- Email: [email protected]
THE RELATIONSHIP BETWEEN CENTER OF PRESSURE AND CENTER OF MASS IN GAIT IN THE CHILDREN WITH CEREBRAL PALSY AND NORMAL DEVELOPMENT
Gait and Balance 1 – Balance Control in Pathological Gait. 14:15, Room 101CD,
Presentation 0519
S123
THE RELATIONSHIP BETWEEN CENTER OF PRESSURE AND CENTER OF MASS IN GAIT IN THE CHILDREN WITH CEREBRAL PALSY AND NORMAL DEVELOPMENT B-J Hsue12, F Miller1, F-C Su2, J Henley1, C Church1 dePont Hospital for Children, Wilmington DE, USA; 2 Institute of Biomedical Engineering, National Cheng Kung University, Taiwan email: [email protected] 1
INTRODUCTION In ambulation, the body is in a more optimal and stable position when the center of mass (COM) is closer to the point of support or center of pressure (COP). However, it may not be sensitive enough to pinpoint the postural control and balance problem in cerebral palsy (CP) by just looking at the spatial relationship between COM and COP since the whole-body COM is actually projected forward along a moving base of support, therefore, the temporal components of COM and COP which represents the moving of the body and weight shifting, respectively, certainly play an important role in dynamic stability. So, besides examining the spatial relationship between the vertical projection of COM and COP, the purpose of this study was to investigate the velocity (Vel) and acceleration (Acc) of the COM and COP in antero-posterior (AP) and medio-lateral (ML) directions during level walking in the children with CP and compare the data with those of the children with typical motor development (TD), and to determine what the most appropriate strategies are in identify dynamic balance in CP.
and ML directions are shown in Table 1. In Hemi group, the average proportion of SL of the affected side is significantly shorter than the other two groups, and than the normal side. The COM and COP displacement of the Di group was significantly lower in AP direction and higher in ML direction than the TD group, but peak Acc were higher than the TD group. Besides higher Acc value, the mean profiles of the COP Acc in ML (Figure 1) and AP (not shown) directions shows Di group reaches the peak at the end of 1st SL rather than in the early (Hemi) or middle (TD) of DS, which may indicate that the subjects in Di group generate force and speed for the opposite leg to step forward. On the other hand, it may suggest the risk of instability in SL. Unlike TD group, Di and Hemi groups demonstrate latency between the peak COM and COP Vel and Acc that indicates an inefficient muscle work for balance control in walking. The divergence between COM and COP is smallest in TD group throughout the phases, and largest in Di group which may result from the exaggerated movements in walking. The distance between COM and COP in ML direction 0.1
METHODS Subjects included 4 independently ambulatory hemiplegic (aged 10.7±2.8 y/o) and 6 diplegic (aged 10.3±3.8 y/o) CP children, and 5 children with TD in the same age range. All subjects in diplegic group (Di) had mild to moderate toe walking at one or both sides, and the subjects in hemiplegic group (Hemi) had moderate to severe toe walking at one side. The participants walked barefoot with comfortable speeds, and the COM and COP parameters from 3 trials with most similar speed were used for analysis. An eight-camera Eagle Motion Analysis System (60 Hz) (Motion Analysis Corp, CA) was used to capture the 3-dimensional trajectory data of the whole body markers. An eleven segment model with the anthropometric data was used to calculate the COM. Ground reactions forces were collected by two AMTI force plates (960 Hz) (Advanced Mechanical Tech Inc, MA) and used to compute COP. The velocity and acceleration of COM and COP were acquired by calculating their first and second derivatives. One cycle included a full single limb (SL) stand of one leg, double support and SL stand of the other leg. The temporal data, as well as the displacement, Vel and Acc of COM and COP, were normalized to 100 data points for comparison. The peak value of parameters was compared utilizing one-way ANOVA at the 0.05 level of significance. RESULTS AND DISCUSSION The three phase proportion and peak-to-peak displacement, maximal velocity and acceleration of COM and COP in AP
Hemi Di TD
DS
0.05
2nd SL
0
1st SL
-0.05 -0.1
10
20
30
40
50
60
70
80
90
100
80
90
100
90
100
COP and COM acceleration in ML direction 0.06
DS
1st SL
0.04
2nd SL
0.02 0 -0.02 -0.04
0
10
20
30
40
50
60
70
60
70
0.02
0.01
0
1st SL
-0.01
-0.02
0
10
20
DS
30
40
2nd SL
50
80
Figure 1: The distance between COM and COP (top), and Acc of COP (middle) and COM (bottom) in ML direction; the solid, dot and dash lines separate the stance phase for TD, Di, and Hemi groups, respectively. CONCLUSIONS Each group in this pilot study demonstrates its own identical pattern in COP parameters. Disagreeing with Massaad’s finding [1], COM parameters are different in Di and Hemi groups. More variations in COM parameters may suggest that the CP children use different strategies for balance. REFERENCES 1 Massaad F et al. Develop Med Child Neurol, 49 674-680, 2004
Table 1: Mean percentage of three gait phases, and mean peak value of COM and COP of three groups. Group
Hemi Di TD 1
Time Proportion (%) 1st SL1 DS 2nd SL 37.9±8.8* 42.3±3.5 44.6±1.4
COM and COP in AP direction Displacement (m) Vel (m/sec) Acc (m/sec2)
COM and COP in ML direction Displacement (m) Vel (m/sec) Acc (cm/sec2)
18.6±8.9 43.6±0.5 0.82±0.17 0.54±0.10 1.22±0.20 7.04±2.78 0.04±0.01 0.24±0.09 0.04±0.01 0.15±0.02 0.13±0.03 2.22±1.24 0.03±0.01 0.08±0.05 17.3±2.9 40.4±1.8* 0.72±0.08* 0.47*±0.05 1.14±0.10* 6.97±1.00 0.04±0.02 0.25±0.04 0.04±0.01 0.17±0.07 0.13±0.04 2.50±1.21* 0.03±0.01 0.09±0.04 10.9±1.7* 44.5±0.8 0.86±0.11 0.59±0.06 1.29±0.16 6.78±1.97 0.02±0.00* 0.21*±0.08 0.03±0.01 0.10±0.01* 0.10±0.04 1.41*±0.46 0.01±0.00* 0.05±0.02*
The 1st SL phase for Hemi group is the SL of affected side; * p < 0.05 as compared with the other two groups
XXI ISB Congress, Podium Sessions, Monday 2 July 2007
Journal of Biomechanics 40(S2)
Presentation 0519
S123
THE RELATIONSHIP BETWEEN CENTER OF PRESSURE AND CENTER OF MASS IN GAIT IN THE CHILDREN WITH CEREBRAL PALSY AND NORMAL DEVELOPMENT B-J Hsue12, F Miller1, F-C Su2, J Henley1, C Church1 dePont Hospital for Children, Wilmington DE, USA; 2 Institute of Biomedical Engineering, National Cheng Kung University, Taiwan email: [email protected] 1
INTRODUCTION In ambulation, the body is in a more optimal and stable position when the center of mass (COM) is closer to the point of support or center of pressure (COP). However, it may not be sensitive enough to pinpoint the postural control and balance problem in cerebral palsy (CP) by just looking at the spatial relationship between COM and COP since the whole-body COM is actually projected forward along a moving base of support, therefore, the temporal components of COM and COP which represents the moving of the body and weight shifting, respectively, certainly play an important role in dynamic stability. So, besides examining the spatial relationship between the vertical projection of COM and COP, the purpose of this study was to investigate the velocity (Vel) and acceleration (Acc) of the COM and COP in antero-posterior (AP) and medio-lateral (ML) directions during level walking in the children with CP and compare the data with those of the children with typical motor development (TD), and to determine what the most appropriate strategies are in identify dynamic balance in CP.
and ML directions are shown in Table 1. In Hemi group, the average proportion of SL of the affected side is significantly shorter than the other two groups, and than the normal side. The COM and COP displacement of the Di group was significantly lower in AP direction and higher in ML direction than the TD group, but peak Acc were higher than the TD group. Besides higher Acc value, the mean profiles of the COP Acc in ML (Figure 1) and AP (not shown) directions shows Di group reaches the peak at the end of 1st SL rather than in the early (Hemi) or middle (TD) of DS, which may indicate that the subjects in Di group generate force and speed for the opposite leg to step forward. On the other hand, it may suggest the risk of instability in SL. Unlike TD group, Di and Hemi groups demonstrate latency between the peak COM and COP Vel and Acc that indicates an inefficient muscle work for balance control in walking. The divergence between COM and COP is smallest in TD group throughout the phases, and largest in Di group which may result from the exaggerated movements in walking. The distance between COM and COP in ML direction 0.1
METHODS Subjects included 4 independently ambulatory hemiplegic (aged 10.7±2.8 y/o) and 6 diplegic (aged 10.3±3.8 y/o) CP children, and 5 children with TD in the same age range. All subjects in diplegic group (Di) had mild to moderate toe walking at one or both sides, and the subjects in hemiplegic group (Hemi) had moderate to severe toe walking at one side. The participants walked barefoot with comfortable speeds, and the COM and COP parameters from 3 trials with most similar speed were used for analysis. An eight-camera Eagle Motion Analysis System (60 Hz) (Motion Analysis Corp, CA) was used to capture the 3-dimensional trajectory data of the whole body markers. An eleven segment model with the anthropometric data was used to calculate the COM. Ground reactions forces were collected by two AMTI force plates (960 Hz) (Advanced Mechanical Tech Inc, MA) and used to compute COP. The velocity and acceleration of COM and COP were acquired by calculating their first and second derivatives. One cycle included a full single limb (SL) stand of one leg, double support and SL stand of the other leg. The temporal data, as well as the displacement, Vel and Acc of COM and COP, were normalized to 100 data points for comparison. The peak value of parameters was compared utilizing one-way ANOVA at the 0.05 level of significance. RESULTS AND DISCUSSION The three phase proportion and peak-to-peak displacement, maximal velocity and acceleration of COM and COP in AP
Hemi Di TD
DS
0.05
2nd SL
0
1st SL
-0.05 -0.1
10
20
30
40
50
60
70
80
90
100
80
90
100
90
100
COP and COM acceleration in ML direction 0.06
DS
1st SL
0.04
2nd SL
0.02 0 -0.02 -0.04
0
10
20
30
40
50
60
70
60
70
0.02
0.01
0
1st SL
-0.01
-0.02
0
10
20
DS
30
40
2nd SL
50
80
Figure 1: The distance between COM and COP (top), and Acc of COP (middle) and COM (bottom) in ML direction; the solid, dot and dash lines separate the stance phase for TD, Di, and Hemi groups, respectively. CONCLUSIONS Each group in this pilot study demonstrates its own identical pattern in COP parameters. Disagreeing with Massaad’s finding [1], COM parameters are different in Di and Hemi groups. More variations in COM parameters may suggest that the CP children use different strategies for balance. REFERENCES 1 Massaad F et al. Develop Med Child Neurol, 49 674-680, 2004
Table 1: Mean percentage of three gait phases, and mean peak value of COM and COP of three groups. Group
Hemi Di TD 1
Time Proportion (%) 1st SL1 DS 2nd SL 37.9±8.8* 42.3±3.5 44.6±1.4
COM and COP in AP direction Displacement (m) Vel (m/sec) Acc (m/sec2)
COM and COP in ML direction Displacement (m) Vel (m/sec) Acc (cm/sec2)
18.6±8.9 43.6±0.5 0.82±0.17 0.54±0.10 1.22±0.20 7.04±2.78 0.04±0.01 0.24±0.09 0.04±0.01 0.15±0.02 0.13±0.03 2.22±1.24 0.03±0.01 0.08±0.05 17.3±2.9 40.4±1.8* 0.72±0.08* 0.47*±0.05 1.14±0.10* 6.97±1.00 0.04±0.02 0.25±0.04 0.04±0.01 0.17±0.07 0.13±0.04 2.50±1.21* 0.03±0.01 0.09±0.04 10.9±1.7* 44.5±0.8 0.86±0.11 0.59±0.06 1.29±0.16 6.78±1.97 0.02±0.00* 0.21*±0.08 0.03±0.01 0.10±0.01* 0.10±0.04 1.41*±0.46 0.01±0.00* 0.05±0.02*
The 1st SL phase for Hemi group is the SL of affected side; * p < 0.05 as compared with the other two groups
XXI ISB Congress, Podium Sessions, Monday 2 July 2007
Journal of Biomechanics 40(S2)