The demographic data for the study participants are summarized in Table 1. Notably, there were no significant differences in age, height, body mass, and BMI between the two groups.
Table 1
Participant demographics.
Variable | CON (N = 12) | CSP (N = 12) | P-value |
Mean ± SD | Mean ± SD |
Age (years) | 21.66 ± 2.01 | 23.25 ± 2.76 | 0.123 |
Height(cm) | 183.33 ± 12.82 | 182.58 ± 6.90 | 0.860 |
Body Mass (kg) | 78.50 ± 12.70 | 72.66 ± 8.74 | 0.204 |
BMI (kg.m2) | 23.33 ± 2.78 | 21.77 ± 2.08 | 0.134 |
VAS (mm) | N/A | 2.83 ± 0.83 | - |
NF, FT stands for No-Fatigue and Fatigue-Terminal condition respectively. CON, Control Group; CSP, Chronic Shoulder Pain Group; BMI, Body Mass Index; VAS, Visual Analogue Scale of Current Pain. ** statistically significant differences between the CON and CSP groups.
The results demonstrate that different fatigue conditions (non-fatigue and terminal fatigue) led to distinct kinematic effects during the performance of the repetitive pointing task (refer to Table 2 and Fig. 4). Specifically, fatigue-induced changes were evident in mean angles at all three joints. Notably, the mean angle for trunk lateral flexion in the CON group was greater after fatigue than before fatigue. Similarly, the CSP group exhibited a smaller mean angle after fatigue than before fatigue in the effect of time × group (p < 0.013). Additionally, the mean rotation angle for the trunk was greater before fatigue than after fatigue in the CON group, as indicated by the effect of time (p < 0.006) and the effect of time × group (p < 0.006). These changes imply that the trunk leaned less but rotated more toward the non-moving arm’s side after fatigue.
Turning our attention to the shoulder, we observed that the mean plane of elevation angle in the CON group before fatigue was smaller than after fatigue. Similarly, the CSP group also had a smaller mean angle before fatigue compared to after fatigue in the effect of time (p < 0.001). Shoulder elevation angle in both groups before fatigue was greater than after fatigue in the effect of time (p < 0.001) and the effect of time × group (p < 0.027). Additionally, the shoulder rotation angle in both groups before fatigue was greater than after fatigue in the effect of time (p < 0.030). These findings suggest that the humerus was less forward and less elevated after fatigue compared to the condition before fatigue.
Furthermore, the mean elbow flexion and rotation angles in both groups were also greater after fatigue than before fatigue in the effect of time (p < 0.006 and p < 0.001), indicating that, on average, the elbow was more flexed after fatigue.
Table 2
Joint angles result under all Conditions (NF vs FT) and Groups (CON vs CSP).
Variables | CON (N = 12) | CSP (N = 12) | Time Effect | Time × Group |
Mean ± SD | Mean ± SD |
NF | FT | NF | FT | F | P-value | ES | Power | F | P-value | ES | Power |
Trunk (degree) | X | 2.34 ± 0.99 | 3.38 ± 1.33 | 4.19 ± 1.50 | 3.36 ± 1.27 | 0.103 | 0.751 | 0.005 | 0.061 | 7.271 | 0.013** | 0.248 | 0.732 |
Y | 4.00 ± 0.87 | 2.66 ± 1.07 | 3.58 ± 1.44 | 3.59 ± 1.62 | 9.074 | 0.006** | 0.292 | 0.821 | 9.349 | 0.006** | 0.298 | 0.832 |
Z | 5.16 ± 2.67 | 6.58 ± 3.45 | 4.10 ± 2.21 | 3.84 ± 2.57 | 1.654 | 0.212 | 0.070 | 0.233 | 3.538 | 0.073 | 0.139 | 0.436 |
Shoulder (degree) | X | 41.56 ± 8.89 | 64.42 ± 8.77 | 35.87 ± 6.36 | 61.50 ± 9.76 | 111.314 | 0.001** | 0.835 | 1.000 | 0.363 | 0.553 | 0.016 | 0.089 |
Y | 63.88 ± 13.05 | 43.00 ± 3.41 | 65.21 ± 9.29 | 58.92 ± 13.54 | 19.344 | 0.001** | 0.468 | 0.987 | 5.579 | 0.027** | 0.202 | 0.617 |
Z | 17.14 ± 3.21 | 14.19 ± 1.87 | 19.35 ± 2.66 | 18.68 ± 2.68 | 5.376 | 0.030** | 0.196 | 0.601 | 2.149 | 0.157 | 0.089 | 0.289 |
Elbow (degree) | X | 68.64 ± 3.60 | 77.16 ± 9.51 | 66.30 ± 9.06 | 69.14 ± 9.87 | 9.265 | 0.006** | 0.296 | 0.829 | 2.315 | 0.142 | 0.095 | 0.307 |
Y | 3.14 ± 1.12 | 2.69 ± 1.07 | 3.36 ± 1.50 | 3.09 ± 2.01 | 0.728 | 0.403 | 0.032 | 0.129 | 0.048 | 0.829 | 0.002 | 0.055 |
Z | 54.45 ± 13.28 | 66.41 ± 6.88 | 58.59 ± 6.81 | 72.09 ± 9.04 | 18.415 | 0.001** | 0.456 | 0.984 | 0.068 | 0.796 | 0.003 | 0.057 |
NF, FT stands for No-Fatigue and Fatigue-Terminal condition respectively. Trunk x, y, and z angles are trunk lateral flexion, rotation, and flexion angles, respectively. Shoulder x, y, z angles are shoulder plane of elevation, elevation, and rotation angles, respectively, Elbow x, y, z angles are elbow flexion, abduction, and rotation angles, respectively. ES, Effect Size; CON, Control Group; CSP, Chronic Shoulder Pain Group. **indicates a statistically significant interaction effect for the ANOVA (p < 0.05).
The examination of joint angular variabilities (as detailed in Table 3 and Fig. 5), investigated the impact of fatigue on the trunk and upper limb movement patterns.
Trunk lateral flexion variability in the CON group increased after fatigue compared to the pre-fatigue condition. In contrast, the CSP group exhibited smaller variability after fatigue than before fatigue in the effect of time × group (p < 0.001). Additionally, trunk rotation variability in both groups was greater after fatigue than before fatigue (effect of time, p < 0.010). These increased trunk angular variabilities imply a less stable trunk movement pattern following shoulder fatigue.
After fatigue, the variability of the shoulder plane of elevation increased in both groups (effect of time, p < 0.001). This indicates altered shoulder movement patterns due to fatigue. Specifically, in the CON group, shoulder elevation angular variability after fatigue was greater than before fatigue. In contrast, the CSP group exhibited a decrease after fatigue compared to before fatigue in the effect of time (p < 0.030) and the effect of time × group (p < 0.005).
Elbow flexion variability in both groups increased after fatigue (effect of time, p < 0.001; effect of time × group, p < 0.001). Notably, in the CON group, elbow rotation variability before fatigue was greater than after fatigue. However, in the CSP group, it was greater after fatigue than before fatigue in the effect of time (p < 0.003) and the effect of time × group (p < 0.001). These findings highlight how fatigue at the trunk level can influence movement patterns of the distal joints (elbow) within the multi-joint linkage.
Table 3
Joint angular variabilities result under all Conditions (NF vs FT) and Groups (CON vs CSP).
Variables | CON (N = 12) | CSP (N = 12) | Time Effect | Time × Group |
Mean ± SD | Mean ± SD |
NF | FT | NF | FT | F | P-value | ES | Power | F | P-value | ES | Power |
Trunk (degree) | X | 0.96 ± 0.27 | 1.17 ± 0.23 | 1.57 ± 0.23 | 1.31 ± 0.07 | 0.215 | 0.647 | 0.010 | 0.073 | 16.443 | 0.001** | 0.428 | 0.972 |
Y | 0.83 ± 0.12 | 0.89 ± 0.26 | 0.74 ± 0.15 | 0.85 ± 0.12 | 7.833 | 0.010** | 0.263 | 0.763 | 0.561 | 0.462 | 0.025 | 0.111 |
Z | 0.84 ± 0.29 | 0.69 ± 0.31 | 0.81 ± 0.26 | 0.84 ± 0.31 | 0.484 | 0.494 | 0.022 | 0.102 | 1.185 | 0.288 | 0.051 | 0.181 |
Shoulder (degree) | X | 7.51 ± 1.75 | 8.38 ± 2.02 | 6.93 ± 0.67 | 8.65 ± 0.73 | 22.082 | 0.001** | 0.501 | 0.994 | 2.428 | 0.133 | 0.099 | 0.320 |
Y | 3.56 ± 1.05 | 4.04 ± 0.90 | 8.55 ± 2.05 | 5.39 ± 2.82 | 5.363 | 0.030** | 0.196 | 0.600 | 9.910 | 0.005** | 0.311 | 0.853 |
Z | 2.63 ± 1.06 | 2.38 ± 0.33 | 2.65 ± 0.87 | 3.16 ± 0.28 | 0.537 | 0.537 | 0.018 | 0.092 | 3.412 | 0.078 | 0.134 | 0.423 |
Elbow (degree) | X | 23.65 ± 1.38 | 32.26 ± 4.12 | 28.61 ± 1.13 | 31.05 ± 1.42 | 49.637 | 0.001** | 0.693 | 1.000 | 15.461 | 0.001** | 0.413 | 0.964 |
Y | 21.08 ± 0.10 | 21.07 ± 0.30 | 21.03 ± 0.36 | 21.14 ± 0.45 | 0.716 | 0.406 | 0.032 | 0.128 | 1.189 | 0.287 | 0.051 | 0.181 |
Z | 33.64 ± 4.00 | 25.97 ± 1.18 | 27.81 ± 3.29 | 29.32 ± 1.15 | 10.818 | 0.003** | 0.330 | 0.882 | 24.108 | 0.001** | 0.523 | 0.997 |
NF, FT stands for No-Fatigue and Fatigue-Terminal condition respectively. Trunk x, y, and z angles are trunk lateral flexion, rotation, and flexion angles, respectively. Shoulder x, y, z angles are shoulder plane of elevation, elevation, and rotation angles, respectively, Elbow x, y, z angles are elbow flexion, abduction, and rotation angles, respectively. ES, Effect Size; CON, Control Group; CSP, Chronic Shoulder Pain Group. **indicates a statistically significant interaction effect for the ANOVA (p < 0.05).
The investigation of mean CRPs and CRP variabilities (as detailed in Table 4 and Fig. 6), investigated how fatigue affects joint kinematics. Specifically, we examined the relationship between trunk flexion/extension and shoulder plane of elevation in both groups before and after fatigue.
Before fatigue, the mean CRP and CRP variability between trunk flexion/extension and shoulder plane of elevation exceeded the after-fatigue values (p < 0.037 and p < 0.011, respectively). This suggests altered coordination between trunk movement and shoulder elevation due to fatigue. Interestingly, in the CON group after fatigue, the CRP variability between trunk rotation and shoulder plane of elevation was greater than before fatigue. However, in the CSP group, this variability was greater before fatigue than after fatigue (effect of time × group, p < 0.027).
The mean CRP between trunk lateral flexion and shoulder elevation in both groups before fatigue exceeded the post-fatigue values (effect of time, p < 0.008). This indicates fatigue-induced changes in the alignment between lateral trunk movement and shoulder elevation. Furthermore, CRP variability in the CON group after fatigue was greater than before fatigue. In contrast, in the CSP group, this variability was greater before fatigue than after fatigue (effect of time × group, p < 0.013).
Table 4
Mean CRPs and CRP Variabilities under All Conditions (NF vs FT) and Groups (CON vs CSP).
Variables | CON (N = 12) | CSP (N = 12) | Time Effect | Time × Group |
Mean ± SD | Mean ± SD |
NF | FT | NF | FT | F | P-value | ES | Power | F | P-value | ES | Power |
ShPE-ElFl (degree) | Mean CRP | 5.23 ± 0.68 | 4.90 ± 0.45 | 5.49 ± 0.92 | 5.22 ± 0.80 | 4.942 | 0.037** | 0.183 | 0.566 | 0.055 | 0.816 | 0.003 | 0.056 |
Variability | 0.90 ± 0.08 | 0.92 ± 0.09 | 1.12 ± 0.21 | 1.01 ± 0.28 | 3.446 | 0.077 | 0.135 | 0.427 | 5.043 | 0.035** | 0.186 | 0.574 |
TrFl-ShPE (degree) | Mean CRP | 5.33 ± 0.88 | 4.42 ± 0.63 | 5.33 ± 0.71 | 5.19 ± 0.60 | 7.745 | 0.011** | 0.260 | 0.758 | 4.230 | 0.052 | 0.161 | 0.503 |
Variability | 0.91 ± 0.17 | 0.87 ± 0.04 | 0.91 ± 0.11 | 0.94 ± 0.09 | 0.058 | 0.812 | 0.003 | 0.056 | 1.055 | 0.315 | 0.046 | 0.166 |
TrRo-ShPE (degree) | Mean CRP | 5.30 ± 0.98 | 4.99 ± 0.53 | 5.26 ± 0.59 | 5.00 ± 1.07 | 2.200 | 0.152 | 0.091 | 0.295 | 0.018 | 0.894 | 0.001 | 0.052 |
Variability | 0.93 ± 0.21 | 0.97 ± 0.08 | 1.19 ± 0.16 | 1.04 ± 0.30 | 1.860 | 0.186 | 0.078 | 0.257 | 5.647 | 0.027** | 0.204 | 0.622 |
TrLaFl-ShEl (degree) | Mean CRP | 5.15 ± 0.54 | 4.81 ± 0.70 | 5.20 ± 0.60 | 4.50 ± 0.59 | 8.631 | 0.008** | 0.282 | 0.802 | 1.097 | 0.306 | 0.047 | 0.171 |
Variability | 0.87 ± 0.06 | 0.90 ± 0.13 | 1.04 ± 0.16 | 0.88 ± 0.16 | 2.826 | 0.107 | 0.114 | 0.362 | 7.361 | 0.013** | 0.251 | 0.737 |
NF, FT stands for No-Fatigue and Fatigue-Terminal condition respectively. ShPE-ElFl, TrFl-ShPE, TrRo-ShPE, and TrLaFl-ShEl indicate CRP between trunk flexion/extension and shoulder plane of elevation, CRP between trunk flexion and shoulder plane of elevation, CRP between trunk rotation and shoulder plane of elevation, CRP between trunk lateral flexion and shoulder elevation, respectively. ES, Effect Size; CON, Control Group; CSP, Chronic Shoulder Pain Group. **indicates a statistically significant interaction effect for the ANOVA (p < 0.05).
Regarding the coefficient of variability of the EMG signals (as presented in Table 6 and Fig. 7), we observed that the coefficient of variability of the Lower Trapezius muscle in both groups increased after fatigue compared to the pre-fatigue condition. Specifically, this increase was significant in terms of both the effect of time (p < 0.001) and the effect of time × group (p < 0.028). Furthermore, we also found that the variability of the Biceps Long Head muscle in both groups was greater after fatigue than before fatigue, as indicated by the effect of time (p < 0.002).
Table 6
Coefficient of variability (CV) of the EMG signal result under all Conditions (NF vs FT) and Groups (CON vs CSP).
Variables | CON (N = 12) | CSP (N = 12) | Time Effect | Time × Group |
Mean ± SD | Mean ± SD |
NF | FT | NF | FT | F | P-value | ES | Power | F | P-value | ES | Power |
DeltA (% CV) | 23.00 ± 3.64 | 22.00 ± 2.49 | 23.66 ± 6.62 | 25.00 ± 5.92 | 0.176 | 0.676 | 0.008 | 0.069 | 0.488 | 0.492 | 0.022 | 0.103 |
TrapL (% CV) | 6.83 ± 3.78 | 12.83 ± 3.73 | 4.91 ± 2.77 | 7.00 ± 3.56 | 23.635 | 0.001** | 0.518 | 0.996 | 5.549 | 0.028** | 0.201 | 0.615 |
BicLong (% CV) | 5.41 ± 1.72 | 7.00 ± 3.01 | 3.66 ± 1.15 | 5.83 ± 2.20 | 12/493 | 0/002** | 0/362 | 0/922 | 0/302 | 0/588 | 0/014 | 0/082 |
TriLong (% CV) | 4.00 ± 1.53 | 3.58 ± 2.23 | 3.41 ± 1.31 | 2.66 ± 1.07 | 2/015 | 0/170 | 0/084 | 0/274 | 0/689 | 0/698 | 0/007 | 0/067 |
NF, FT stands for No-Fatigue and Fatigue-Terminal condition, respectively. DeltA, Deltoid Anterior; TrapL, Lower Trapezius; BicLong, Biceps Long Head; TriLong, Triceps Long Head, respectively. ES, Effect Size; CON, Control Group; CSP, Chronic Shoulder Pain Group. **indicates a statistically significant interaction effect for the ANOVA (p < 0.05).