The subjects were selected randomly from different districts, i.e. Paschim Medinipur, Purba Medinipur, and Purulia of West Bengal state, India. The study was conducted on 380 adult subjects (156 male and 224 female) having the age range of 20 years to 60 years. The present study was approved by the Human Ethical Committee of the institution, and the experiment was performed in accordance with the ethical standards of the committee and with the Helsinki Declaration. All the subjects volunteered for the present study. From all the subjects consents were taken according to the rules of the institution.

The static grip strength measurement has been performed by having the subjects’ maximal grip by using Lafayette (USA) hand grip dynamometer. This hand grip dynamometer features a dual pointer system to retain the maximum effort. The testing range on a dual scale is (0-100) kg / (0-220) lb. The subject was asked to squeeze the dynamometer as hard as possible without moving the rest of the body. Reading was taken from the dynamometer scale, when the pointer no longer moved (Dhara et al, 2009) and thus the grip strength were measured for both the hands.

The grip strength was evaluated with the variation of posture as well as body joint angles. Experiments were performed on three main postures, viz., standing, sitting, and lying as well as in different arm positions and during adopting forwarding bend posture. In sitting posture the grip strength was measured in two different conditions:

Sitting without elbow rest: Seated in a chair with elbows unsupported forming an angle of 90°.

The arms positions and bend posture was defined by joint angle as explained below:

The arm was hanging normally beside the body with an elbow angle of 180° approximately.

The grip strength was tested for both the right and left hands.

Three readings were taken in each position with a time gap of 1 minute. A rest of 5 minutes was given between two postures while recording the strength. Three trials were given on both the hands. The maximum value was taken in kilogram. The average value was not taken because problem could arise due to fatigue of the muscle (Haidar et al, 2004).

Data were summarized into mean and standard deviation values using Microsoft Excel. The level of significance of difference between group means was determined performing t-tests (Das and Das, 2004). The ANOVA study and post-hoc analysis were made by the use of ORIGIN 6.1 software.

The mean value of the hand grip strength of adult male and female subject was higher in the right hand in comparison to left hand in different postures and in different body joint angles. As the right hand of the subjects was the dominant hand, the subjects showed greater grip strength in that hand than that in the non-dominant hand, which might be because of difference in muscle strength between two hands. Incel et al (2002) also reported that the hand grip strength is to be higher in dominant hand with right handed subjects, but no such significant differences between sides could be documented for left handed people. However, Bagi et al (2011) noted greater grip strength in the dominant hand both in cases of right hander and left handers. Kamarul (2003) found that although the right hand is approximately 10% stronger than the left (12.1% in male and 11.0% in female) there is a variance of between 9.1 to 9.6% in different individuals. A general rule is often used to suggest that dominant hand is about 10% stronger than the non-dominant hand (Petersen et al, 1989; Armstrong and Oldham, 1999). Our findings were also supported by the work of O’Driscoll et al. (1992), and Richards et al (1996). They reported higher grip strength values in the dominant hand compared to the non-dominant hand. However, there was a disagreement with above finding with that of the work done by Reikeras (1983) and Harkonen et al (1993) who reported that there was no significant difference in grip strength of dominant hand and non dominant hand. According to Rabergs and Roberts (1997), one explanation for the differences in grip strength may be due to the use of more muscle and muscular hypertrophy in the dominant hand which leads to increased strength.

The result of this study indicated that grip strength of adult males in different postures and different body joint angles was significantly greater (p<0.001) than the grip strength of adult female in both right and left hands. One possible explanation for this finding was the difference in the type of activity of each gender. Male are more active than female and perform more physical work. Sometimes males are involved in more weight handling than their female counterpart. The differences in body composition may be another factor. Strength variations between men and women may be mainly related to the smaller amount of absolute muscle mass (about 60% of men) and a higher body fat percentage in women (Janssen et al, 2000). Besides genetic effects this might be caused by a weaker affinity to strength-demanding tasks in women. It must be taken into account that women are 40% to 60% weaker in the upper body and about 25% to 30% in the lower body than men (Shephard, 2000; Kraemer et al, 2001). These regional differences occur due to different muscle mass distributions and different day-to-day activities (Janssen et al, 2000; Miller et al, 1993). Leyk and co-workers (2006) investigated some 2000 age-matched young men and women with regard to their maximum handgrip strength. 90% of the female subjects produced maximal handgrip forces smaller than 95% of their male counterparts.

The results regarding the effect of posture on grip strength in male and female subjects indicated that there was no significant difference of grip strength among different postures. However, the mean grip strength was slightly higher in standing posture than that in the other postures. Teraoka (1979), who studied the effects of different body positions on grip strength, also found that grip strength measured in standing was the strongest, whereas grip strength measured in supine was the weakest. Balogun et al (1991) also demonstrated that grip strength was greater in standing posture as compared to the supine and sitting positions. Richards (1997) found no difference in grip strength measured in either sitting or supine postures. Similar findings were also evident in the present study and therefore support the findings of the above researchers.

Variation of body joint angles had some effects on grip strength in adult male and female. The mean value of the hand grip strength in elbow 90 degree angle of adult male and female subjects was higher, although non-significantly, in both right and left hand. A possible reason may be that the grip strength is directly related to forearm muscle (flexor muscle). Flexor muscle originates from lower part of the humerous which is above the elbow joint. So, the elbow position may have significant effect on grip strength (Su et al, 1994a). Earlier, Mathiowetz et al (1985) also studied the effect of elbow position on grip strength and found it to be higher with the elbow flexed at 90° while Su et al (1994b) found that the highest mean grip strength score was obtained with the elbow fully extended.

In the present study, although no significant difference in grip strength with the variation of shoulder positions was observed, yet it was slightly observed to be higher in shoulder 180° position. Su et al (1994b) compared the grip strength at 0°, 90° and 180° of shoulder flexion in standing. They found that the strongest grip was produced when the shoulder was in 180° of flexion with elbow fully extended whereas the weakest grip was associated with 0° of shoulder flexion. Coincidentally, 0° of shoulder flexion with 90° of elbow flexion was the recommended testing position by the American Society of Hand Therapists for grip strength measurement (Fess and Moran, 1981). Contrary to the above findings, Mathiowetz et al (1985) demonstrated that grip strength was significantly stronger at 90° of elbow flexion than at full extension. This finding was supported by a report that grip strength was greater at 90° of elbow flexion than at either full extension or 120° of flexion (Fan et al, 1999). Kumar et al (2008) suggested that grip endurance training can be undertaken with the elbow in 90° of flexion or full extension.

A wrist position also affects grip strength. It was observed in the present study that the wrist neutral position showed significantly higher grip strength than that of ulnar deviation. Ridan et al (2000) stated that higher values of strength were noted in such configuration of the upper limb where the elbow joint was straight. On the other hand grip reduction in grip force was reported with wrist flexion (Halpern and Fernandez, 1996; Kattel et al, 1996; Claudon, 1998). Lamorean and Hotler (1995) also observed that radial and ulnar deviation caused a reduction in grip strength. Pronation of the forearm has also been shown to reduce grip force, but the effects of supination are less clear (De Smet et al, 1998; Mogk and Keir, 2003). Slightly different observations were noted by other workers. Fong and Ng (2001) and Barr et al (2001) reported that grip strength is the highest with the wrist in 15° or 30° of extension and 0° of unlar deviation. However, Pryce (1998) found no significant differences between any combination of 0° or 15° of wrist extension and ulnar deviation. Mogk and Keir (2010) demonstrated that the forearm posture only affected grip force when the wrist was flexed.

A significant variation in grip strength was observed between trunk neutral and trunk flexion positions. Similar variation was also noted by other groups of workers. Debeliso et al (2004) showed that trunk extension strength was significantly greater than trunk flexion strength. The trunk flexion strength of both women and men with bent working postures of the back was 98% of the strength of those who had no bent postures at work. The trunk extension strength on the other hand was 92% for women and 98% for men of the strength of those in the groups with bent back postures compared to those who had no bent back postures (Nygard et al, 1988). Significant differences in trunk strength (isometric torque) were found between males and females, at various sagittal plane trunk postures, and between flexion and extension tasks (Keller and Roy, 2002).

Grip strength measured at standing posture was higher than that of other postures. Although there was no significant difference in hand grip strength between two angles of elbow joints, i.e., 90° and 180°, yet it was higher at the elbow joint angle of 90°. Similarly the grip strength of right and left hand showed slightly higher value at the shoulder joint angle of 180° although there was no significant difference between two shoulder joints angles (90° and 180°). However, the hand grip strength was significantly higher in wrist neutral position and trunk neutral position than that of wrist unlar deviation and trunk flexion respectively. From our study it may be recommended that for Bengalee (Indian) population the hand grip strength should be measured in the following standardized posture: the subjects should adopt standing posture with an angle of 90 degree at elbow joint and 180 degree at shoulder joint and the trunk and wrist should be at neutral positions. These findings highlight the importance for clinicians to adopt a standard testing position to assess grip strength in adult Bengalee population. This study also possesses important application in the use of grip strength during operation of different instruments in different postures and arm positions.