgrip strength during three consecutive trials at each interval were higher than two consecutive trials (15-s; 34.4 (SD 8.8) kgf vs 34.6 (SD 8.7) kgf, $p=$ 0.012: 3-s; 34.9 (SD 8.7) kgf vs 35.8 (SD 9.0) kgf, $p=$ 0.000: 45-ss; 34.1 (SD 8.3) kgf vs 34.3 (SD 8.2) kgf, $p=$ 0.009: 60-s; 36.6 (SD 8.7) kgf vs 36.7 (SD 8.7) kgf, $p=$ 0.039) (Fig. 5). Based on the above results, the minimum optimal number of trials was determined to be three consecutive trials. The maximum handgrip strength at 60-s intervals was superior compared to the others (all $p=$ 0.000) (Fig. 6). According to the distribution of maximal handgrip strength in subjects at a 60-s interval, 7% of the subjects showed maximal handgrip strength in the third trial (Fig. 4).

3.3 Subgroup analysis with the gender

We observed that the gender factor in this study did not affect the main result of a minimum optimal number of trials and intervals, supporting previous findings by Watanabe et al. [22]. The minimum optimal number of trials was determined to be three consecutive trials at 60-s intervals in each gender’s dominant hands (all $p<$ 0.05), although two consecutive trials were not inferior to three consecutive trials in nondominant hands (all $p>$ 0.05) (Table 1).

Table 1
Subgroup analysis according to the gender comparing handgrip strength between two consecutive trials and three consecutive trials with every interval (15, 30, 45 and 60-s)

Gender	Age (SD)	Dominance	Maximal handgrip strength	Maximal handgrip strength	$p$ value
		of hand	during two trials (kgf)	during three trials (kgf)
Males ( $n=$ 51)	33.8 (6.9)	Dom	48.7	49.1	0.013
		Nondom	38.2	38.3	0.083
Females ( $n=$ 49)	29.8 (6.2)	Dom	31.3	31.6	0.025
		Nondom	34.9	35	0.162

SD: Standard deviation. Dom – dominant, Nondom – nondominant, The maximal handgrip strength was measured at 60-s interval and revealed to be superior to other intervals ( $p=$ 0.000).

Figure 5.

Comparison of maximal hand grip strength between two and three consecutive trials at each interval (15, 30, 45, and 60-s) in the non-dominant hand.

Figure 6.

Maximal handgrip strength for the minimum optimal number of trials (three consecutive trials) at 60-s compared to other intervals (15, 30 and 45-s intervals) in the non-dominant hand.

4. Discussion

According to the current study results, three consecutive trials with a 60-s interval should be performed to identify maximal handgrip strength. This result could be applied in population-based studies regardless of hand dominancy. We observed that 7% to 14% of subjects by hand dominance showed maximal handgrip strength in the third trial, and this might result in the need for three rather than two consecutive trials.

The measurement of handgrip strength as one of the assessment tools for the national health index might be important to develop future nationwide health policy [6, 8, 31, 32]. However, there still are some debates about the optimum number of consecutive trials among several epidemiologic studies [2, 22, 24, 25, 33, 34]. In fact, the hand grip strength in subjects above 19 years of age has been measured biennially since 1989 for the Korean National Fitness Assessment (KNFA) [12]. However, this measurement was performed on two consecutive occasions with no rest period between trials. According to the NHANES (National Health Assessment and Nutrition Examination Survey) in the United States of America, the annual measurements of handgrip strength in subjects above six years of age have been performed by conducting three consecutive trials with a 60-s interval between each trial [13]. A 60-s rest between trials has been known to control for the confounding effect of fatigue on results, and in some subjects maximal handgrip strength was measured in the third trial, as in our study [21]. Some of the previous studies recommended a long rest between trials [23, 35, 36, 37]. However, the measurement of handgrip strength in a large population could be time-consuming and might cause some burden on the examiners due to the large number of trials and long inter-trial intervals. Also, Trossman et al. reported that there were no differences among 15, 30, or 60-s rests between trials during the measurement of handgrip strength [21]. Therefore, trials with a small inter-trial interval could be worth performing. However, we found that three trials with a 60-s inter-trial interval showed significantly higher values of maximal handgrip strength than a fewer number of trials with a small inter-trial time interval. In this study, we aimed to compare the 45-s interval, which has not been evaluated in previous studies, with other interval lengths. We found that measurements of handgrip strength with a 45-s interval were always lower than those with a 60-s interval.

Mathiowetz [34] suggested that three attempts could lead to learning effects and adaptation. Assessment of grip strength may be the first experience for some people and may need adjustment for learning. Coordination and learning of short-term motor skills can take several minutes, which may be achieved through spatial working memory [38]. The current results likely reflect coordination and learning of short-term motor skills.

This study had several limitations. First, it is based on healthy subjects and not on patients with chronic disease or sarcopenia whose results might contribute to non-standard outcomes. Second, we did not examine the efficacy of more than three trials and a more than 60-s interval compared to three trials with a 60-s interval. Third, subjects’ level of physical activity was not meticulously controlled although a medium occupational demand was identified in every subject.

The strengths of this study were as follows: First, it was a study in a large number of subjects. Second, a 45-s rest between trials was first adopted, and it proved to be inferior to a 60-s rest. Third, we tried to rule out as many factors as possible that might affect handgrip strength. Fourth, we suggested the possibility of adaptation of short-term motor skills as well as the fatigue theory for the superiority of three trials with a 60-s interval. Finally, we emphasized the need for sufficient trials with a sufficient time interval in epidemiologic studies, which should not be influenced by timeserving.

5. Conclusion

For the measurement of maximal handgrip strength, 3 consecutive trials with a 60-s interval is optimal, although it is more time consuming.

Footnotes

Conflict of interest

The authors declared no conflict of interest.

References

Freivalds

. Tool evaluation and design. in: Bhattacharya

McGlothlin

. Occupational Ergonomics: Theory and Applications, New York, NY, USA: Marcel Dekker Inc.; 1996. p. 303-327.

Roberts

Denison

Martin

, et al. A review of the measurement of grip strength in clinical and epidemiological studies: Towards a standardised approach. Age Ageing 2011; 40: 423-9.

Jones

. The assessment of hand function: A critical review of techniques. J Hand Surg Am 1989; 14: 221-8.

Bohannon

. Hand-grip dynamometry predicts future outcomes in aging adults. J Geriatr Phys Ther 2008; 31: 3-10.

Cruz-Jentoft

Baeyens

Bauer

, et al. Sarcopenia: European consensus on definition and diagnosis: Report of the European Working Group on Sarcopenia in Older People. Age Ageing 2010; 39: 412-23.

Syddall

Martin

Harwood

Cooper

Aihie Sayer

. The SF-36: A simple, effective measure of mobility-disability for epidemiological studies. J Nutr Health Aging 2009; 13: 57-62.

Kerr

Syddall

Cooper

Turner

Briggs

Sayer

. Does admission grip strength predict length of stay in hospitalised older patients? Age Ageing 2006; 35: 82-4.

Gale

Martyn

Cooper

Sayer

. Grip strength, body composition, and mortality. Int J Epidemiol 2007; 36: 228-35.

Cooper

Kuh

Hardy

. Objectively measured physical capability levels and mortality: systematic review and meta-analysis. BMJ 2010; 341: c4467.

10.

Sayer

Syddall

Martin

Dennison

Anderson

Cooper

. Falls, sarcopenia, and growth in early life: Findings from the Hertfordshire cohort study. Am J Epidemiol 2006; 164: 665-71.

11.

Rhind

Bird

Wright

. A comparison of clinical assessments of disease activity in rheumatoid arthritis. Ann Rheum Dis 1980; 39: 135-7.

12.

KISS (Korea Institute of Sport Science) Korean National Fitness Assessment. Sejong-si (Korea): Ministry of Culture, Sports and Tourism, 2015. http://www.mcst.go.kr/web/s_data/dataMain.jsp (date accessed).

13.

CDC (Centers for Disease Control and Prevention) National Health and Nutrition Examination Survey, GA, USA: US Department of Health and Human Services, 2015. http://www.cdc.gov/nchs/nhanes/index.htm.

14.

MEXT (Ministry of Education, Culture, Sports, Science and Technology, Japan) 2013 Physical Fitness and Motor Skills Test Overview, Tokyo (JP): Ministry of Educaton, Cluture, Sports, Science and Technology, Japan, 2013. http://www. mext.go.jp/english/topics/1359170.htm (date accessed).

15.

Trampisch

Franke

Jedamzik

Hinrichs

Platen

. Optimal Jamar dynamometer handle position to assess maximal isometric hand grip strength in epidemiological studies. J Hand Surg Am 2012; 37: 2368-73.

16.

Lin

Chien

Cheng

Sung

. Grip strength in different positions of elbow and shoulder. Arch Phys Med Rehabil 1994; 75: 812-5.

17.

Blackwell

Kornatz

Heath

. Effect of grip span on maximal grip force and fatigue of flexor digitorum superficialis. Appl Ergon 1999; 30: 401-5.

18.

Johansson

Kent

Shepard

. Relationship between verbal command volume and magnitude of muscle contraction. Phys Ther 1983; 63: 1260-5.

19.

Peolsson

Hedlund

Oberg

. Intra- and inter-tester reliability and reference values for hand strength. J Rehabil Med 2001; 33: 36-41.

20.

Patterson

Baxter

. A multiple muscle strength testing protocol. Arch Phys Med Rehabil 1988; 69: 366-8.

21.

Trossman

P-W

. The effect of the duration of intertrial rest periods on isometric grip strength performance in young adults. The Occupational Therapy Journal of Research 1989; 9: 362-378.

22.

Watanabe

Owashi

Kanauchi

Mura

Takahara

Ogino

. The short-term reliability of grip strength measurement and the effects of posture and grip span. J Hand Surg Am 2005; 30: 603-9.

23.

Fess

. Grip Strength, 2nd edition. Chicago: American Society of Hand Therapists; 1992.

24.

Hanten

Chen

Austin

, et al. Maximum grip strength in normal subjects from 20 to 64 years of age. J Hand Ther 1999; 12: 193-200.

25.

Werle

Goldhahn

Drerup

Simmen

Sprott

Herren

. Age- and gender-specific normative data of grip and pinch strength in a healthy adult Swiss population. J Hand Surg Eur Vol 2009; 34: 76-84.

26.

Harth

Vetter

. Grip and pingh strength among selected adult occupational groups. Occup Ther Int 1994; 1: 13-28.

27.

Dictionary of Occupational Titles. Online Version for Windows. 4th edition. Washington, DC, USA: United States Department of Labor Employment and Training Administration; 1991.

28.

Anumula

Beku

Murthy

YSN

. Measurement of reliability in grip strength. Indian Journal of Physiotherapy and Occupational Therapy 2014; 8(2): 115-119.

29.

Cadenas-Sanchez

Sanchez-Delgado

Martinez-Tellez

, et al. Reliability and validity of different models of TKK hand dynamometers. Am J Occup Ther 2016; 70: 7004300010.

30.

Petersen

Petrick

Connor

Conklin

. Grip strength and hand dominance: Challenging the 10% rule. Am J Occup Ther 1989; 43: 444-7.

31.

Sasaki

Kasagi

Yamada

Fujita

. Grip strength predicts cause-specific mortality in middle-aged and elderly persons. Am J Med 2007; 120: 337-42.

32.

Rantanen

Era

Heikkinen

. Maximal isometric strength and mobility among 75-year-old men and women. Age Ageing 1994; 23: 132-7.

33.

Shim

Roh

Kim

, et al. Normative measurements of grip and pinch strengths of 21st century korean population. Arch Plast Surg 2013; 40: 52-6.

34.

Mathiowetz

. Effects of three trials on grip and pinch strength measurement. J Hand Ther 1990; 4: 195-198.

35.

Jackson

Watkins

Patton

. A factor analysis of twelve selected maximal isotonic strength performances on the universal gym. Med Sci Sports Exerc 1980; 12: 274-7.

36.

Koller

Kase

. Muscle strength testing in Parkinson’s disease. Eur Neurol 1986; 25: 130-3.

37.

Ohtsuki

. Decrease in grip strength induced by simultaneous bilateral exertion with reference to finger strength. Ergonomics 1981; 24: 37-48.

38.

Seidler

Anguera

. Neurocognitive contributions to motor skill learning: The role of working memory. J Mot Behav 2012; 44: 445-53.

Minimum optimal trials and interval during measurement of maximal handgrip strength

Abstract

BACKGROUND:

OBJECTIVES:

METHODS:

RESULTS:

CONCLUSIONS:

Keywords

1. Introduction

2. Method

2.1 Subjects

2.4 Sample size calculation

2.5 Statistical analyses

3. Results

3.1 Dominant hand

3.2 Non-dominant hand

3.3 Subgroup analysis with the gender

Table 1 Subgroup analysis according to the gender comparing handgrip strength between two consecutive trials and three consecutive trials with every interval (15, 30, 45 and 60-s)

5. Conclusion

Footnotes

Conflict of interest

References

Table 1
Subgroup analysis according to the gender comparing handgrip strength between two consecutive trials and three consecutive trials with every interval (15, 30, 45 and 60-s)