INVESTIGATION ON YOUNG ADULT HAND GRIP STRENGTH

It is believed that exposure to whole-body vibration (WBV) may increase seated occupant drowsiness and seated. The purpose of this paper is to investigate the strength of the hand grip among the young adults in Malaysia. Also, to examine the correlation between anthropometry factors such as hand length (HL), hand breadth (HB), wrist circumference (WC) and body mass index (BMI) with average full hand grip strength of young adults. 40 Malaysian young adults with equal females and males and the range age of 23 to 28 years old voluntarily basis participated in this study. Three experiments were conducted in sitting position according to American Standard Hand Therapist (ASHT) with 45o, 90o and 135o of hand flexion using dynamometer. The results show the significant different full hand grip strength between Malaysian young adult females and females, the difference full hand grip strength for different hand flexion angles in sitting position and difference correlations between anthropometry factors and full hand grip strength for both young adult males and females.


INTRODUCTION
Human hand grip strength is measured by the amount of static force that a hand can squeeze around a dynamometer commonly being quantified in kilogram, pounds, and millilitres of mercury or Newton. Hand grip strength is interpreted as a reliable measurement by using a standard and appropriate method with calibrated equipment. Repeated measures with standard positioning, instruction and hand grip strength calculation were executed.
Published normative data for hand grip strength are available from many regions such as West Bengal, India 1 , Kartaka, India 2 , South Africa, Africa 3 , Turkey 4 and Australia 5 . The existing data from previous studies are classified into age and gender subgroups. Analysis of hand grip strength by gender shows higher grip by male at all ages, and analysis by age group demonstrate a peak of grip strength among 40 years old, then gradually decline for both gender 5 . Grip strength is a predictive value to other health condition, although it is not a causative reconciliation. However, proved existing studies relating to the hand grip strength focused on gender groups in wider range of age classification which open the opportunity to study the hand grip strength for smaller range of age group such as young adults.
The study on small age range would produce significant effect for product design considerations.
A disparity occurs in the literature over a correlation of hand grip strength and BMI whereby many researchers claimed a positive correlation upon hand grip strength and BMI such as reported by Dhananjaya et.al 7 [11][12][13][14] but difficult to search and almost none on correlation between hand grip strength and other anthropometry data such as hand length (HL), hand breadth (HB) and wrist circumference (WC) among Malaysian young adult population.
The aim of this study is to investigate and analyse the recent data of hand grip strength among the young adults population in Malaysia. Next is to describe normative data of hand grip strength for Malaysian young adult population by establishing grip strength parameters such as HL, HB, WC and BMI correlation upon full hand grip strength performance using a dynamometer. The study also will investigate the full hand grip strength using different types of hand flexion angles in sitting position.

STATE OF THE ART
Hands are important body part to conduct various handling, pushing, pulling, gripping, carrying and lifting activities. Lam et.al reported that poor handling interaction between product or workstation and human could lead to low operation performance, risk the individual health and contribute to accident and poor safety as well 15 .There are many factors that influencing the hand grip strength such as health status, gripping time, age, gender, dietary status, hand movement, muscle activities and torment as suggested in Swanson et.al 16 .
Hand grip strength data is important in medical field such as indicator for body healthy, diagnose disease activity, proposing suitable treatment according to hand and recording muscle movements as studied by De et.al 1 . In addition, Putz found that hand grip strength also shows the fatigue seriousness 17 . In engineering application, Abdullah found that hand grip strength data is important to be accounted in developing and designing product, workstation, process and the related system to ensure the zero-working risk during machine-human interaction 18 .
The grip strength according to the posture and body joint angles and the maximum grip strength for optimal body posture and joint angle among 156 males and 224 females Bengalee adults with age range of 20 to 60 years old was examined by De et.al 1 . The study found that Bengalee males had a significantly greater (p<0.001) grip strength compared to that of Bengalee females. Also, the maximum grip strength was obtained in standing posture with elbow angle of 90 o in both Bengalee adult males and females. While Salam et.al 2 conducted an investigation to search the correlation between grip and pinch strength with body mass index among dental professionals in Karnataka, India. The study among 150 Indian professional dentals with range age of 22 to 40 years belong to both genders showed that there was a significantly weak positive correlation of body mass index with grip strength with r was equal to 0.233. Next, Ramlagan et.al 3 examined the hand grip strength in associated with social and health differences among 50 years old and above of 3840 South Africans.
The results from the study showed the mean overall of hand grip strength for African men with mean age 61.1 years old was 37.9 kgs while 31.5 kgs for African women with mean age 62.0 years old. It also reported that greater grip strength among African men was associated to greater height, not being underweight and lower functional disability while among African women, the greater grip strength was associated to greater height, better cognitive functioning, and lower functional disability. In another research, Ekşioğlu 4 studied the gender and age specific reference values for isometric hand grip strength of 128 males and 83 females' age between 18 to 69 years of Turkey population with special regard to occupational demand. The study found that mean and standard deviation of maximum static grip strength values for dominant and non-dominant hands respectively were 455.2 ± 73.6 N and 441.5 ± 72.6 N for Turkey males, and 258 ± 46.1 N and 246.2 ± 49.1 N for Turkey females. The mean Turkey female strength was about 57% of the Turkey mean male strength value for both dominant and non-dominant hands. There was a curvilinear relationship of grip strength to age, significant differences between genders, hands, and some age-groups, and a correlation to height, body-mass, BMI and hand dimensions depending on the gender. The similar scope of study also conducted by Shahida et.al 14 21 reported in his study that young adults were belonging to 17 to 40 years based on conception of adults' development. Therefore, this study considered the group age of 23 to 28 years as young adult according to thus researchers.

METHODS
This investigation was conducted among 20 young adult males and 20 young adult males. This small sample is enough to produce significant study as supported by Jason et.al 22 and Fagarasanu et.al 23 . The range age of the participants is between 23 to 28 years old. All participants are belonging to Asian people and Malaysian citizenship. The participants also free from musculoskeletal-related medical history in order to obtain the results that free influenced by health factor. All participants are voluntarily basis.
An electronic handgrip dynamometer with the maximum measurement for isometric forces up to 90kg/200lb and its sensitivity 0.1kg/0.2lb was used in this study to measure the hand gripping strength. An electronic weighing scale was used to measure the weight of participants and height measuring scale to measure the participants' height in order to calculate their body mass index (BMI). The hand length, breadth and wrist circumferences of the participants were measured by using tape measurement.
Participants were briefed regarding the study objectives and the investigation procedures. Then, participants were instructed to take a full meal before participating the experiment as conducted by Ekşioğlu 4 .
Next, participants were interviewed by facilitator in order to obtain the demographic and health information followed by data collecting activities on participants' weight, height, hand breadth, hand length and wrist circumference as shown in Figure 1. The measurement of participant's hand breadth was obtained by measuring the length between radial and ulnar metacarpals where the metacarpal heads from the second to fifth metacarpal while the hand length was measured from the line of middle finger to styloid process as referred to Shurrab et.al 25 . The wrist circumference was measured at the styloid process of the radius and ulna, with outstretch of the hand using the measurement tape as referred to Shurrab et.al 25 .
Next, before the maximum hand gripping strength was investigated, the temperature of the experiment room had been set up to 22ºC with normal humidity (40-60%) for all participants to avoid disturbance factors such as demotivated, outperform, competition, noise and spectators as conducted by Ekşioğlu 4 . The experiment was conducted in three modes of hand postures angles which were in 45 o , 90 o and 135 o as shown in Figure 2. For every experiment mode, the participants was asked to be sit on a provided chair that was set up according to American Standard Hand Therapist 25 to avoid the awkward sitting posture as shown in Figure 2. Then, the participants were asked to grip the handgrip dynamometer according to their comfortable griping to calibrate the dynamometer.

Figure 2: Experimental setup in investigating the hand grip strength among young adults
Next, the participants were instructed to grip the dynamometer using maximum strength to obtain the maximum hand gripping strength data for each determined hand posture angles. Two minute rest time was given to participant in between tested gripping modes. Generally, the experiment was taken approximately one hour per participant to be completed.
Finally, the hand grip strength data was recorded in commercial software and correlation analysis was conducted by using Minitab 17 software to study the significant correlation between the hand gripping strength for every hand flexion angles and the HL, HB and WC.   Table 1 summarizes the correlation coefficient, R between hand length (HL), hand breadth (HB) wrist circumference (WC) and body mass index (BMI) and the average full gripping strength of different hand flexion angles among young adults. The results for 45º of hand flexion shows that the full gripping strength for the young adult male participants are moderately correlated to the HL and the WC with the Rvalue is 0.5881 and 0.5085 each while for the young adult females, the full gripping strength is associated to the HB with R-value is 0.5456. The BMI factor is contributed to the weak correlation to the hand grip strength of young adults both for males and females with the R-value is 0.1884 and 0.2254 each.

RESULTS
The correlation results between HL, HB, WC and BMI and the full hand grip strength of 90º hand flexion shows the same pattern as 45º of hand flexion angle for both young adult males and females.
The correlation results for 135º of hand flexion angle shows that HL, HB and WC has weak correlation to the young adult males' full hand grip strength while HB has moderate correlation to the young adult females' full hand grip strength with R-value is 0.4903. However, most participants claimed that 135 o hand flexion is the simplest posture among three postures. The BMI factor also has weak correlations with the full hand grip strength in this 135 o hand flexion result.  The results in this study are significant in the human factors and ergonomics field by contributing the technical data for designing a product such as lifting mechanism 26 and working activities such as controlling a joystick to operate remote container crane 18 . Hand grip strength data also important in engineering application and product design and development because gripping activity is common and frequent action in handling objects and operations. Proper amount of hand grip strength will contribute many benefits to operators' health condition and safeties i.e. avoiding upper and lower body pains, reduce awkward posture risk, reduce working hazard, increases working performance and increase task ease 17 .