3.1 Comparison of the ground reaction forces
As shown in Table 2 and Fig. 3, during ELS, the GRF of the professional group was significantly higher than that of the amateur group in the vertical, anterior–posterior (ant–post), and medial–lateral (med–lat) directions (P<0.01).
Table 2. Mean and standard deviation (mean ± SD) of the maximum ground reaction force (GRF) during seven sets of motions. Units: N/BW
|
Groups
|
WOF
|
LF
|
RBB
|
PB
|
PPS
|
ELS
|
SKR
|
F(x)
|
Amateur
|
0.43 ±0.08
|
0.38 ±0.11
|
0.50 ±0.15
|
0.61 ±0.23
|
0.99 ±0.83
|
0.80 ±0.85
|
0.26 ±0.07
|
|
Professional
|
0.51 ±0.10
|
0.42 ±0.12
|
0.45 ±0.06
|
0.51 ±0.11
|
1.71 ±1.04
|
2.03 ±1.00**
|
0.36 ±0.21
|
F(y)
|
Amateur
|
9.47 ±2.53
|
10.03 ±1.13
|
10.89 ±0.83
|
10.73 ±1.02
|
12.23 ±1.53
|
10.71 ±2.10
|
5.56 ±0.45
|
|
Professional
|
9.73 ±0.77
|
10.13 ±0.37
|
10.20 ±0.28
|
10.12 ±0.56
|
11.29 ±1.18
|
13.05 ±1.66**
|
5.74 ±1.84
|
F(z)
|
Amateur
|
1.20 ±0.28
|
1.15 ±0.33
|
1.11 ±0.42
|
1.29 ±0.57
|
1.45 ±0.40
|
1.39 ±0.32
|
0.89 ±0.15
|
|
Professional
|
1.42 ±0.21
|
1.15 ±0.30
|
1.03 ±0.25
|
0.92 ±0.26
|
1.95 ±0.67
|
2.22 ±0.67**
|
0.96 ±0.94
|
∗∗ P<0.01 and ∗P<0.05 represent the comparison between the professional group and the amateur group; the X-axis is the sagittal axis, the Y-axis is the vertical axis, and the Z-axis is the frontal axis.
3.2 Comparisons of three joint angles of the lower extremities
As shown in Table 3 and Fig. 4, during WOF, the knee flexion/extension angle, hip flexion/extension angle, hip abduction and rotation angle of the professional group were significantly larger than those of the amateur group (P<0.01).
During LF, the knee flexion/extension angle, hip abduction and rotation angle of the professional group were significantly larger than those of the amateur group (P<0.01), while the hip flexion/extension angle of the professional group was also larger (P<0.05).
During RBB, the ankle flexion/extension angle and knee flexion/extension angle of the professional group were significantly larger than those of the amateur group (P<0.01).
During PB, the ankle flexion/extension angle, knee flexion/extension angle and hip rotation angle of the professional group were significantly larger than those of the amateur group (P<0.01).
During PPS, the knee flexion/extension angle was significantly larger than that of the amateur group (P<0.01).
During ELS, the knee flexion/extension angle and hip rotation angle of the professional group were significantly larger than those of the amateur group (P<0.01).
During SKR, the hip flexion/extension angle of the professional group was significantly larger than that of the amateur group (P<0.01).
Table 3. Mean and standard deviation (mean ± SD) of the maximum joint angle of the hip, knee and ankle during the seven sets of motions. Units: N/BW
Joint angle
|
Group
|
WOF
|
LF
|
RBB
|
PB
|
PPS
|
ELS
|
SKR
|
Ankle flex/ext
|
Amateur
|
18.35 ±8.47
|
14.65 ±6.24
|
13.27 ±5.57
|
7.97 ±5.43
|
17.90 ±10.04
|
13.02 ±9.09
|
12.65 ±8.34
|
Professional
|
21.87 ±13.00
|
17.51 ±11.08
|
28.42 ±12.72**
|
21.29 ±13.10**
|
17.42 ±10.31
|
12.57 ±7.77
|
14.76 ±7.74
|
Knee flex/ext
|
Amateur
|
52.34 ±18.15
|
63.29 ±14.26
|
81.37 ±12.67
|
72.33 ±18.97
|
71.02 ±16.31
|
61.11 ±18.12
|
59.99 ±31.69
|
Professional
|
75.80 ±13.52**
|
97.49 ±19.76**
|
109.07 ±10.96**
|
98.53 ±16.75**
|
90.89 ±14.76**
|
84.20 ±11.86**
|
75.08 ±30.57
|
Hip flex/ext
|
Amateur
|
26.08 ±13.04
|
41.57 ±11.12
|
23.80 ±16.93
|
23.87 ±10.71
|
32.45 ±9.82
|
33.98 ±11.42
|
41.97 ±15.02
|
Professional
|
50.46 ±17.75**
|
54.35 ±13.14*
|
36.44 ±11.09
|
31.79 ±10.52
|
36.25 ±11.38
|
45.58 ±11.88
|
70.28±20.25**
|
Hip abduction
|
Amateur
|
10.51 ±5.54
|
16.59 ±5.62
|
17.53 ±9.24
|
15.81 ±6.14
|
29.71 ±5.16
|
24.94 ±9.23
|
14.26 ±9.38
|
Professional
|
30.54 ±16.04**
|
23.68 ±5.90**
|
24.53 ±6.50
|
19.55 ±7.24
|
32.92 ±9.69
|
31.61 ±4.73
|
17.40 ±10.74
|
Hip rotation
|
Amateur
|
11.02 ±10.41
|
19.15 ±11.68
|
23.44 ±12.55
|
23.41 ±11.52
|
27.43 ±9.75
|
17.56 ±6.88
|
13.40 ±6.36
|
Professional
|
33.26 ±10.85**
|
37.97 ±15.90**
|
35.20 ±8.17
|
36.78 ±8.63**
|
34.91 ±12.47
|
35.77 ±11.17**
|
18.97 ±10.04
|
∗∗ P<0.01 and ∗P<0.05 represent comparisons of the amateur group and professional group. flex/ext: flexion/extension
3.3 Comparisons of the net joint reaction force of the three joints of the lower extremities
The joint reaction forces exerted on the ankle, knee and hip joints are shown with peak values in Table 4 and Fig. 5, where the X, Y, and Z axes represent the med–lat, vertical, and ant–post directions, respectively.
In terms of hip joints, during SKR, the hip joint reaction force of the professional group in the med–lat direction was higher than that of the amateur group (P<0.05); during WOF, LF, and RBB, the hip joint reaction forces of the professional group were significantly higher than that of the amateur group in both the vertical and ant–post directions (P<0.01).
In terms of knee joints, during LF, RBB, PB, PPS, and ELS, the knee joint reaction force of the professional group was significantly higher than that of the amateur group in the vertical direction (P<0.01), whereas no significant differences existed in the med–lat and ant–post directions.
In terms of ankle joints, during RBB, PB, and PPS, the ankle joint reaction forces of the professional group were significantly higher than that of the amateur group in the vertical direction (P<0.01), whereas no significant differences existed in the med–lat and ant–post directions.
Table 4. Mean and standard deviation (mean ± SD) of the maximum joint force of the hip, knee and ankle during the seven sets of motions. Units: N/BW
Joint force
|
Group
|
WOF
|
LF
|
RBB
|
PB
|
PPS
|
ELS
|
SKR
|
Hip
|
X-axis
|
Amateur
|
-0.77 ±0.48
|
-1.02 ±0.70
|
-0.62 ±0.34
|
-0.57 ±0.26
|
-0.73 ±0.27
|
-1.22 ±0.98
|
4.96 ±3.46
|
|
|
Professional
|
-0.12 ±0.09
|
-0.75 ±0.46
|
-0.47 ±0.28
|
-0.75 ±0.98
|
-0.67 ±0.42
|
-0.55 ±0.57
|
10.69 ±5.51*
|
|
Y-axis
|
Amateur
|
30.69 ±16.19
|
29.95 ±13.20
|
30.06 ±15.55
|
57.49 ±24.09
|
87.98 ±53.09
|
51.98 ±23.40
|
14.16 ±8.60
|
|
|
Professional
|
74.62 ±39.66**
|
76.95 ±41.47**
|
117.53 ±99.00**
|
75.37 ±26.89
|
101.67 ±63.09
|
70.97 ±27.00
|
23.95 ±12.77
|
|
Z-axis
|
Amateur
|
4.10 ±3.90
|
3.56 ±3.43
|
2.41 ±1.83
|
13.50 ±9.17
|
23.48 ±20.15
|
9.35 ±5.52
|
1.93 ±0.95
|
|
|
Professional
|
20.75 ±14.30**
|
21.28 ±6.39**
|
27.41 ±12.58**
|
27.00 ±14.12
|
32.86 ±19.21
|
12.99 ±3.87
|
2.85 ±1.47
|
Knee
|
X-axis
|
Amateur
|
-2.18 ±3.63
|
-1.73 ±0.85
|
-0.82 ±0.42
|
-0.90 ±0.41
|
-0.46 ±0.21
|
-3.96 ±1.18
|
-1.35 ±0.64
|
|
|
Professional
|
-0.56 ±2.37
|
-1.15 ±0.32
|
1.80 ±1.14
|
-1.03 ±1.16
|
0.05 ±0.02
|
0.46 ±0.13
|
-3.77 ±1.79
|
|
Y-axis
|
Amateur
|
2.83 ±1.46
|
2.39 ±1.39
|
4.70 ±3.03
|
3.85 ±2.24
|
7.43 ±3.91
|
6.56 ±3.54
|
0.81 ±0.17
|
|
|
Professional
|
3.73 ±3.11
|
7.32 ±2.95 **
|
10.85 ±4.80**
|
8.07 ±3.92 **
|
11.58 ±1.91**
|
11.24 ±3.92**
|
1.69 ±1.15
|
|
Z-axis
|
Amateur
|
-0.99 ±1.05
|
-0.49 ±0.85
|
-0.02 ±0.01
|
-0.04 ±0.03
|
0.10 ±0.01
|
-5.57 ±4.53
|
-0.37 ±0.43
|
|
|
Professional
|
0.32 ±0.43
|
0.15 ±0.11
|
-0.05 ±0.03
|
-0.26 ±0.14
|
0.11 ±0.07
|
0.02 ±0.02
|
-1.59 ±1.21
|
Ankle
|
X-axis
|
Amateur
|
1.26 ±1.06
|
1.76 ±1.52
|
4.25 ±1.83
|
4.58 ±1.88
|
3.72 ±1.29
|
3.01 ±1.79
|
6.95 ±2.67
|
|
|
Professional
|
3.13 ±2.86
|
3.54 ±2.90
|
4.74 ±1.67
|
3.91 ±2.55
|
4.35 ±1.24
|
5.40 ±3.49
|
6.52 ±0.95
|
|
Y-axis
|
Amateur
|
13.65 ±5.81
|
13.42 ±4.37
|
19.11 ±10.25
|
18.62 ±7.78
|
90.45 ±28.76
|
60.94 ±22.12
|
21.48 ±17.27
|
|
|
Professional
|
18.29 ±8.06
|
18.37 ±13.23
|
34.77 ±15.92**
|
23.07 ±13.20**
|
148.97 ±30.94**
|
87.42 ±33.65
|
10.65 ±7.90
|
|
Z-axis
|
Amateur
|
-1.04 ±1.44
|
-1.31 ±1.09
|
-0.08 ±0.11
|
-0.15 ±0.10
|
-0.08 ±0.10
|
-8.87 ±2.05
|
-0.05 ±0.10
|
|
|
Professional
|
-0.11 ±0.20
|
-0.20 ±0.21
|
-0.05 ±0.09
|
-0.37 ±0.74
|
-0.07 ±0.18
|
-6.17 ±2.14
|
-2.39 ±6.92
|
∗∗ P<0.01 represents comparisons between the amateur group and the professional group. The X-axis is the sagittal axis, the Y-axis is the vertical axis and the Z-axis is the frontal axis.
3.4 Comparisons of net joint torque of the three joints in the lower extremities
As shown in Table 5 and Fig. 6, during RBB, hip abduction torque, hip flexion/extension torque and knee flexion/extension torque of the professional group were significantly larger than those of the amateur group (P<0.01), while hip rotation torque of the professional group was larger, but not significantly, than that of the amateur group (P<0.05).
During PB, the hip abduction torque, hip flexion/extension torque and ankle flexion/extension torque of the professional group were significantly larger than those of the amateur group (P<0.01).
During ELS, the hip flexion/extension torque and knee flexion/extension torque of the professional group were significantly larger than those of the amateur group (P<0.01).
During the remaining four sets of motions, there were no significant differences between the two groups’ net joint torque of the three joints.
Table 5. Mean and standard deviation (mean ± SD) of the maximum joint torque of the hip, knee and ankle during the seven sets of motions. Units: N/BW
Joint torque
|
Group
|
WOF
|
LF
|
RRB
|
PB
|
PPS
|
ELS
|
SKR
|
Hip abduction
|
Amateur
|
0.28±0.10
|
0.28±0.22
|
0.61±0.23
|
0.55±0.26
|
1.00±0.23
|
0.89±0.36
|
0.27±0.12
|
|
Professional
|
0.41±0.13
|
0.53±0.27
|
1.26±0.76**
|
0.90±0.26**
|
1.25±0.71
|
1.04±0.21
|
0.21±0.10
|
Hip rotation
|
Amateur
|
0.19±0.08
|
0.21±0.14
|
0.10±0.09
|
0.11±0.09
|
0.32±0.18
|
0.25±0.11
|
0.09±0.04
|
|
Professional
|
0.34±0.24
|
0.20±0.07
|
0.35±0.19*
|
0.08±0.04
|
0.51±0.23
|
0.42±0.21
|
0.08±0.04
|
Hip flex/ext
|
Amateur
|
0.40±0.17
|
0.39±0.37
|
0.30±0.17
|
0.32±0.24
|
0.64±0.33
|
0.09±0.07
|
0.38±0.13
|
|
Professional
|
0.38±0.14
|
0.36±0.23
|
1.37±1.06**
|
0.59±0.25**
|
0.81±0.42
|
0.88±0.83**
|
0.37±0.04
|
Knee flex/ext
|
Amateur
|
0.39±0.24
|
0.28±0.20
|
0.10±0.01
|
0.09±0.01
|
0.20±0.11
|
0.36±0.29
|
0.29±0.19
|
|
Professional
|
0.53±0.46
|
0.33±0.26
|
0.54±0.08**
|
0.18±0.12
|
0.22±0.10
|
0.44±0.45**
|
0.34±0.26
|
Ankle flex/ext
|
Amateur
|
0.32±0.28
|
0.44±0.36
|
0.90±0.38
|
0.57±0.21
|
0.94±0.24
|
0.70±0.29
|
0.66±0.14
|
|
Professional
|
0.55±0.34
|
0.57±0.45
|
0.91±0.23
|
0.76±0.09**
|
0.86±0.21
|
0.92±0.38
|
0.51±0.36
|
∗∗ P<0.01 and ∗ P<0.05 represent comparisons of the amateur group and the professional group.
3.5 Comparisons of lower extremity muscle strength
Table. 6 and Fig. 7 compared the lower extremity muscle strength between two groups during seven sets of motions.
During WOF, the professional group showed significantly more strength than the amateur group for the tibialis anterio, tibialis posterior, and gastrocnemius (P<0.01).
During LF, the professional group showed significantly more strength than the amateur group for the rectus femoris, vastus lateralis, vastus medialis, gluteus minimus, tibialis anterio, and gastrocnemius (P<0.01).
During RBB, the professional group showed significantly more strength than the amateur group for the rectus femoris, vastus medialis, biceps femoris, iliacus, gluteus maximus, gluteus minimus, and adductor longus (P<0.01).
During PB, the professional group showed significantly more strength than the amateur group for the iliacus and sartorius (P<0.01).
During PPS, the professional group showed significantly more strength than the amateur group for the rectus femoris, vastus lateralis, vastus medialis, iliacus, and gluteus minimus (P<0.01).
During ELS, the professional group showed significantly more strength than the amateur group for the biceps femoris, iliacus, adductor longus, and sartorius (P<0.01).
During SKR, the professional group showed significantly more strength than the amateur group for the iliacus (P<0.01).
Table 6. Mean and standard deviation (mean ± SD) of muscle strength during the seven sets of motions. Units:N/BW
Muscles
|
Group
|
WOF
|
LF
|
RBB
|
PB
|
PPS
|
ELS
|
SKR
|
Rectus femoris
|
Amateur
|
3.28±1.31
|
2.77±1.47
|
8.27±3.59
|
7.05±2.10
|
8.47±2.64
|
8.23±2.60
|
1.70±1.43
|
|
Professional
|
3.95±2.14
|
5.85±3.50**
|
11.86±3.07**
|
8.55±3.05
|
13.10±2.80**
|
10.71±3.66
|
3.84±2.86
|
Vastus lateralis
|
Amateur
|
10.86±4.70
|
10.19±5.50
|
25.50±11.30
|
24.53±8.18
|
28.82±10.56
|
30.57±12.25
|
6.72±4.95
|
|
Professional
|
11.70±9.51
|
23.73±10.35**
|
36.25±12.75
|
29.58±14.26
|
44.81±6.48**
|
38.88±16.06
|
2.73±2.57
|
Vastus medialis
|
Amateur
|
5.63±2.74
|
5.04±2.73
|
13.15±6.81
|
12.92±2.86
|
15.18±5.33
|
16.10±6.32
|
3.30±2.42
|
|
Professional
|
7.10±5.37
|
12.09±4.59**
|
22.16±7.14**
|
15.86±8.69
|
24.97±4.30**
|
22.15±8.40
|
1.35±1.27
|
Biceps femoris
|
Amateur
|
3.12±2.28
|
4.72±2.95
|
2.10±0.79
|
3.66±2.90
|
5.38±3.46
|
1.74±0.73
|
4.24±2.50
|
|
Professional
|
5.12±2.29
|
5.11±2.96
|
10.92±10.17**
|
4.83±2.66
|
8.29±5.02
|
3.92±1.18**
|
4.19±2.70
|
Iliacus
|
Amateur
|
2.65±1.58
|
2.17±1.05
|
2.29±1.36
|
1.59±0.99
|
3.75±4.26
|
1.57±1.45
|
0.95±0.86
|
|
Professional
|
2.43±1.19
|
2.15±0.66
|
7.61±6.09**
|
3.15±0.88**
|
7.76±2.98**
|
5.69±2.19**
|
2.64±1.67**
|
Gluteus maximus
|
Amateur
|
7.99±4.74
|
8.20±4.45
|
3.72±2.23
|
8.76±7.09
|
15.75±8.13
|
13.46±4.58
|
3.82±2.21
|
|
Professional
|
11.50±5.61
|
13.47±7.32
|
18.65±15.01**
|
11.53±18.03
|
18.89±8.35
|
15.96±6.63
|
1.85±1.43
|
Gluteus minimus
|
Amateur
|
1.77±1.03
|
1.87±1.77
|
3.73±1.99
|
3.30±1.06
|
5.88±1.88
|
5.21±1.86
|
0.86±0.57
|
|
Professional
|
2.89±1.06
|
3.84±1.87**
|
8.29±3.41**
|
3.93±2.91
|
9.21±3.83**
|
6.96±2.93
|
1.02±0.80
|
Sartorius
|
Amateur
|
1.83±0.91
|
1.55±1.28
|
1.38±0.41
|
1.35±0.74
|
2.14±1.74
|
1.00±0.87
|
1.30±0.69
|
|
Professional
|
1.85±0.51
|
2.04±0.51
|
2.54±0.55
|
5.00±1.24**
|
3.43±2.59
|
3.56±1.59**
|
1.69±0.79
|
Adductor longus
|
Amateur
|
0.68±0.76
|
0.95±0.70
|
0.70±0.39
|
0.66±0.44
|
2.00±1.45
|
0.71±0.44
|
0.47±0.31
|
|
Professional
|
1.11±0.88
|
0.40±0.26
|
3.57±2.82**
|
1.24±0.71
|
2.67±0.95
|
3.29±2.24**
|
0.51±0.45
|
Tibialis anterior
|
Amateur
|
0.81±0.53
|
1.94±1.64
|
0.16±0.10
|
0.21±0.13
|
5.42±4.12
|
5.45±4.73
|
1.33±0.86
|
|
Professional
|
4.87±4.30**
|
4.85±2.71**
|
0.80±1.32
|
0.39±0.27
|
4.85±1.32
|
7.63±2.10
|
3.04±1.82
|
Tibialis posterior
|
Amateur
|
0.05±0.01
|
0.62±0.49
|
1.43±0.67
|
0.22±0.41
|
1.30±0.90
|
1.72±1.35
|
1.11±0.32
|
|
Professional
|
0.50±0.46**
|
0.89±0.73
|
1.98±1.11
|
0.54±0.27
|
1.42±1.32
|
2.34±1.32
|
1.07±0.92
|
Gastrocnemius
|
Amateur
|
1.86±0.31
|
3.49±2.53
|
19.35±10.79
|
16.27±7.26
|
14.03±5.00
|
10.82±6.84
|
8.47±2.87
|
|
Professional
|
12.25±3.38**
|
11.32±3.10**
|
23.76±13.65
|
19.64±12.28
|
17.59±9.06
|
14.38±7.58
|
|
9.10±8.08
|
|
∗∗ P<0.01 represent comparisons of the amateur group and the professional group.
3.6 Comparisons of femur load during Bafa Wubu of Tai Chi and walking
As shown in Fig. 8 and Fig. 9, there was no significant difference in femur load during SKR and walking, whereas femur load is more significant during other six sets of actions than that during walking. The femur load in descending order was ELS, PPS, PB, LF, WOF, RBB, SKR, and walking. The maximum loading point was located at the greater trochanter of the femur during walking, while it shifted to the body of the femur during the seven sets of actions. Femur stress was the largest during ELS, mainly located on the outer side of the body of the femur, whereas the maximum loading point shifts to the inner side of the body of the femur during PPS, to the posterior inner-side of the body of the femur during PB, to the inner side of the body of the femur during WOF, to the neck of the femur during PB, to the posterior outer-side of the body of the femur and the neck of the femur during LF, to the inner side of the body of the femur during SKR. During the training process of Bafa Wubu, the stress constantly changes during the actions and is distributed evenly on the femur, which indicates Bafa Wubu’s capacity to stimulate femur effectively.
3.7 Verification of the lower extremity muscle strength from the AnyBody simulation
To verify the effectiveness of the AnyBody simulation data, a correlation analysis of EMG and the simulated muscle strength of the lower extremities of AnyBody was conducted. As demonstrated in Fig. 10, there is a strong correlation (r>0.7) between the simulated muscle strength and the EMG of the lower extremities, which proves that the AnyBody simulation is reliable.