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Abstract

Background:

Static grip strength has been a reliable method for assessing the functional capacity of the individual and can be a useful marker for identifying elderly people at risk of functional deterioration leading to a fall. However, static grip strength alone may not represent the true maximum strength that an individual could exert in his/her daily life, especially if the task requires simultaneous forces from gripping and a forearm twisting action, which is termed as functional isometric grip strength. Hence, the objectives of this study were to determine the differences in the fallers’ grip strengths at static-neutral grip position and during isometric forearm pronation/supination, as well as the differences between the maximum and sustained isometric grip strengths.

Methods:

Data were analysed from 31 elderly people (11 males and 20 females) aged 70 and over. Using a custom-made hand strength measurement device, three measurements were taken: (1) grip strength in neutral forearm position; (2) grip strength during isometric forearm pronation; and (3) grip strength during isometric forearm supination.

Results:

Elderly fallers could only achieve approximately 60%–80% of the maximum normative strength. Additionally, it was found that their functional isometric grip strengths were generally weaker than their static maximal grip strength, especially during isometric supination as either maximum or sustained isometric supination grip strengths (Dominant hand: 10.6 kg and 8.5 kg, respectively (males); 6.0 kg and 4.4 kg, respectively (females)).

Conclusion:

Elderly fallers are weaker when their grip is subjected to additional torque, endurance or both. Hence, these findings have potential implications for designing better screening tools for the geriatric population.

Keywords

Ageing elderly fallers frailty grip strength isometric strength

Introduction

Falls are one of the major concerns for the geriatric population, especially among frail elderly people, and studies have proved that falls can often lead to a poor quality of life, functional deterioration, serious injuries, disabilities, emotional distress or even death.^1–4 Furthermore, the incidence of falls is expected to rise as the population ages.^4–7 Thus, there is a constant need to improve screening tools and interventions that could assist in identifying potential fallers and preventing future and/or recurrent falls.^{2, 4}

Hand grip strength measurement has been known to be a useful tool for assessing overall muscle weakness and identifying elderly people at risk of functional deterioration or frailty.^8–13 Taekema et al. reported that lower grip strength was able to predict an accelerated decline in activities in daily living (ADL) functionality.¹¹ In a systematic review by Bohannon et al., the authors found that low grip strength was associated with a greater likelihood of functional limitations.¹² However, although static grip strength has been a reliable method for assessing the muscle strength and functional capacity of the individual, it may not represent the true maximum strength that a person could exert in his/her daily life, especially with regard to activities such as opening a jar or holding on to a grab bar during a fall, both of which involve simultaneous forces from gripping and wrist/forearm twisting action. Moreover, studies have also reported that the amount of grip strength generated is dependent on forearm muscle contraction (isometric or isotonic), and/or position of the forearm (neutral, pronated or supinated).^13–15 LaStayo et al. assessed the change in grip strength as the wrist moved from extension/radial deviation to flexion/ulnar deviation arc while simultaneously gripping the dynamometer. The authors reported that the dynamic strength was lower than the maximum static grip strength and, thus, suggested that dynamic assessment of the grip strength could better mimic functional activities.¹³ In a study by Richards et al., the authors reported that the position of the forearm could affect the grip strength generated and they found that the grip strength was the strongest at forearm supination and weakest at pronation.¹⁴ In a normative study on healthy elderly people in Singapore, the authors have reported that the grip strength decreased while simultaneously exerting isometric forearm torque in pronation or supination directions.¹⁵ These studies have demonstrated that static grip strength alone may not be sufficient to determine the functional capacity of the individual. Furthermore, in this study, we postulated that elderly fallers are not capable of achieving their maximum strength if the task requires them to co-activate both their grip and forearm forces.

In this article, we investigated the grip strengths generated while simultaneously exerting isometric forearm strengths for a period of time (10 seconds), terming the action ‘functional isometric grip strength’. The aims of this investigation were to determine the differences in the fallers’ grip strengths at static-neutral grip position and during isometric forearm pronation/supination, as well as the differences between the maximum and sustained isometric grip strengths. Additionally, we also compared the findings with the functionally independent healthy community-dwelling groups from our previous study.¹⁵

Methods

Subjects

In this study, 50 elderly patients aged 70 and over, and with a history of recurrent falls as indicated in their medical case notes, were recruited from the geriatric clinic in the Singapore General Hospital. Out of 50, only 31 participants completed all the grip strength measurements (Table 1). The remaining 19 participants were excluded from the data analysis because they were unable to complete the study either due to an inability to follow the assessor’s instructions, tiredness or because they were experiencing joint pain/discomfort.

Table 1.

Characteristics of participants – elderly fallers (total recruited: N = 50).

	Analysed	Participants excluded
Sample size [N]	31(Male: 11; Female: 20)	19(Male: 5; Female: 14)
Mean age, years (SD)	83.1 (6.1)	82.0 (7.6)
QuickDASH
Missing values	(N = 5)	(N = 5)
Mean (SD)	27.2 (22.7)	43.7 (22.9)
Barthel score
Mean (SD)	73.4 (28.0)	59.7 (29.3)
MMSE score, N (%)
Missing values	0 (0)	2 (10)
Normal cognitive (27 to 30)	4 (13)	1 (5)
Mild impairment (21 to 26)	6 (19)	2 (11)
Moderate (11 to 20)	15 (49)	7 (37)
Severe cognitive (0 to 10)	6 (19)	7 (37)
^#1 Modified Frail Index score, N (%)
No frailty (mFI = 0)	1 (3)	1 (5)
Low frailty (mFI = 1 or 2)	17 (55)	7 (37)
Intermediate frailty/Frail (mFI ⩾ 3)	13 (42)	11 (58)

: Modified Frail Index (mFI), total possible highest score is 11.

MMSE: Mini-Mental State Examination.

The control group was obtained from our previous study and only data (N = 157) that fall within the same age group (70 years old and over) were used. The subjects in the control group have a high level of independence based on the Katz Index of Independence in Activities of Daily Living (Katz ADL) scores.^{16, 17} Additionally, the subjects did not present any physical musculoskeletal conditions based on their medical history questionnaire at the time of the study.

The study procedures were approved by the SingHealth Centralized Institutional Review Board (reference number: 2016/2004). Prior to the study, informed consent was obtained from all participants.

Procedures

Prior to the grip strength measurements, the patients’ functional independence was assessed using the Barthel Index ADL¹⁸ and the QuickDASH¹⁹ score. Their cognitive function was measured using the Mini-Mental State Examination (MMSE).²⁰ Their past and current medical conditions were also recorded, and the data were used to calculate their frailty score using the Modified Frailty Index.²¹

The setup for this study has been described in our previous study.¹⁵ Briefly, as presented in Figure 1a, the subject was seated on a chair with feet planted flat on the floor, elbow flexed at 90^o and forearm in the neutral position.^22–23 Using a customized hand strength measurement device, three types of grip measurements were taken: (1) maximum sustained grip strength at neutral forearm position (i.e. static grip); (2) maximum sustained grip strength during isometric forearm pronation (i.e. isometric pronation); and (3) maximum sustained grip strength during isometric forearm supination (i.e. isometric supination).

Figure 1.

(a) Grip measurement device used. (b) Participant’s grip profile was presented as a grip over time graph.

Both hands were tested starting with the right hand. In order to avoid any inconsistency caused by fatigue, the subject was told to rest for one minute after every measurement. All measurements were taken once and 10 seconds of data were recorded for each measurement. The maximum isometric grip strength was reflected as the peak strength, whereas the sustained isometric grip strength was calculated based on the average of the 10 seconds data. The grip profile was presented as a grip over time graph as shown in Figure 1b.

Statistical methods

Continuous variables were summarized as mean and standard deviation (SD) or median as appropriate, and categorical variables by frequency (%). The Wilcoxon rank sum test was used to evaluate the differences in isometric grip strengths between fallers and healthy community-dwelling (control) groups from our previous study.¹⁵ The differences between static and isometric pronation/supination grip strengths as well as the differences between maximum and sustained isometric grip strengths among fallers were analysed using a non-parametric Wilcoxon signed-rank test and percentage (median) differences. The analyses were performed using SPSS 23. A difference was considered to be statistically significant if the p-value was less than 0.05.

Results

Comparison between elderly fallers and healthy community-dwelling elderly people

Comparing the present data with the results obtained previously,¹⁵ elderly fallers were found to be significantly weaker than the healthy community (control) group as presented in Table 2. In terms of the difference in their maximum isometric grip strengths, fallers were 30%–50% weaker than the control group, with the highest difference found during isometric supination (dominant hand). Similar results were also observed for the sustained isometric grip strengths as presented in Table 3. Although both groups exhibited lower sustained strength compared to their maximum strength, the difference between the fallers and the control group was still as significant.

Table 2.

Elderly fallers vs community controls (maximum functional isometric grip strength (mean ± SD)).

	Positions		Fallers(kg)	Controls(kg)	Difference(kg (%))	p-value(Fallers vs control)
Dominant hand	Static grip	Overall	11.6 ± 7.7	17.5 ± 7.8	5.9 (33.7)	< 0.001
		Males	17.1 ± 8.4	22.3 ± 7.5	5.2 (23.3)	0.041
		Females	8.5 ± 5.5	13.8 ± 5.8	5.3 (38.4)	< 0.001
	Isometric supination	Overall	8.2 ± 5.3	14.6 ± 6.8	6.4 (43.8)	< 0.001
		Males	11.1 ± 6.2	18.5 ± 7.2	7.4 (40.0)	0.004
		Females	6.6 ± 4.1	11.5 ± 4.7	4.9 (42.6)	< 0.001
	Isometric pronation	Overall	9.4 ± 6.5	14.5 ± 6.7	5.1 (35.2)	< 0.001
		Males	12.6 ± 7.6	18.4 ± 6.4	5.8 (31.5)	0.013
		Females	7.6 ± 5.3	11.4 ± 5.0	3.8 (33.3)	0.001
Non-dominant hand	Static grip	Overall	10.2 ± 7.3	15.3 ± 7.1	5.1 (33.3)	< 0.001
		Males	14.3 ± 8.7	20.0 ± 7.1	5.7 (28.5)	0.028
		Females	8.0 ± 5.5	11.6 ± 4.5	3.6 (31.0)	0.001
	Isometric supination	Overall	7.6 ± 5.2	12.7 ± 5.8	5.1 (40.2)	< 0.001
		Males	8.7 ± 4.9	16.2 ± 6.2	7.5 (46.3)	< 0.001
		Females	6.9 ± 5.4	10.0 ± 3.6	3.1 (31.0)	0.001
	Isometric pronation	Overall	7.7 ± 5.2	13.4 ± 6.2	5.7 (42.5)	< 0.001
		Males	9.3 ± 4.5	17.5 ± 6.0	8.2 (46.9)	< 0.001
		Females	6.8 ± 5.5	10.3 ± 4.3	3.5 (34.0)	0.001

Table 3.

Elderly fallers vs community controls (sustained functional isometric grip strength (mean ± SD)).

	Positions		Fallers(kg)	Controls(kg)	Difference(kg (%))	p-value(Fallers vs control)
Dominant hand	Static grip	Overall	9.8 ± 6.9	15.5 ± 7.5	5.7 (36.8)	< 0.001
		Males	14.4 ± 7.2	20.2 ± 7.3	5.8 (28.7)	0.021
		Females	7.3 ± 5.3	11.9 ± 5.4	4.6 (38.7)	0.001
	Isometric supination	Overall	6.0 ± 4.1	11.5 ± 6.2	5.5 (47.8)	< 0.001
		Males	8.6 ± 5.0	15.1 ± 6.6	6.5 (43.0)	0.004
		Females	4.5 ± 2.7	8.7 ± 4.2	4.2 (48.3)	< 0.001
	Isometric pronation	Overall	8.0 ± 5.6	12.8 ± 6.4	4.8 (37.5)	< 0.001
		Males	10.8 ± 6.1	16.7 ± 6.3	5.9 (35.3)	0.008
		Females	6.5 ±4.8	9.7 ± 4.6	3.2 (33.0)	0.002
Non-dominant hand	Static grip	Overall	8.5 ± 6.7	13.0 ± 6.8	4.5 (34.6)	< 0.001
		Males	12.3 ± 7.9	17.3 ± 7.0	5.0 (28.9)	0.029
		Females	6.4 ± 5.0	9.6 ± 4.3	3.2 (33.3)	0.002
	Isometric supination	Overall	5.4 ± 4.1	10.1 ± 5.0	4.7 (46.5)	< 0.001
		Males	6.4 ± 3.5	13.1 ± 5.0	6.7 (51.1)	< 0.001
		Females	4.9 ± 3.6	7.7 ± 3.5	2.8 (36.4)	0.001
	Isometric pronation	Overall	6.7 ± 4.8	11.6 ± 5.8	4.9 (42.2)	< 0.001
		Males	7.9 ± 4.4	15.4 ± 5.7	7.5 (48.7)	< 0.001
		Females	5.9 ± 4.9	8.6 ± 3.9	2.7 (31.4)	0.003

Maximum functional isometric grip strengths

The maximum isometric grip strengths in all three measurements for fallers are presented in Figures 2 and 3. Decrease in grip strength was observed when isometric forearm torque was simultaneously applied. Compared to static grip strength (dominant hand), isometric supination grip strength decreased by 31.2% (median: 15.4 kg vs 10.6 kg; p = 0.004; Z = -2.845) and 16.7% (median: 7.2 kg vs 6.0 kg; p = 0.005; Z = -2.837) for male and female fallers, respectively. In contrast, the dominant hand grip strength during isometric pronation decreased by 30.5% (median: 15.4 kg vs 10.7 kg; p = 0.021; Z = -2.312) and 6.9% (7.2 kg vs 6.7 kg; p = 0.117; Z = -1.568) for male and female fallers, respectively.

Figure 2.

The box plot represents the distribution of the functional isometric grip strengths (male fallers). The middle line represents the median, the red-filled circle represents the mean and the whiskers represent the range of data.

Figure 3.

The box plot represents the distribution of the functional isometric grip strengths (female fallers). The middle line represents the median, the red-filled circle represents the mean and the whiskers represent the range of data.

Maximum vs sustained functional isometric grip strength

The average 10 seconds of sustained isometric grip strengths were calculated and compared to the maximum isometric grip strengths. The highest difference was found in isometric supination, in which the dominant hand sustained grip strength decreased by 19.8% (median: 10.6 kg vs 8.5 kg; p = 0.003; Z = -2.934) and 26.7% (median: 6.0 kg vs 4.4 kg; p < 0.001; Z = -3.92) for male and female fallers, respectively. In contrast, the difference between the maximum and sustained isometric pronation strengths was 1.9% (median: 10.7 kg vs 10.5 kg; p = 0.003; Z = -2.934) and 23.9% (median: 6.7 kg vs 5.1 kg; p < 0.001; Z = -3.92) for male and female fallers, respectively.

Discussion

Grip strength is known to represent the overall muscle strength and functional capacity of an individual, and has been used as an important clinical tool to assess early symptoms of frailty in ageing individuals.^8–13 Additionally, normative reference values for specific populations, such as those in Singapore, South Korea, Canada and Europe, have been established,^{15, 24–27} and cutoff grip strength values to screen elderly people at risk have also been implemented.^28–29 For example, the Asian Working Group for Sarcopenia²⁹ suggested that grip strength below 26 kg for males or 18 kg for females would signify a higher risk of sarcopenia. However, although maximum static grip strength has always been recognized as a standard clinical measure, the literature has suggested that dynamic or functional isometric grip strengths might better represent the individual’s grasping capabilities due to the simultaneous action of gripping and forearm torque.^{13–15, 30} In this study, the elderly fallers recruited were clinically assessed as either pre-frail (no or low frailty based on the Modified Frailty Index score) or frail, and most of them have at least mild cognitive impairment and are functionally dependent. It is important to note that there were no statistical differences between fallers regardless of their frailty index score.

Our results have quantified the changes in grip strength while applying isometric forearm torque force in pronation and supination directions. One of the important observations made was that grip strength is at its weakest during isometric supination. This means if a particular task requires an elderly faller to apply his/her maximum grip while simultaneously exerting isometric forearm torque in the supination direction, for example, when wringing out clothes, they are only capable of achieving up to 68% (male) or 83% (female) of their maximum static grip strength. The healthy community-dwelling elderly people in our previous normative study¹⁵ were also able to achieve about 80% of their maximum static grip strength while concurrently applying isometric forearm supination. Isometric pronation, however, reduces the grip strength by much less.

Additionally, we have investigated the average sustained functional grip strengths in order to further our understanding of the grip profile of elderly fallers. Sustained grip strength refers to the ability to maintain maximum isometric grip strength for a period of time,^30–35 which in this case is 10 seconds. Studies have suggested that measuring sustained grip strength could provide useful information on overall hand function,^30–34 particularly with regard to assessing elderly fallers’ ability to repeat a physical task or grasp an object intensively over a period of time, for example, opening a bottle/jar with a tightly fitting lid, mopping the floor or putting laundry poles out. The latter is a typical practice in Singapore, but an unsafe task for an elderly person who has low sustained grip strength.

In a study by Bautmans et al.,³⁴ the authors have suggested that grip work is a promising outcome measure to be used in geriatric assessment. Grip work is calculated based on both maximal grip strength and the duration the individual can maintained before the strength decrease to a critical threshold (i.e. 50% of the maximal strength). Based on the results obtained from community-dwelling elderly and geriatric patients, the authors found that grip work was significantly related to physical functioning, mobility and self-perceived fatigue, and thus proposed that this would be a reliable method to monitor changes in muscle endurance and/or fatigue in elderly people. Similarly, in another study by Dobbeleer et al.,³⁵ the authors have conducted a series of studies investigating muscle endurance in geriatric patients based on grip work, and have reported that geriatric patients displayed rapid decline in grip strength during the first 10 seconds of their sustained strength, and their grip work was significantly lower than the physically independent elderly. Although grip work was not calculated in this study, our results have shown similar grip strength characteristic, whereby the sustained grip strength was found to be lower than maximum grip strength. In the faller group, it was observed that the elderly could not maintain the maximum grip strength within the given time as their average sustained grip results have been shown to decrease, with the lowest sustained strength measured at 8.5 kg (male) or 4.4 kg (female) during isometric supination, which translates to 20% (male) and 27% (female) weaker than the maximum isometric supination grip. In contrast, our previous study on community-dwelling elderly people reported that the sustained grip strength during isometric supination was 17% (male) and 24% (female) lower than the maximum isometric supination grip strength.

The main limitation of our study is the small sample size, because about 40% of the elderly fallers recruited were unable to comply with or complete the functional grip strength assessments. Nevertheless, our results clearly show that elderly fallers are weaker, especially when their grip is subject to additional torque, endurance or both. The findings have potential implications for designing better screening tools for the geriatric population, which may contribute to identifying elderly people who are at a higher risk of falling.

Footnotes

Acknowledgements

We would like to thank the clinical research coordinator, Ms. Natasha Tian Adam, for her assistance in this research.

Authors’ contributions

THW and ISMJ contributed to the study design, data collection, data interpretation and the drafting of this manuscript. ISMJ and NVN performed statistical analyses. All of the authors have made substantive intellectual contributions to the study. All authors have read and approved the final version of the manuscript.

Ethical approval

Ethical approval to report this case was obtained from the SingHealth Centralized Institutional Review Board (Ref: 2016/2004).

Informed consent

Written informed consent was obtained from all subjects before the study.

Availability of data

The datasets generated and/or analysed during the current study are available from the corresponding author.

Trial registration

Not applicable because this is not a clinical trial study.

Declaration of conflicting interest

The authors declare that there is no conflict of interest.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This research was supported by the Mitsui-Sumitomo Insurance Welfare Foundation Research Grant 2015 and the Singapore Ministry of Health’s National Medical Research Council under its Centre Grant (NMRC/CG/M011/2017).

ORCID iD

Ita Suzana Mat Jais

References

Prata

Scheicher

ME.

Relationship between fear of falling and quality of life in older women fallers. MOJ Gerontol Geriat. 2017; 1: 128–131.

Dionyssiotis

Analyzing the problem of falls among older people. Int J Gen Med. 2012; 5: 805.

Sharif

Al-Harbi

Al-Shihabi

et al. Falls in the elderly: assessment of prevalence and risk factors. Pharm Pract. 2018; 16: 1206.

Vieira

Palmer

Chaves

PH.

Prevention of falls in older people living in the community. BMJ. 2016; 353: i1419.

Merchant

Chen

Tan

et al. Singapore Healthy Older People Everyday (HOPE) Study: prevalence of frailty and associated factors in older adults. J Am Med Dir Assoc. 2017; 18: 734-e9.

Vaingankar

Chong

Abdin

et al. Prevalence of frailty and its association with sociodemographic and clinical characteristics, and resource utilization in a population of Singaporean older adults. Geriatr Gerontol Int. 2017; 17: 1444–1454.

Wong

Nguyen

Chiu

et al. The low fall as a surrogate marker of frailty predicts long-term mortality in older trauma patients. PLoS ONE. 2015; 10: e0137127.

Lenardt

Binotto

Carneiro

et al. Handgrip strength and physical activity in frail elderly. Rev Esc Enferm USP. 2016; 50: 86–92.

Syddall

Cooper

Martin

et al. Is grip strength a useful single marker of frailty? Age Ageing. 2014; 32: 650–656.

10.

Shechtman

Mann

Justiss

et al. Grip strength in the frail elderly. Am J Phys Med Rehabil. 2004; 83: 819–826.

11.

Taekema

Gussekloo

Maier

et al. Handgrip strength as a predictor of functional, psychological and social health. A prospective population-based study among the oldest old. Age Ageing. 2010; 39: 331–337.

12.

Bohannon

RW.

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

13.

LaStayo

Hartzel

Dynamic versus static grip strength: how grip strength changes when the wrist is moved, and why dynamic grip strength may be a more functional measurement. J Hand Ther. 1999; 12: 212–218.

14.

Richards

Olson

Palmiter-Thomas

How forearm position affects grip strength. Am J Occup Ther. 1996; 50: 133–138.

15.

Mat Jais

Chan

Loke

et al. Normative data on functional grip strength of elderly in Singapore. J Hand Ther. 2018; 31: 122–128.

16.

Katz

Downs

Cash

et al. Progress in development of the index of ADL. Gerontologist. 1970; 10: 20–30.

17.

Shelkey

Wallace

Katz index of independence in activities of daily living (ADL). Int J Older People Nurs. 2012; 2: 204–212.

18.

Shah

Vanclay

Cooper

Improving the sensitivity of the Barthel Index for stroke rehabilitation. J Clin Epidemiol. 1989; 42: 703–709.

19.

Beaton

Wright

Katz

et al. Development of the QuickDASH: comparison of three item-reduction approaches. J Bone Joint Surg Am. 2005; 87: 1038–1046.

20.

Chiam

Kua

EH.

Ethnic and educational differences in cognitive test performance on mini-mental state performance in Asians. Am J Geriatr Psychiatry. 2007; 15: 130–139.

21.

Farhat

Velanovich

Falvo

et al. Are the frail destined to fail? Frailty index as predictor of surgical morbidity and mortality in the elderly. J Trauma Acute Care Surg. 2012; 72: 1526–1531.

22.

Mathiowetz

Weber

Volland

et al. Reliability and validity of grip and pinch strength evaluations. J Hand Surg Am. 1984; 9: 222–226.

23.

Fess

EE.

Grip strength. In: Casanova

(ed.) Clinical assessment recommendations. 2nd ed. Chicago, IL: The American Society of Hand Therapists, 1992, pp.41–45.

24.

Malhotra

Ang

Allen

et al. Normative values of hand grip strength for elderly Singaporeans aged 60 to 89 years: a cross-sectional study. J Am Med Dir Assoc. 2016; 17: 864.e1–7.

25.

Shim

Roh

Kim

et al. Normative measurements of grip and pinch strengths of 21st century Korean population. Arch Plast Surg. 2013; 40: 52–56.

26.

Desrosiers

Bravo

Hebert

et al. Normative data for grip strength of elderly men and women. Am J Occup Ther. 1995; 49: 637–644.

27.

Günther

Bürger

Rickert

et al. Grip strength in healthy Caucasian adults: reference values. J Hand Surg Am. 2008; 33: 558–565

28.

Sallinen

Stenholm

Rantanen

et al. Hand-grip strength cut points to screen older persons at risk for mobility limitation. J Am Geriatr Soc. 2010; 58: 1721–1726.

29.

Chen

Liu

Woo

et al. Sarcopenia in Asia: consensus report of the Asian Working Group for Sarcopenia. J Am Med Dir Assoc. 2014; 15: 95–101.

30.

Jung

Hallbeck

MS.

The effect of wrist position, angular velocity, and exertion direction on simultaneous maximal grip force and wrist torque under the isokinetic conditions. Int J Ind Ergon. 2002; 29: 133–143.

31.

Desrosiers

Bravo

Hébert

Isometric grip endurance of healthy elderly men and women. Arch Gerontol Geriatr. 1997; 24: 75–85.

32.

Kamimura

Ikuta

Evaluation of grip strength with a sustained maximal isometric contraction for 6 and 10 seconds. J Rehabil Med. 2001; 33: 225–229.

33.

Lagerström

Nordgren

Methods for measuring maximal isometric grip strength during short and sustained contractions, including intra-rater reliability. Ups J Med Sci. 1996; 101: 273–285.

34.

Bautmans

Onyema

Van Puyvelde

et al. Grip work estimation during sustained maximal contraction: validity and relationship with dependency and inflammation in elderly persons. J Nutr Health Aging. 2011; 15: 731–736.

35.

De Dobbeleer

Beyer

Njemini

et al. Force-time characteristics during sustained maximal handgrip effort according to age and clinical condition. Exp Gerontol. 2017; 98: 192–198.

Investigating the functional grip strength of elderly fallers in Singapore