Hundred sixty-six women and thirty-five men participated in the study; 92% of the participants were right-handed. The volunteers were students of Health Sciences careers from a university. None of the participants reported musculoskeletal disorders nor were any missing data in the intra-evaluation reproducibility measurements collected (Table 1).
Table 1. Characteristics of the participants
Taking into account that three measurements were taken in each posture, the difference between the highest measurement achieved in the three attempts and the average value of the three attempts was compared. No statistically significant differences were noted in this comparison in any of the positions, so the results are reported using the average value of the three measurements.
When comparing the average HS between the right and the left side of each of the postures, it was found that the muscular strength of the dominant limb was of a statistically significant higher value (Table 1). Reproducibility was nearly perfect in all the positions evaluated for both the upper right and left limbs (Table 2). Regarding the level of agreement for the comparison between the sitting and supine positions with a flexed elbow, an average difference of −0.406 was noted, and the upper and lower agreement limits were found to be 4.592 and −5.404, respectively. For supine position with an extended elbow and supine position with a flexed elbow, the average difference was −1.479, and the upper and lower agreement limits were 3.881 and −6.840, respectively (Figure 1).
Table 2. Reproducibility test, the reassessment of prehensile strength in three positions
Figure 1. Level of agreement between a. Sitting versus supine position with a flexed elbow, b. Supine position with an extended elbow and supine position with a flexed elbow.
The position recommended by the American Society of Hand Therapists for assessing hand grip dynamometry is a sitting position, with a neutral shoulder position, the elbow flexed at 90°, and the forearm and wrist in neutral positions (18). Most studies perform hand grip dynamometry evaluation in this position (20); however, this position is not always possible to assume when the measurement is taken at the hospital level, due to situations associated with the patient’s health condition.
The posture of the body and the position of the shoulder, elbow and wrist, influence prehensile strength (21,22). This study evaluated HGD agreement between sitting and supine positions with a flexed and extended elbow. Results showed no significant differences in the measurements between these two positions, which suggests that for patients who cannot assume a sitting posture, measurement taken in the supine position will be equally reliable in determining the level of HGD. In other words, both postures can be interchangeably used since they produce a similar result.
In this study, no differences were noted between HGD values when taking measurements in the sitting position or the supine position with an elbow flexed (see Table 1). Although Murugan et al. and Elsais et al. reported a higher value of strength in the sitting position, it was not statistically significant compared with the supine or standing positions (22,23). These findings can be explained by strength variations associated with the planes in which the movement is performed and to the effect of gravity on the segments involved.
Regarding the position of the elbow flexed at 90° compared with the extended elbow in the supine position, this study showed a greater HGD value with the elbow in extension (see Table 1). These results are consistent with those reported by España-Romero et al. (21) and Limbasiya et al. (24). This can be explained by the fact that an extended position has a more favorable length–tension relationship for the forearm muscles. According to the biomechanical analysis, the flexor digitorum superficialis is the only finger flexor muscle that crosses the elbow joint, which means that the position of this joint can affect the muscle strength developed. As the elbow flexes, the muscle proximally shortens and is mechanically disadvantaged, which decreases its ability to generate tension and, therefore, a better contraction strength (25). However, despite showing a greater HS value in the position with the extended elbow, this difference does not affect the results obtained for reproducibility and limits of agreement; thus, these positions may be interchangeable.
In the present study, differences between HS were identified by gender and dominance; 92% of participants showed right-hand dominance. This is consistent with reports from other studies such as the meta-analysis performed by Dodds et al. (20), in which the most frequently evaluated hand is the right and/or the dominant hand, as reported in literature. The dominant hand has a higher HS value, which is associated with the greater use that the person makes of that hand. However, the difference between the strength exerted by men and women is also described in literature (20,22). In this study, a greater number of women were evaluated, who presented a lower HGD value as opposed to the men that were evaluated, regardless of their posture or position.
When comparing the HS obtained in the sitting position with a flexed elbow, the supine position with a flexed elbow and the supine position with an extended elbow, this study found no differences between the values obtained with HGD (Table 1). This finding is reported in literature (22,23,26), considering that the effect of body posture and joint position has a low impact on the prehensile strength that is not clinically significant.
Regarding the reproducibility between the three positions, the coefficients were nearly 1, which means that reproducibility is almost perfect; therefore, the positions can be interchangeable. However, the reproducibility coefficient does not provide information on the pounds of strength variability between measurements. The level of agreement primarily describes the average result from differences obtained between the three positions, which is important when deciding which position would bring less variability in a clinical setting.
If the muscular strength determined in each posture is similar or equal, the average difference would be expected to be very close to zero. Therefore, a graphical analysis allows for these differences to be quantified and for the upper and lower limits of these differences to be established (Figure 1). In the present study, these differences may be determined by a true variance, which may be related to a change in muscle strength in each participant derived from the change in posture, as well as variability recorded by the evaluator and random error.
According to the graphical analysis performed by Bland and Altman (Figure 1), it can be shown that the average difference is nearly zero, which indicates that the difference in muscle strength determined by the three positions is approximately 1.5 pounds of strength, which could be considered acceptable for a measurement that can calculate approximately 23 pounds of strength. The maximum acceptable difference in muscle strength between the three positions should be considered a clinical interpretation rather than a statistical one (27).
Another important aspect of measurement variability lies in the analysis of the limits of agreement, which shows the maximum and minimum ranges of measurement variation, which ranged from 3.8 to −6.8 between the sitting and supine positions with an extended elbow, and from 4.5 to −5.4 between the sitting and supine positions with a flexed elbow. These limits show a maximum variability of up to 10 pounds of strength when the positions are compared, which means that the measurement between the two positions compared can vary by approximately 10 pounds. On the basis of the above-mentioned terms, in a clinical or research scenario, this would mean that minor changes of approximately 10 pounds of strength could be solely attributed to chance (27).
This study did not determine the reproducibility of the test reassessment. It is suggested that future studies should evaluate the variability for each test, which could be a criterion for choosing one of the three positions in cases where it is possible.