To assess the function in patients with upper limb injuries, it is essential to measure the normal values based on anatomical and biomechanical knowledge of the normal upper limb and hand. Various measurement methods exist, including grip strength and pinch strength, flexion and extension of the wrist, pronation and supination of the forearm, and flexion and extension of the elbow. Numerous studies have been published on the hand grip and pinch strength [1-4] and the range of motion of the forearm [5-7], but most efforts to establish normative values for forearm rotational force have been conducted on Western populations [8-11], and there are no existing studies on Korean populations. Recognizing the importance of forearm torque, not just hand strength, is crucial for assessing upper limb function and setting appropriate therapeutic goals and directions by establishing normative values for healthy individuals. The purpose of this study is to measure forearm rotation torque in healthy Korean adults using a torque gauge and to provide an objective standard for assessing patients with hand disorders and forearm injuries, particularly those with distal radioulnar joint arthritis or triangular fibrocartilage complex (TFCC) injuries, as well as for evaluations before and after treatment.

The average rotational torque value for supination of the dominant hand was measured at 33.00±11.57 kgf•cm (3.36±1.18 N•m), and for pronation at 32.38±12.01 kgf•cm (3.30±1.22 N•m) (Table 1), with a statistically significant greater force in supination. Similarly, for the nondominant hand, supination also showed a significantly greater force compared to pronation. When comparing the dominant and nondominant hands, the dominant hand showed higher forces in both supination 33.00±11.57 kgf•cm (3.36±1.18 N•m) and pronation 32.38±12.01 kgf•cm (3.30±1.22 N•m) compared to the nondominant hand’s supination 31.31±11.19 kgf•cm (3.19±1.14 N•m) and pronation 30.03±12.16 kgf•cm (3.06±1.24 N•m), and these differences were statistically significant (Table 2, Fig. 3).

For individuals with a dominant left hand, statistically significant differences were found in both pronation and supination forces (Table 3).

In males, the dominant hand’s pronation force was 41.45±10.19 kgf•cm (4.11±1.03 N•m), which was higher than its supination force of 41.12±9.96 kgf•cm (4.19±1.01 N•m). For the nondominant hand, the supination force was 40.28±9.96 kgf•cm (4.22±1.01 N•m) higher than the pronation force of 39.23±10.68 kgf•cm (4.00±1.08 N•m). However, for females, both the dominant and nondominant hands showed higher forces in supination at 27.26±8.88 kgf•cm (2.78±0.90 N•m) and 24.98±8.46 kgf•cm (2.54±0.86 N•m), respectively, compared to their pronation forces of 25.98±9.20 kgf•cm (2.65±0.93 N•m) and 23.54±8.35 kgf•cm (2.40±0.85 N•m) (Table 4, Fig. 4).

Age-wise, males in their 20s to 29s (3rd decade) showed the highest forces in both pronation and supination for dominant and nondominant hands, while females peaked in their 40s to 49s (5th decade). When combining data for males and females, the highest average forces for both pronation and supination in dominant and nondominant hands were found in the 30s to 39s (4th decade) (Table 5, Fig. 5).

According to the results of the age-based analysis of variance, both the supination torque (F=8.25, p<0.001) and pronation torque (F=6.85, p<0.001) in the dominant hand showed significant differences. Additionally, significant sex-based differences were also observed (Table 6).

Injuries to the forearm and wrist can impact the torque of forearm rotation [10]. It has been stated that a decrease in forearm rotational torque is directly related to the functionality of the forearm [11]. Recent reports indicate that forearm torque plays a crucial role in the diagnosis of injuries to the TFCC [12,13], and the degree of forearm rotational torque is clinically significant in evaluating the effectiveness of postsurgical treatment [13].

We believe that in order to establish a standard, it is necessary to first conduct research on the normal values of forearm rotational torque. Previous studies that have presented normal values of forearm rotational torque [8-11] were all conducted in Western countries. According to the literature, there are significant differences in muscle strength between Asians and other ethnic groups, and it is known that Asian women are more susceptible to muscle loss compared to other ethnicities [14,15]. Therefore, we think it is necessary to study the normal values according to age and sex among Koreans. All subjects in this study were Korean.

Various factors, such as measurement posture and equipment, can influence the assessment of forearm rotational force. Timm [8] noted that among methods using cylinder, screwdriver, and doorknob handles, the doorknob handle allows for the measurement of the strongest force. In this study, we used a T-shaped handle, which is easily obtainable and conveniently connected to a torque gauge. Haugstvedt et al. [16] found that changing the forearm position to neutral, supination, and pronation showed that the forearm’s neutral position is the most efficient and reliable. Axelsson and Kärrholm [17] compared sitting and standing positions in measuring rotational force and found no difference in measurements, emphasizing the importance of maintaining a consistent posture. Accordingly, we measured pronation and supination forces with the elbow flexed at 90 degrees and the forearm and wrist in a neutral position.

Comparing our measurements with previous studies, Rey et al. [18] reported an average supination torque of 8.9 Nm and pronation torque of 5.3 Nm in a study of the French population using a shovel handle, measuring 99 individuals. Wong and Moskovitz [19] in the United States, using a doorknob handle, reported average supination and pronation torques of 3.3 Nm and 3.5 Nm, respectively. Axelsson et al. [11] reported supination torque of 7.2 Nm and pronation torque of 6.1 Nm in a study involving 499 Swedes using a shovel handle. In this study, we obtained supination torque of 3.36 Nm and pronation torque of 3.30 Nm using a T-shape handle.

Given the influence of the handle type on measurements as noted in previous studies, subsequent research could provide more information and enable comparisons of forearm torque norms across ethnicities by varying the type of handle among the same group of participants.

This study aimed to present the normal values of pronation and supination forces according to age, sex, and hand dominance, but it had limitations. Out of 500 participants, 485 (97%) were right-hand dominant and only 15 (3%) were left-hand dominant, indicating a very low number of left-hand dominant individuals. Globally, the proportion of left-hand dominant individuals is known to be about 10% to 12%, but in populations from East Asian cultures, including Korea, where right-hand dominance has been historically enforced, the proportion is reported to be about 1% to 10% [20,21]. The 3% in this study may also reflect some sampling bias. However, considering the increasing societal acceptance of left-hand dominance, it is expected that the proportion of left-hand dominant individuals may increase in future studies.

Moreover, the study showed a higher proportion of females to males, 6 to 4, in the 50s and 60s age groups, suggesting the possibility of sex-related bias in the results of this age segment. Future studies should consider stratifying by sex when recruiting participants. Additionally, the study did not analyze differences in results based on physical characteristics like height and weight, which is a limitation. These physical characteristics can influence the results, so future research should include these variables for a more accurate study design.

While there was no statistical difference between pronation and supination torque in Koreans with p>0.05, the rotational torque of the dominant hand was found to be significantly stronger than that of the nondominant hand. Additionally, among Koreans, the age group showing the highest average rotational torque was 30 to 39 years.

The average forearm rotational torque values in healthy Korean adults can serve as valuable reference data for assessing functional recovery following upper extremity injuries. In particular, they can be effectively utilized for evaluating pre- and post-treatment outcomes in cases of distal radioulnar joint arthritis and TFCC injuries.