Wrist ulnar/radial torque strength measurements among Iranian population: The effects of age,gender,Body Mass Index and hand dominance

Abstract

BACKGROUND:

Data on the physical strength capabilities of users are essential for designing the safe and usable products.

OBJECTIVE:

The aims of this study were to characterise the wrist ulnar/radial (U/R) torque strength and individual strength differences among Iranian population.

METHODS:

The study was conducted among 769 (391 males, 378 females) participants aged 5–74 years in the northwest of Iran. Measurements were carried out with both dominant and non-dominant hands using a digital angle torque adaptor installed in a jar-shaped measuring unit.

RESULTS:

The results indicated that the mean wrist U/R torque strength exertion by females was 75% of that exerted by males. Strength exertion with the non-dominant hand was 8% lower than strength exertion of the dominant hand. A significant positive association was also found between the wrist U/R torque strength and body mass index.

CONCLUSIONS:

This additional information on the wrist torque strength can fill the gap in the strength data for Iranian population, or used by health and safety practitioners in the field.

Keywords

Force hand muscular exertion individual differences

1 Introduction

The human hand is one of the most sophisticated and complex anatomical structures in the body, which is capable of doing extremely fine and sensitive movements and exerting considerable force. To perform such sophisticated functions, the human hand has been equipped with both mechanical and sensory capabilities [1].

The nature of many tasks and working situations involves the use of muscular strength. The need for muscular strength to perform physical activities remains strong despite increasing automation [2]. Manual material handling activities, transferring patients to and from their beds, performing maintenance activities and many other manual industrial tasks may regularly require repetitive of forceful muscular exertions. Many daily and occupational activities require the muscular strength in the form of hand grip strength, pinch strength or torque strength [2]. The human hand torque strength, based on wrist postures, can be classified as pronation/supination (P/S), extension/flexion (E/F) and radial/ulnar (U/R) deviation torque strength [3]. The most common examples of radial/ulnar torque tasks are using the wrist to open vacuum-sealed jars or to open or close a hand-wheel value.

Muscular strength measurements are performed for various purposes. Hand strength measurement is used in a wide range of clinical settings, particularly during treatment of disease affecting the function of the hand [4]. The data on the physical strength capabilities of users are also essential when it comes to workplace safety, assessing hand functions and capabilities and designing safe and usable products [1 , 6].

To the authors’ knowledge, there are limited data on the strength capabilities of the Iranian population, particularly on the wrist torque strength. The findings from research in this area can fill the gaps in strength data for Iranians. These data can also provide valuable information for designers to design safe and usable products for the community or be used by occupational health and safety practitioners for the design and allocation of tasks. Therefore, the aims of the present study were to characterise the wrist U/R torque strength and to evaluate and the effects of individual differences (including age, gender, hand dominance and body mass index (BMI)) on the wrist U/R torque strength among the population of two major cities in the northwest of Iran.

2 Methods

2.1 Study design and procedure

The study was conducted in Tabriz and Zanjan cities in the northwest of Iran. The study period was between October and December, 2013. Recruitment locations were university buildings, schools, public and private offices and residential homes. Each participant signed a written consent form before participation in the study and was free to withdraw at any stage of the study. Approval for the study was obtained from the ethical review committee of the Tabriz University of Medical Sciences.

2.2 Participants

A total of 769 participants (391 males and 378 females) aged between 5 and 74 years took part in the study. The criteria used for the selection of participants in the study were being in a good general health without having any serious disease or musculoskeletal problems, particularly in their upper limbs. The sample size was determined using Morgan Table considering 95% confidence level and 5% marginal error and a total population size of 2081261 in Tabriz and Zanjan cities (based on Iranian Statistical Center). The sample size was determined to be 384 cases, but it was increased to 768 in view of the design effect of 2 for cluster sampling. The samples were proportionally allocated to Tabriz and Zanjan cities as 597 and 171 cases, respectively. Considering the equal number of males and females, the samples of each city allocated equally to both genders. The samples were also allocated proportionally to each age category.

2.3 Data collection

There were no suitable commercial instruments available to measure the wrist torque strength. Thus, a digital angle torque adaptor model AD2– 030 CU (Eclatorq Technology Co., Ltd., Taiwan) with a range of 1.5–30 N/m and a disc shaped handle were used for recording the torque strength data. The disc shapedhandle (with circular cross-section) had a diameter of 9 cm, which was selected according to the recommendations found in the literature [7, 8]. The disc shaped handle was attached to the torque meter shaft (Fig. 1(a)) and then they were mounted in a cylindrical case to simulate a jar-shaped measuring unit for the purpose of the study (Fig. 1(b)).

The wrist (U/R) torque measurements were carried out in accordance with the procedures described in the literature [1 , 9–11], as described below. The wrist torque measurements were recorded in a standing position turning the disc shaped handle in an anti-clockwise direction (such as when opening a jar) using one hand to create the torque and the other hand to hold the jar-shaped measuring unit. This represented ulnar torque for one hand and radial torque for the other. Measurements were performed for both dominant and non-dominant hands. The participants were instructed to exert their maximal voluntary strength for three seconds. No verbal encouragement or visual feedback regarding the participant’s performance was given during the experiments. Two repetitions of the wrist strength measurement were recorded for each condition and if the two measurements were within 10% of each other, they were considered valid; otherwise the measurement was repeated. The average value of the two consistent recordings was used in the subsequent analysis. A 2-minute rest break was given between successive measurements.

Additional data including age, gender, handedness, height and weight of the participants were also collected. The body weight and standing height were measured using a digital electronic scale (accurate to 0.01 kg) and portable stadiometer, respectively. Body mass index (BMI as weight/height²) was calculated from measurements of height and weight. All data were collected by the same investigator and during a single session.

2.4 Data analysis

Statistical analysis of the data including summarizing descriptive data was performed using SPSS software version 17.0 (SPSS Inc., Chicago, IL, USA). Demographic data and wrist strength characteristics of the study population were tabulated (as mean, standard deviation, range and percentiles). An independent sample t-test was used to evaluate the effect of hand dominance and gender on the wrist torque strength. One-way ANOVA with a between-subject design was used for evaluation of the effects of BMI and age on the wrist torque strength. Tukey’s post hoc tests were used to explore the effects in more details on the factors where significant effects were observed. In addition, Pearson’s correlation coefficient was used to evaluate the relationship between the wrist torque strength and BMI. A significance level of P < 0.05 was considered for all statistical tests.

3 Results

The main results of the study are presented in Tables 1 to 3 and in Fig. 2. Table 1 shows the wrist torque strength by gender and hand dominance. The results of the study showed significant differences in the wrist torque strength exertions between males and females (P < 0.001). For the dominant hand, the mean wrist torque strength exerted by males (4.5 N/m; SD = 1.59) was significantly higher than that exerted by females (3.4 N/m; SD = 0.88). Similarly for the non-dominant hand, males exerted higher wrist torque strength (4.1 N/m; SD = 1.18) than females (2.9 N/m; SD = 0.65). The results also showed that the mean wrist torque strength exertion with the dominant hand (3.9 N/m; SD = 1.42 N/m) was significantly higher than that exerted with the non-dominant hand (3.6 N/m; SD = 1.15 N/m) (P < 0.001).

The data on the wrist torque strength by gender and age of the participants are presented in Table 2. The results showed significant differences in the mean wrist torque strength values in terms of the age of the participants (P < 0.001). The results of Tukey’s post hoc test indicated that the mean wrist torque strength excreted by the age groups from 15 to 59 years were significantly higher than those exerted by the 5–9, 10–14 and ≥60 years age groups. No significant differences were found between the age groups from 15 to 59 years. It was also shown that the mean wrist strength exertions were significantly higher in males than in females for all age groups (P < 0.001), except for the 5–9 and 10–14 years age groups (Table 2 and Fig. 2).

Table 3 shows the wrist torque strength by gender and body mass index of the participants. The results of the study showed significant differences in the mean wrist torque strength values for bath males and females with respect to the BMI categories (P < 0.001). The mean wrist torque strength exertions by male and female participants with a lower body mass index (BMI < 19) were 2.4 (SD = 0.75) N/m and 2.1 (SD = 0.61) N/m, respectively. The mean wrist torque strength was increased to 5.2 (SD = 1.35) and 3.7 (SD = 0.79) for male and female participants with a higher body mass index (BMI >24), respectively. The results showed a significant positive association between the wrist torque strength and BMI for both males (r = 0.607; P < 0.000) and females (r = 0.522; P < 0.000).

4 Discussion

The present study was conducted to characterise the wrist U/R torque strength and to evaluate the individual differences in the torque strength among the population of two major cities in the northwest of Iran. The findings provide an insight into the strength capabilities of the Iranian population and can fill the gap in the strength data in Iran or used as a basic data in the field.

One of the main findings of the study was that the mean wrist torque strength exertion by males was higher than that exerted by females. The mean wrist torque strength of females was 75% of males’ strength, which is generally consistent with the findings of previous studies [7, 9]. The muscular strength of women, depending on the type of strength measure, muscle group and the population studied, is typically between 49% and 75% of men’s strength [5 , 12–14]. The muscular strength differences between males and females may originate from genetic differences in muscle mass or neuromuscular function (ability to recruit, stimulate, and synchronize motor units) or from culturally related behavioural differences in the amount of participation in strength developing activities, experience in maximal voluntary efforts or motivation to perform such trials [13].

As shown in this study, the mean wrist torque strength exertions with the dominant hand was higher than those exerted by the non-dominant hand. The mean wrist strength exertion with the dominant and non-dominant hands for the whole sample was 3.9 N/m and 3.6 N/m, respectively, which indicates 8% lower strength exertion for the non-dominant hand compared to the dominant hand. This is in agreement with previous reports that the strength of the dominant hand is approximately 3% to 10% stronger than of that of the non-dominant hand [6, 15]. The results also indicated that the strength differences between dominant and non-dominant hand for males and females were 9% and 14% , respectively. This result also supports the findings of previous research such as Nicolay and Walker [6], who reported that females can produce significantly greater force values with their dominant hand compared to their non-dominant hand than male subjects [6].

With regard to the body mass index, the results of study showed a higher level of wrist torque strength for those participants with a higher body mass index (BMI >24). The significant positive association between the wrist torque strength and BMI in this study is consistent with the findings of Madanmohan et al. [16], who reported significant positive association between hand strength and BMI for both males and females.

To the author’ knowledge, this is one of the first attempts to characterize the wrist U/R torque strength among Iranian population. However, care should be given when applying the findings of this study as the participants may not be the representative of the whole Iranian population. Therefore, further studiesconsidering various ethnic groups in the country are recommended. Also, further studies testing other strength measurements such as hand grip strength, pinch strength or other aspects of torque strength (such as wrist pronation/supination and extension/flexion strength) among Iranian population are worth investigating. As there are limited data on strength capabilities of Iranian population, further research in this area can fill the gaps in strength data for Iranian population and can provide valuable information for designers to design the safe and usable products for the community or be used by health and safety practitioners in the field.

5 Conclusions

The findings of the present study provide an insight into the wrist torque strength and individual strength differences among the population of two major cities in the northwest of Iran. The mean wrist U/R torque strength exertion by females was 75% of that exerted by males. The mean strength exertion with the non-dominant hand was 8% lower than strength exertion of the dominant hand. There was also a significant positive association between the wrist torque strength and BMI. This additional information on the wrist torque strength of the Iranian population can fill the gap in the strength data for Iranians, or used by health and safety practitioners in the field.

Footnotes

Acknowledgments

This project was funded by the Tabriz University of Medical Sciences. The authors would like to acknowledge all participants who collaborated in this study.

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