A total of 22 healthy individuals participated in the current investigation (11 men and 11 women, all right-handed) with an average age of 19.0 ± 0.3 years, a weight of 57.6 ± 1.9 kg, and a height of 168.4 ± 1.5 cm. The Edinburgh Handedness Inventory was used to gauge the handedness of each participant (Oldfield, 1971). The laterality quotient was ≥60 (laterality quotient: 90.5 ± 2.5). The adults were untrained for the activity and did not exhibit any neuromuscular abnormalities.

The joint position sense test system (JPSS, HLTX Technologies, Beijing, China) is a motion study system that has been utilized for measuring joint angles. The JPSS is small (38 × 33 × 20 mm), lightweight (30 g), and ambulatory (i.e., it can be employed anywhere and at any time and is not limited to a specific measurement volume in a laboratory). A JPSS connected to the hand was utilized to calculate the joint angles of the wrist given its three-dimensional orientation. A line was drawn from the wrist’s midpoint to the tip of the index finger to ensure proper alignment. The wireless JPSS sensor’s base was placed on the flat dorsum of the wrist, and its lower edge was positioned away from the wrist and along this line. Before conducting experiments, the device was validated, and the manufacturer calibration settings were employed. Some studies performed with JPSS have shown satisfactory reliability (Cutti et al., 2008; Parel et al., 2012; van den Noort et al., 2014; Li et al., 2015, 2019, 2020a; Marini et al., 2017). The JPSS sampling frequency used in this investigation was 50 Hz.

With the aid of an electronic digital force dynamometer, strength tests were conducted (grip analyzer; HLTX Technologies, Beijing, China; Figure 1). The instrument was calibrated in accordance with the manufacturer’s recommendations. Prior testing was also carried out to avoid errors. The grip span of the dynamometer was set at 5.0 cm. Inelastic metal support (Figure 1A) was added to the electronic digital force dynamometer during the MVIC test, and 0% MVIC grip force was added during the wrist joint position reposition tests (Figure 1 Set 1). It was removed when the grip force was maintained at 15% MVIC during the wrist joint position sense test (Figure 1 Set 2). When the grip distance was 5.0 cm (touching black sponge, Figure 1D), the grip strength was adjusted to 15% MVIC by turning the knob (Figure 1C) to adjust the spring (Figure 1B). The sampling frequency for this study was set at 100 Hz.

To guarantee optimal concentration, this exam was conducted in a quiet room. The participants had a head-mounted display fitted (V-8, Beimu Technologies, Shenzhen, China; Figure 2B). The participant saw the target angle (red line) and the real-time wrist joint angle (black line; Figure 2C), while the display restricted visual feedback from hand motion.

The individuals sat in a chair and then adopted a full body position in a line, with the upper arm adjacent to the body, the forearm placed on a horizontal platform (Figure 2A) or unsupported (Figure 3A), and the wrist in neutral positions (Figures 2H, K, 3B). To guarantee consistency in wrist placement between trials, the forearm firmly rested on the brace (Figure 2E; van den Noort et al., 2014) during wrist extension (Figure 2L), flexion (Figure 2M), radial deviation (Figure 2I), and ulnar deviation (Figure 2J) but was unsupported during pronation (Figure 3C) and supination (Figure 3D). The JPSS was fastened to the participant’s hand using a cushioned, nonelastic strap (Figure 2D). The data were collected and analyzed utilizing a computer, a modified MVIC test, and a joint position sense test program (HLTX Technologies, Beijing, China).

Prior to testing, the participants engaged in a warm-up activity. The warm-up exercise included three repetitions of reaching the dynamometer’s submaximal grip force (Jansen et al., 2008). They were instructed to utilize a hand grip and apply the strongest possible grip pressure on the dynamometer. The maximum result from the second test was reported as the grip strength (Bao and Silverstein, 2005). In addition, the participants were given 2 min to relax in between tests to reduce the effect of fatigue on the research results.

The computer screen was displayed in the head mounted display synchronously. The testing protocol was completely illustrated to participants when they watched the visible output via the head mounted display. One screen with a black line and a red line was shown to participants through the C++ software environment. The black and red lines indicate the wrist joint position and target position, respectively, for a certain trial. All tests started with the joint in the start position (Figures 2H, K, 3B). Participants moved their wrist joint until the black line was inside the red line, showing that the wrist joint had achieved the target position T. Participants were told to hold the target wrist position for 3 s, merely focusing on the wrist joint position. After the participants were kept in the target position for 3 s, the red line disappeared, and a voice programmed into the computer software instructed the participants to rest and move their joint to the start position. The participants tried to regain the target position using no visualization after 3 s. The participants pressed the footswitch with their right foot after establishing that the wrist joint was in the desired position (Figure 2G), and the computer recorded the reproduced position as Ri (i = 1,2,3) in the i-trial (Figure 4). The test was conducted thrice. This process was explained to the participants with a demonstration, and they conveniently sensed the process. Practice trials were repeated to enhance the participants’ confidence in performing the task successfully. The target positions (pronation 24°, supination 24°, radial deviation 16°, ulnar deviation 16°, extension 32°, and flexion 32°) and grip force (0 and 15% MVIC) were randomly assigned. The participants held an electronic digital force dynamometer (Figure 2F) in their hands without any extra force when the grip force was 0% MVIC. Low force levels (15% MVIC) were chosen to minimize muscle fatigue (Marini et al., 2017; Naderi et al., 2020). Additionally, some reports states that most everyday manual activities are performed in low force levels (Kotani et al., 2000). To maintain attention on the task during the experiment, the participants rested for 3 min after 9 trials.

Three methods were used to evaluate the position reproduction errors: (1) absolute error (AE), which corresponds to overall error; (2) constant error (CE), which corresponds to error directionality (under- or overestimation); and (3) variable error (VE; for precision), which corresponds to variation in error levels across trials. The following formulas were used to calculate these values:

where the force reproduced during the ith trial is denoted by Ri, the target force is denoted by T, the maximum voluntary isometric contraction is denoted by MVIC, and the mean force reproduced over the course of three trials is denoted by.

The sex differences in MVIC values were compared using the independent t-test. Mixed-model ANOVAs were utilized as well to examine the effects of position (pronation 24°, supination 24°, radial deviation 16°, ulnar deviation 16°, extension 32°, and flexion 32°), force level (0 and 15% MVIC), and sex (men and women) on AE and VE; in this model, sex was regarded as a between-participants component, while position and force level were considered within-participants variables. Significant effects were rechecked based on extra comparisons, and the post hoc least significant difference (LSD) test was applied for multiple comparisons. Additionally, one-sample t-tests were performed to compare constant error values for each direction and force level to 0 to identify the trials in which participants produced excessive or insufficient movement. The statistical analysis was carried out using SPSS 22.0 (IBM, Armonk, NY, USA). The level of statistical significance was set at a P-value < 0.05, and all results are shown as the mean and standard deviation ( ± SD).

The findings demonstrated considerably elevated grip forces in men (359.4 ± 23.1 N) compared to women [247.0 ± 16.4 N, t(20) = 3.964, P < 0.001]. The 15% MVIC of men (53.9 ± 3.5 N) was also higher than that of women [37.0 ± 2.5 N, t(20) = 4.016, P < 0.001].

Mixed-model ANOVA was employed to compute the absolute error, demonstrating no significant interaction among sex, wrist position, grip force, F(5,100) = 1.056, P = 0.389, sex and grip force, F(1,20) = 0.038, P = 0.848, sex and wrist position, F(5,100) = 0.709, P = 0.618, or wrist position and grip force, F(5,100) = 1.549, P = 0.182. For absolute error, the wrist position [F(5,100) = 10.358, P < 0.001] and grip force [F(1,20) = 5.303, P = 0.032] had highly significant effects, but sex did not [F(1,20) = 1.018, P = 0.325]. There were significantly higher absolute error values at 15% MVIC (3.8 ± 0.3°) than at 0% MVIC grip force [3.1 ± 0.2°, t(20) = 2.303, P = 0.032; Figure 5]. There were significantly higher absolute error values at flexion (5.3 ± 0.7°) than at pronation [3.2 ± 0.3°, t(20) = 2.902, P = 0.009], supination [3.6 ± 0.3°, t(20) = 2.727, P = 0.013], radial deviation [2.0 ± 0.2°, t(20) = 5.431, P < 0.001], ulnar deviation [2.9 ± 0.2°, t(20) = 3.990, P < 0.001], and extension [3.7 ± 0.4°, t(20) = 3.110, P = 0.006]. There were significantly lower absolute error values at radial deviation than those at pronation [t(20) = −3.404, P = 0.003], supination [t(20) = −4.834, P < 0.001], ulnar deviation [t(20) = −3.617, P = 0.002], extension [t(20) = −5.256, P < 0.001], and flexion [t(20) = −5.431, P < 0.001].

Mixed-model ANOVA was used to compute the variable error, revealing no significant interaction between sex, wrist position, and grip force, F(5,100) = 0.548, P = 0.740, sex and grip force, F(1,20) = 0.027, P = 0.870, sex and wrist position, F(5,100) = 0.348, P = 0.882, or wrist position and grip force, F(5,100) = 0.729, P = 0.604. For variable error, the wrist position [F(5,100) = 6.446, P < 0.001] had highly significant effects, but not sex [F(1,20) = 0.014, P = 0.906], and grip force [F(1,20) = 0.526, P = 0.477]. There were significantly lower variable error values at radial deviation (1.4 ± 0.1°) than those at pronation [2.0 ± 0.2°, t(20) = −3.035, P = 0.007], supination [2.5 ± 0.3°, t(20) = −4.317, P < 0.001], extension [2.2 ± 0.2°, t(20) = −3.454, P = 0.003], and flexion [2.5 ± 0.2°, t(20) = −5.988, P < 0.001]. There were significantly lower variable error values at ulnar deviation (1.7 ± 0.2°) than those at supination [t(20) = −2.935, P = 0.008] and flexion [t(20) = −3.932, P < 0.001]. There were significantly higher variable error values at flexion than those at pronation [t(20) = 2.163, P = 0.043; Figure 6].

Significantly lower constant error values were detected at grip force at 0% MVIC of grip force in radial deviation [−1.2 ± 0.4°, t(21) = −3.124, P = 0.005], ulnar deviation [−1.7 ± 0.5°, t(21) = −3.211, P = 0.004], extension [−1.7 ± 0.7°, t(21) = −2.524, P = 0.020], and flexion [−3.8 ± 0.8°, t(21) = −4.987, P < 0.001] and 15% MVIC of grip force in ulnar deviation [−1.6 ± 0.6°, t(21) = −2.702, P = 0.013], extension [−2.0 ± 1.0°, t(21) = −2.100, P = 0.048], and flexion [−4.4 ± 1.2°, t(21) = −3.750, P = 0.001]. Moreover, estimations were most accurate for wrist joint position at 0 [−0.8 ± 0.7°, t(21) = −1.157, P = 0.260] and 15% MVIC [−0.4 ± 0.7°, t(21) = −0.547, P = 0.590] of grip force in pronation, 0 [−0.3 ± 0.6°, t(21) = −0.469, P = 0.644], and 15% MVIC [1.4 ± 0.9°, t(21) = 1.450, P = 0.162] of grip force in supination, and 15% MVIC [−0.2 ± 0.4°, t(21) = −0.651, P = 0.522] of grip force in radial deviation (Figure 7).

Our study has some limitations. For example, only healthy adult subjects with a mean age of 19.0 years were enrolled in this study. Therefore, the conclusions in the study may only be valid for the assessment of the wrist joint position sense in similarly aged and healthy adult. Thus, additional studies are needed to examine these relationships among other demographics. In addition, there are only two grip force (0 and 15%MVIC) in this study. To check if the relationship between the grip force and wrist position sense likely to be linear or if are there non-linearities, other grip forces (e.g., 30 or 50% MVIC) influence wrist position are needed. Our study has limitations and such grip forces (i.e., 30 or 50% MVIC) are needed in future studies.