Effects of Elbow Flexion on the Hand-Grip Strength

Introduction

The hand is the most important work tool for the human. The grip is the action of grasping an object by hand and holding it firmly. The hand grip strength is the ability in forceful flexion of all finger joints with the maximum voluntary force that the subject is able to exert. Grip strength is used as an objective index of the functional integrity of the upper extremity [1]. Manjula, et al. [2] have performed a review of literature on grip strength. Some researchers have reported strong correlations between grip strength and various anthropometric factors, such as weight, height body surface area and hand length [3, 4, 5, 6]. Khan, Ansari, and Agrawal [7] reported declining hand-grip strength is associated with increase in the body mass index (BMI).

Sartorio, et al. [8] reported increase in the grip strength with age advancement in children, and boys showed greater hand-grip strength than the girls. Smrithi, et al. [9] reported positive correlation between hand-grip strength and weigh and BMI only in females and between hand- grip strength and weigh, height and BMI of males, but negative correlation between hand-grip strength and the weight in overweight male subjects. Mathiowetz, Rennells, and Donahoe [10] reported that grip-strength was higher with the elbow positioned in 90° of flexion as compared with when the elbow was positioned in full extension. Interestingly, the grip strength has been reported to be higher in dominant hand for the right- handed individuals, but no such significant differences could be detected for the left-handed subjects [11].

Objectives

participants (222 males and 125 females) of ages 22.6±3.5 years. The subjects were volunteer college students whom were recruited by senior and graduate students performing a mini-project, as a required laboratory activity in an ergonomics course. The data were compiled from the student mini-projects over a multiple number of years. A standardized data collection form was provided to each experimenter to record each subject’s physical characteristics (i.e., gender, age, weight, height, and handedness), and the hand grip strength data. The physical characteristics of the subjects are summarized in Table 1.

The primary objective of this study was to explore the effects of elbow flexion on the hand-grip strength. In addition, the study sought to investigate the correlation between HGS and the physical characteristics (i.e., gender, weight, height and handedness).

Results

Table 2: The mean and standard deviation of the grip strength (in kg force) at various elbow flexion levels for the female, male and all subjects. The elbow positions associated with the highest measured grip strength values were tallied. As shown in Table 3 for the dominant hand and Table 4 for the non- dominant hand, about a 50% of subjects (both female and male) achieved their greatest grip strength with the elbow in a fully extended position (i.e., in a 0° flexion). The results also revealed that about 27% of the subjects had their highest grip strength with the elbow in the 90° flexed position. Some subject had their greatest grip strengths at a multiple elbow positions. This explains why the percentages add up to more than 100%. As can be seen in Table5, the same pattern was found when the grip strength in both hands of each subjects were averaged.

A pair-wise comparison, using the Student’s T-Test, was used to statistically analyze the differences in the hand-grip strengths at the five elbow positions. The results of the comparisons are summarized in Table 6 for the dominant hand, Table 7 for the non-dominant hand, and Table 8 for both hands averaged grip strength achieved at the 120°, 90°, 60°, 30° and 0° elbow flexion levels. The comparison test results showed the same patterns of consistent differences in the grip strengths in the dominant, non-dominant and the average for both hands for each pair of elbow positions.

Table 8: Pairwise comparison of both-hands averaged grip strength at various elbow flexions. Note: BHG90° (for example) designates the mean both-hand averaged grip strength in the 90° elbow flexion. Values in the parentheses are the 95% confidence interval between means of grip strength in the pair of compared elbow flexions Based on the results, as presented in Tables 6-8, the effects of the elbow flexion levels are grouped and presented in Table 9.

between the two genders regarding their grip strength (Table 11). On an average basis, the females had about 41% lower grip strength than the male subjects.

Conclusion

The results of this study revealed that the greatest hand grip strength is attained when the elbow is held in the fully extended position (no flexion). This is probably due to the fact that the muscles are not loaded for holding an object away from the body, which increases torque in the hand-arm joint that must be counter-acted by the muscles for maintaining the state of equilibrium. However, holding the elbow in an extended position and hanging the arm on the side of the body may not be practical for performing most types of work and daily activities. As the results of study revealed, performing the grip exertion task in the 90° flexed elbow position is the next desirable elbow posture, in which the grip strength was found to be statistically significantly higher than the strength obtained in any other elbow flexed positions. The results of this study also showed that, on an average, the grip strength of the dominant hand was found to be significantly higher than that of the non- dominant hand. However, no significant difference was found for the dominant and non-dominant hands regarding at which elbow position the highest grip strength is achieved. This study showed that the grip strength of the female subjects was significantly lower than that obtained by the male subjects. On an average, the female group had about 41% lower grip strength than the male subjects.