Maximum handgrip strength as a function of type of work and hand-forearm dimensions

Abstract

BACKGROUND:

Handgrip strength is a measurement of upper extremity functionality and an indicator of overall physical ability.

OBJECTIVES:

The objective of this study was to compare maximum handgrip strength (MGS) between manual workers and office employees and to investigate if the expected difference is related to the anthropometric dimensions of the workers’ hands and forearms.

METHODS:

This was a cross-sectional study with a sample of 1740 male workers (905 light manual workers; and 835 office employees), aged 20–64 years. Maximum voluntary contractions were obtained using a JAMAR dynamometer according to the methodology proposed by the American Society of Hand Therapy (ASHT). The highest value obtained from three trials was considered as the MGS for each side. Six anthropometric dimensions (i.e., hand length, palm length, forearm length, hand breadth, wrist circumference and forearm circumference) were measured by digital caliper and tape measure.

RESULTS:

Maximum handgrip strength of light manual workers (52.7±8.5 kg) was significantly higher than that of office employees (47.3±8.4 kg) (p < 0.001). Maximum handgrip strength was positively correlated with Hand breadth (r = 0.781 for light manual workers and r = 0.766 for office employees; p < 0.001) and Forearm circumference (r = 0.741 for light manual workers and r = 0.752 for office employees; p < 0.001); the only dimensions which were significantly different between the two studied job groups.

CONCLUSIONS:

The results of this study revealed that light manual workers are approximately 12.4% stronger than office employees in terms of maximum handgrip force. It is therefore imperative to consider the observed differences in clinical, workstations, and hand tool designs in order to increase efficiency and comfort at work.

Keywords

Anthropometric factors dynamometer occupational group workers

1 Introduction

Hands are comprised of a complex array of nerves, tendons, muscles and bones that enable us to move our fingers in ways that machines cannot match. In many workplaces, hands are frequently used for such actions as manual lifting, pushing, pulling, grasping, carrying, etc. During these activities, workers’ hands are primarily used for applying force on the equipment/tools’ handles. There are 35 muscles involved in the movement of the forearm and hand, with many of them involved in gripping activities [1]. The complex muscular system of the hand is composed of two types of muscles: extrinsic and intrinsic. Originating in the forearm, extrinsic muscles are large and long muscles compared to the intrinsic muscles generating powerful contractions. Hand muscles are entirely composed of short and small muscles (intrinsic muscles) providing weak but precise finger movements [2]. However, intrinsic muscles of the hand depend also on forearm muscles for their functionality. During gripping activities, the flexor muscles of the hand and forearm create grip strength, while the extensors of the forearm stabilize the wrist. Together, the hand, wrist, and forearm form an interdependent system for the performance of manual tasks [1, 3].

Grip strength, also known as hand strength, is an anthropometric measurement that indicates muscle health in the hands and forearms [4]. It is an important index of overall physical strength and a main biomarker of aging, general health, and nutritional status [5, 6]. It could indicate full body strength, overall function [7], neuromuscular activation [8], and work capacity [9]. It is well-known that grip strength in later life is independently associated with chronic diseases [10], disability, morbidity, and cancer [11]. For instance, a recent study reported that an 11-pound decrease in grip strength was correlated with a 17 percent increased risk of cardiovascular death, a 7 percent increased risk of heart attack, and a 9 percent increased risk of stroke [12].

Hand strength is usually determined by the maximum voluntary force that an individual is able to exert under normal biokinetic conditions [13]. Stronger upper extremity muscle strength is positively related to the quality and value of handgrip strength. In workplaces, poor handgrip strength can lead to a host of problems such as fatigue due to overexertion of the hands (a major cause of reduced working performance), musculoskeletal injuries caused by repeated hand overexertion, objects being more frequently dropped from or slipped through the hands (a potential danger for other parts of the body or co-workers), transferring muscle exertion from the hand to other parts of the body to compensate, increased risk of cuts, lack of hand hygiene, dermatological risks to the skin, loss of control over work, and loss of productivity due to slowing down to compensate for a poor grip [14, 15].

Moreover, it has been shown that handgrip strength is affected by various factors such as age, height, gender, hand dominance, body mass index (BMI), skeletal size, chronic disease, occupation, and ethnicity [16, 17]. Previous studies have found that handgrip strength has a nonlinear relationship with age. The peak of handgrip strength is usually seen in the 4th decade of life and then it declines gradually [18]. Research supports that handgrip strength increases linearly with height, weight, and BMI [19, 20] and is often greater in the dominant hand [21]. Some hand anthropometric dimensions, such as hand length, palm length, palm width, and hand circumference, are also known to be positively related with grip strength, hand performance and worker productivity [22]. In general, handgrip strength and grasping ability increase with hand size [23 –25].

Some recently conducted studies reported that higher handgrip strength is related to higher work ability (i.e., the ability to perform a job with respect to the specific work demands), especially in workers who are engaged in manual tasks and exert forceful activities with their upper extremities in the workplace [26 –28]. Regarding that, for safe and usable hand tool design, it is necessary to pay more attention to workers’ capabilities/limitations in comparison to the requirements of work tasks. The reason for this is that workforce capacity to perform mechanical and manual work is determined by the workers’ abilities to exert muscular strength and grasp [29, 30]. For instance, workers engaged in relatively heavy manual works are found to have greater handgrip force compared to office workers. However, to our knowledge, no study has focused on handgrip ability of light manual workers whose duties are though manual but to a lesser extent than heavy manual workers. The present study provides a large sample of normative data for clinical use in hand and upper limb rehabilitation and possible screening for other health issues. It also explores the relationship of grip strength with demographic characteristics and some hand dimensions. The key objectives of the study reported here are to quantify: (1) any differences in the maximum handgrip strength and hand anthropometric dimensions between light manual workers and office employees, (2) important contributors to handgrip strength among studied demographic factors as well as hand and forearm dimensions.

2 Material and methods

2.1 Participants

This study had a cross-sectional design and included 1740 healthy adult males (905 light manual workers and 835 office employees), aged 20–64 years. Participants were selected using a stratified random sampling method from a public university in Iran. Participants were classified into two job groups according to their occupational title. Consequently, those workers who had similar duties and skills were grouped together. The first group was composed of unskilled workers who performed light manual tasks which generally require no special training to perform in routine daily work activities. These tasks included sweeping and cleaning office rooms, housekeeping, gardening, driving and restoration. The second group was composed of office employees who were engaged in all types of clerical or administrative work that helped to support and realize the objectives and goals of the organizations. Job titles associated with this group included bookkeepers, office machine operators (including computer), typists, secretaries, etc. Inclusion criteria were as follows: absence of cardiac, pulmonary, metabolic or neurological diseases; absence of surgery or fracture history in the hands, neck and upper extremities in the past 6 months; and lack of pain in the upper extremities at the time of evaluation. The study was approved by the local research ethics committee and an informed consent was signed by all participants.

2.2 Measurements procedures

Measurements were carried out in a separate room in the workplace. Two measurers collected data during working hours. The Technical Error of Measurement (TEM) was used as an evaluation index to the accreditation of the measurers [31]. Considering the reliability of the measurements, Mathiowetz et al. (1984), demonstrated high inter-rater and test-retest reliability by using the JAMAR hand dynamometer and following the standardized positioning and instructions recommended by the American Society of Hand Therapists (ASHT) [32].

The age of participants was recorded from their personal identification cards. Stature and body mass were measured to the nearest 0.1 cm and 0.1 kg using a ProScale M10 digital stadiometer and an electronic scale, respectively. Body mass index was calculated in kg/m².

2.2.1 Hand anthropometric measurements

As shown in Fig. 1, the following hand dimensions were taken on both sides of each participant using a digital caliper (±0.1 mm) and a tape measure (±0.1 cm), according to the standardized procedure [33]. Hand Length (HL) was defined as the distance between the stylion landmark on the wrist and the tip of the middle finger (dactylion III). Palm Length (PL) was defined as the distance between the stylion landmark on the wrist and the crease at the base of the middle finger. Hand Breadth (HB) was considered as the distance between the landmarks at metacarpals II and V. Wrist Circumference (WC) was defined as the circumference of the wrist, measured slightly proximal to the styloid process of radius. Forearm Length (FL) was defined as the horizontal distance between points radiale and stylion. Forearm Circumference (FC) was defined as the circumference of the forearm at the point of maximum prominence, slightly distal to the elbow joint.

Fig. 1

Position of the hand-arm of participants during evaluation and anthropometric measurements. A: hand length (solid line), palm length (long dash line), and hand breadth (square dot line); B: forearm length, wrist circumference, forearm circumference.

The hand and forearm measurements were taken with the segments held flat in a supinated position, with palm and elbow on a table, fingers together, and the thumb abducted. Each hand dimension was measured twice and the average was calculated and recorded for analysis. Calibration of all equipment was conducted prior to and during the data collection period.

2.2.2 Maximum handgrip strength (MGS)

Maximum voluntary handgrip strength was measured in kilograms for both hands using a standard adjustable JAMAR hydraulic dynamometer (Hersteller/manufactures; SEHAN Corporation, Masan-Korea; Distributer Rehaforum Medical GmbH, Elmshorn-Germany). The handle was set at the second position for all tests, because it is recommended as the standard for Jamar handle positioning [34]. Before starting the test, hand dominance was determined by asking participants the following question: “Which hand do you write with?” Participants were then seated appropriately and testing was carried out in accordance with the standard positioning and instructions recommended by ASHT [35]. Accordingly, participants were instructed to sit on a chair without armrests with the shoulder adducted and neutrally rotated, the elbow flexed at 90°, forearm and wrist in neutral position (0–15 degrees of extension and ulnar deviation). They were asked to squeeze the dynamometer at maximal effort for three trials, with a 1-minute break between each trial. An initial demonstration was presented by the tester as well as the appropriate Persian translation of the verbal instructions for grip strength and verbal encouragement (harder ... harder!) to ensure maximal effort during each measurement. The maximum handgrip strength of the three trials was recorded for each hand.

2.3 Statistical analysis

SPSS 23 (IBM Corporation, New York, NY, United States) was used for statistical analysis. Normality was evaluated using the one-sample Kolmogorov-Smirnov (K-S) test. The mean and standard deviation (SD) of maximum HGS and selected hand dimensions, and 95% confidence intervals (CIs) were calculated for each 5-year interval starting from 20 years of age. Man-Whitney and student’s t-test were used to compare the subjects’ characteristics between light manual workers and office employees. Paired sample t-test was used to compare MGS for the dominant hand and non-dominant hand. One-way ANOVA test was used to compare MGS of dominant and non-dominant hand, allocated according to age- and job-group. According to the results of the Levene’s test, indicating equal or unequal variances, Scheffe or Games-Howell post-hoc tests were used, respectively. Pearson’s correlation coefficients were used to determine the correlations among the selected hand anthropometric and demographic variables and maximum HGS of both hands. Statistical significance was considered at an alpha level of 0.05.

3 Results

Descriptive statistics of participant characteristics are presented in Table 1. Ninety-one percent of participants were right-handed, while none were ambidextrous.

Table 1
Mean±SD and range of participant characteristics as a function of occupation

Variable Light Manual Workers (n = 905) Office Employees (n = 835)

Mean±SD Min-Max Mean±SD Min-Max

Age (years) 40.5±16.8 21.3 –62.7 48.3±18.2 20.6 –64.2

Body mass (kg) 71.3±9.3 64.1 –96.5 78.1±4.3 63.4 –102.6

Height (cm) 173.2±7.1 158.2 –193.1 171.9±3.1 166.7 –201.6

BMI (kg/m²) 23.2±2.8 18.6 –31.7 25.8±4.0 19.3 –36.2

Variable	Light Manual Workers (n = 905)	Office Employees (n = 835)
Age (years)	40.5±16.8	21.3 –62.7	48.3±18.2	20.6 –64.2
Body mass (kg)	71.3±9.3	64.1 –96.5	78.1±4.3	63.4 –102.6
Height (cm)	173.2±7.1	158.2 –193.1	171.9±3.1	166.7 –201.6
BMI (kg/m²)	23.2±2.8	18.6 –31.7	25.8±4.0	19.3 –36.2

Table 2 represents maximum handgrip strength according to hand dominancy as well as age and job groups. Maximum handgrip strength of light manual workers was significantly higher than that of office employees for the dominant hand (52.7±8.5 kg vs. 46.1±8.0 kg) and non-dominant hand (47.3±8.4 kg vs. 41.8±7.9 kg). The difference between the worker groups fluctuated from 4% to 12.5% for the dominant hand and from 6% to 11.6% for the non-dominant hand. Moreover, the dominant hand was stronger on average than the non-dominant hand in both job groups (10.2% for light manual workers and 9.3% for office employees).

Table 2

Mean±SD maximum handgrip strength (MGS) (kg) for both hands of light manual workers (n = 905) and office employees (n = 835) by age group

Age group (years)	n_m	n_o	Maximum Handgrip Strength (kg)
			Dominant hand			Non-Dominant hand
			Light Manual Workers	Office Employees	D	Light Manual Workers	Office Employees	D
20–24	98	89	52.3±7.6	46.1±6.3	6.2	46.3±6.8	40.3±5.1	6.1
25–29	101	85	53.4±7.0	46.8±6.7	6.6	47.8±7.5	42.9±7.2	4.9
30–34	108	83	55.1±8.3	48.2±8.6	6.9	49.6±7.8	44.3±9.7	5.3
35–39	97	92	59.0±9.0	51.9±8.0	7.1	52.5±8.8	48.5±7.3	4.0
40–44	99	103	57.1±8.8	50.0±7.2	7.1	50.2±9.7	45.2±6.8	5.0
45–49	105	96	53.9±8.7	47.8±8.6	6.1	48.8±9.0	42.3±8.2	6.5
50–54	97	97	51.7±9.7	44.1±9.5	7.6	48.0±8.1	40.2±8.7	7.8
55–59	97	97	48.0±8.0	42.4±8.2	5.6	43.2±7.3	37.3±7.9	5.9
60–64	103	93	43.7±8.9	37.3±8.7	6.4	39.2±7.6	34.1±8.1	5.1
Total	905	835	52.7±8.5	46.1±8.0	6.6	47.3±8.4	41.8±7.9	5.5

D: MGS _{Light manual worker} –MGS _{Office employees .} n_m: Number of light manual workers, n_o: Number of office employees.

The age group of 35–39 years had a higher maximum handgrip strength in comparison to the other age groups, whatever the occupation type. As seen in Table 2, the maximum handgrip strength increased up to the 35–39 year age range and then decreased gradually (in both light manual workers and office employees, as well as on the dominant and non-dominant sides).

Descriptive statistics of hand and forearm dimensions by hand side and occupational group are shown in Table 3. Hand breadth and forearm circumference were significantly different between the two occupational groups (p < 0.001). Light manual workers had greater hand breadth and forearm circumference than office employees, in both upper extremities. Other hand dimensions were not statistically different between the two groups (p > 0.05).

Table 3

Mean±SD hand anthropometric dimensions (cm) for both hands of light manual workers and office employees

Variable	Light Manual Workers	Office Employees	p-value
Dominant hand
Hand length (cm)	20.05±0.90	19.25±0.5	0.450
Palm length (cm)	11.65±0.63	10.80±0.1	0.383
Hand breadth (cm)	11.82±0.26	9.92±0.40	<0.001
Forearm length (cm)	27.45±1.15	27.00±0.8	0.300
Wrist circumference (cm)	19.65±1.00	18.83±0.0	0.345
Forearm circumference (cm)	29.35±2.27	26.53±0.4	<0.001
Non-dominant hand
Hand length (cm)	19.70±0.85	19.00±0.89	0.301
Palm length (cm)	11.45±0.56	11.00±0.61	0.287
Hand breadth (cm)	11.00±0.41	9.30±0.48	<0.001
Forearm length (cm)	26.91±1.25	26.12±1.10	0.245
Wrist circumference (cm)	19.83±0.98	19.00±0.79	0.269
Forearm circumference (cm)	29.25±2.03	26.95±2.03	<0.001

p-value_(Bold) = Significant at 0.05 level.

All demographic and anthropometric variables were significantly correlated with maximum handgrip strength (Table 4). Due to the curvilinear relationship between the MGS and age, two trends were observed in their changes. The MGS increased up to the 35–39 year age range and decreased gradually thereafter, in both occupational groups. MGS fluctuations across the age groups for both dominant and non-dominant hands are illustrated in Fig. 2. Pearson’s correlation coefficients among MGS and age group were analyzed (Table 4). In general, higher correlation coefficients (0.583–0.636; p < 0.001) between the MGS of light manual workers and age were reflected by a substantial increment of MGS within the age range of 20–39 years. However, correlations demonstrating the dependence of the MGS of the office employees to their age (–0.440 to –0.511; p < 0.001) were generally higher than the light manual workers after 40’s. In addition, body mass, height, and BMI of participants were highly correlated with maximum handgrip strength. Among hand dimensions, hand breadth had the highest correlation with handgrip strength (r = 0.781 and r = 0.755, p < 0.001 for the dominant and non-dominant hands of light manual workers, respectively; r = 0.766 and r = 0.740, p < 0.001 for the dominant and non-dominant hands of office employees, respectively), followed by forearm circumference (r = 0.741 and r = 0.740, p < 0.001 for dominant and non-dominant hands of light manual workers, respectively; r = 0.752 and r = 0.722, p < 0.01 for dominant and non-dominant hands of office employees, respectively).

Table 4

Pearson’s correlation coefficients between the maximum handgrip strength of each hand with demographic and anthropometric variables

Variables	Light Manual Workers (n = 905)			Office Employees (n = 835)
	MGS_D	MGS_ND	p-values	MGS_D	MGS_ND	p-values
Age
20–64 years	–0.080	–0.110	>0.05	–0.108	–0.100	>0.05
20–39 years	0.636	0.583	<0.001^*	0.528	0.517	<0.001^*
40–64 years	–0.337	–0.331	<0.001^*	–0.511	–0.440	<0.001^*
Body Mass	0.583	0.570	<0.001^*	0.549	0.550	<0.001^*
Height	0.642	0.635	<0.001^*	0.621	0.630	<0.001^*
BMI	0.378	0.390	<0.001^*	0.377	0.352	<0.001^*
HL_D	0.693	–	<0.001^*	0.703	–	<0.001^*
HL_ND	–	0.673	<0.001^*	–	0.619	<0.001^*
HB_D	0.781	–	<0.001^*	0.766	–	<0.001^*
HB_ND	–	0.755	<0.001^*	–	0.740	<0.001^*
PL_D	0.664	–	<0.001^*	0.645	–	<0.001^*
PL_ND	–	0.669	<0.001^*	–	0.655	<0.001^*
WC_D	0.305	–	0.004^*	0.312	–	0.005^*
WC_ND	–	0.295	0.006^*	–	0.305	0.007^*
FC_D	0.741	–	<0.001^*	0.752	–	<0.001^*
FC_ND	–	0.740	<0.001^*	–	0.722	<0.001^*
FL_D	0.577	–	<0.001^*	0.566	–	<0.001^*
FL_ND	–	0.559	<0.001^*	–	0.590	<0.001^*

^*p < 0.05. MGS (kg): Maximum handgrip strength; D: dominant hand; ND: non-dominant hand; BMI: body mass index; HL (cm): hand length; HB (cm): hand breadth; PL (cm): palm length; WC (cm): wrist circumference; FC (cm): forearm circumference; FL (cm): forearm length.

Fig. 2

MGS performance by age groups and hand dominance for light manual workers and office employees.

4 Discussion

This study was conducted to identify the normal values of maximum handgrip strength in light manual workers and office employees, to create a reference scale of selected hand anthropometric dimensions in studied occupational groups, and also to determine the most effective contributors to MGS.

The maximum handgrip strength results showed significant differences between the two studied occupational groups; light manual workers being on average 12% stronger than their office co-workers in terms of handgrip strength. It may be that some anthropometric dimensions are greater in manual workers compared to non-manual workers [36]. It is believed that this is the result of strong and repetitive movements which increase muscle strength, muscle mass, and ultimately handgrip strength and arm strength in manual workers [27 , 38]. Nevertheless, in the present study, the mean age of manual workers was lower than for the other group. Therefore, the observed higher MGS in manual workers may partly be a reflection of their younger age. This needs to be investigated in future studies.

In both occupational groups, the maximum handgrip strength decreased significantly as age increased. This may be caused by a reduction in muscle mass with age [39]. Regarding this issue, Abe et al. (2016) revealed that the thickness of the anterior forearm muscles (at 30% proximal between the styloid process of the ulna and the head of the radius) decreases with aging, leading to decrements in HGS [40]. This effect is more substantial after the age of 70 years due to the increased muscle loss in this age range [41, 42]. Seemingly, the development and maintenance of muscle mass in adulthood reduces the risk of developing sarcopenia for aging workers who are engaged in manual activities. Several studies suggest that the HGS-age relationship is curvilinear, with the peak usually occurring within the 35 to 50 years age range. The results from this study are in agreement with previous findings [43, 44].

Research suggests that the handgrip strength of the dominant hand is 10% greater than the non-dominant hand [36]. The results of the present study showed that this is also the case for maximum handgrip strength.

Handgrip strength is positively related to hand size. Our findings are in good agreement with previous studies in which a strongly positive correlation was found between handgrip strength and hand size [28 , 45]. It is apparent that some anthropometric dimensions could be more determinative than others since hand breadth and forearm circumference were more strongly correlated with MGS. Fat-free cross sectional area has been found to be positively correlated with handgrip strength. Indeed, grip force producing muscles are predominantly located in the forearm but would be more affected by body fat compared to hand breath [46]. The difference between the percentage of muscularity/fatness has been suggested to be responsible for different HGS between various occupational groups (brick-field workers vs. sedentary workers) [47] or between peoples with different national origins (Middle-Eastern vs. Asian and African [48]. This could also explain our findings in which the mean BMI of the manual-workers group was normal, and on average, 2.6 kg less than the other group (overweight). Regular labour, like mild to vigorous training, can prevent the accumulation of fat in the body [47].

There were some strengths and limitations of this study. First, the findings of this study fail to establish a true cause and effect relationship because the study was cross-sectional in design. Second, although the studied population was one of the largest for determining maximum handgrip strength, other occupational groups such as heavy manual, automotive workers, etc., were not evaluated. Finally, being beyond the scope of this study, some other factors like nutritional status, sports participation, and ethnicity may affect handgrip strength. Further studies is needed to elaborate this topic. However, this study was meaningful because it analyzed the differences in MGS according to age and occupational groups.

5 Conclusions

In conclusion, normative values of maximum handgrip strength were presented and differences in selected hand dimensions for light manual workers and office employees were examined. These reference values are essential for the design of hand tools, workstations, and worker selection techniques, according to their capabilities and limitations. More specifically, when designing hand tools, factors that affect HGS, such as cross-occupational similarities and differences and age, should be taken into account by designers. The findings also can be used by occupational therapists and health professionals to compare them with the handgrip strength values of their patients to make accurate diagnoses and treatment protocols.

Conflict of interest

None to report.

Footnotes

Acknowledgments

This study was supported financially by research deputy of Shahid Beheshti University of Medical Sciences, Tehran, Iran. The authors would like to express special thanks to all the participants for giving up their time for this research.

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