Edited by: Jae Kun Shim, University of Maryland College Park, USA
Reviewed by: Hyun Gu Kang, California State University San Marcos, USA; Max J. Kurz, University of Nebraska Medical Center (UNMC), USA
*Correspondence: Tijs Delabastita
This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
Observational research suggests that in children with cerebral palsy, the altered arm swing is linked to instability during walking. Therefore, the current study investigates whether children with cerebral palsy use their arms more than typically developing children, to enhance gait stability. Evidence also suggests an influence of walking speed on gait stability. Moreover, previous research highlighted a link between walking speed and arm swing. Hence, the experiment aimed to explore differences between typically developing children and children with cerebral palsy taking into account the combined influence of restricting arm swing and increasing walking speed on gait stability. Spatiotemporal gait characteristics, trunk movement parameters and margins of stability were obtained using three dimensional gait analysis to assess gait stability of 26 children with cerebral palsy and 24 typically developing children. Four walking conditions were evaluated: (i) free arm swing and preferred walking speed; (ii) restricted arm swing and preferred walking speed; (iii) free arm swing and high walking speed; and (iv) restricted arm swing and high walking speed. Double support time and trunk acceleration variability increased more when arm swing was restricted in children with bilateral cerebral palsy compared to typically developing children and children with unilateral cerebral palsy. Trunk sway velocity increased more when walking speed was increased in children with unilateral cerebral palsy compared to children with bilateral cerebral palsy and typically developing children and in children with bilateral cerebral palsy compared to typically developing children. Trunk sway velocity increased more when both arm swing was restricted and walking speed was increased in children with bilateral cerebral palsy compared to typically developing children. It is proposed that facilitating arm swing during gait rehabilitation can improve gait stability and decrease trunk movements in children with cerebral palsy. The current results thereby partly support the suggestion that facilitating arm swing in specific situations possibly enhances safety and reduces the risk of falling in children with cerebral palsy.
The forelimbs have a clear locomotor function in quadrupedal walking. In human walking, this function most likely changed as the upper limbs do not make contact to the ground during upright walking. Irrespective of its quadrupedal neural base (Jackson,
In pathological populations, the arm swing pattern can be affected or altered during gait, which could result in changes in the function of the arm swing. Altered arm swing patterns have been reported in children with cerebral palsy. Cerebral palsy is a group of permanent disorders of the development of movement and posture, causing activity limitation, that are attributed to non-progressive disturbances that occur in the developing fetal or infant brain (Rosenbaum et al.,
While several changes of arm swing patterns have been reported in children with cerebral palsy, experimental evidence investigating the cause for these findings is still lacking. Nevertheless, such evidence should facilitate a more targeted therapeutic approach. For instance, previous correlational research suggested that altered arm swing in children with cerebral palsy plays an increased role in maintaining gait stability compared to typically developing children (Meyns et al.,
Additionally, other authors previously suggested a possible influence of walking speed on gait stability. However, the exact relationship remains unclear (Dingwell and Marin,
Finally, a strong reciprocal influence between arm swing and walking speed was previously reported in children with cerebral palsy (Meyns et al.,
Twenty-six children with cerebral palsy (age range 4–12 years) and 24 typically developing children (age range 5–12 years) were included in the study. The cerebral palsy group consisted of 11 children with unilateral cerebral palsy and 15 children with bilateral cerebral palsy, recruited from the Clinical Motion Analysis Laboratory of the U.Z. Leuven (Pellenberg). The children with cerebral palsy were only included in the study if they were diagnosed with the predominantly spastic type of cerebral palsy. Diagnosis and type of cerebral palsy were determined by a multidisciplinary team of neuropediatricians, pediatric orthopedicians, and rehabilitation physicians after neurological examination (including magnetic resonance imaging). The participants had to be able to walk without assistive devices and were only allowed to participate if they showed enough cooperation to follow the instructions concerning the walking trials. The children were excluded if they underwent Botulinum Toxin A treatment within the past 6 months or if they previously underwent lower limb surgery. The local ethical committee (Commissie Medische Ethiek KU Leuven) approved all experiments (approval number S51498). In accordance with the Declaration of Helsinki, written informed consent was obtained of the participants' parents.
Three-dimensional total-body kinematic data (100 Hz) were captured by an eight camera Vicon system (Oxford Metrics, Oxford, UK) to detect the reflective markers placed on the participant's skin. Similarly to Romkes et al. (
The marker coordinates were filtered and smoothed using Woltring's quintic spline routine with a predicted mean-squared error of 15. Further processing in Workstation (Vicon Workstation 5.2 beta 20, Oxford Metrics, Oxford, UK) and Polygon (version 3.1, Oxford Metrics, Oxford, UK) consisted of defining gait cycles and calculating spatiotemporal gait parameters. In children with cerebral palsy, the most affected side was defined as the side on which the highest median spasticity score (Modified Ashworth Scale) was obtained in the lower limb. In typically developing children, the least affected side was defined as their dominant side.
Various outcome measures were assessed to determine the children's stability during walking. In accordance with recent literature concerning stability measures in experimental situations, several spatiotemporal parameters were calculated (Bruijn et al.,
Furthermore, maximal amplitude, maximum velocity and maximum acceleration values for trunk sway and trunk rotation were calculated for all trials. The maximal amplitude was defined as the angle between the maximal value of trunk excursion on the most affected side and the maximal value of trunk excursion on the least affected side in one trial. Trunk sway was quantified in the frontal plane by calculating the angle between the axis through the C7 marker and the sacrum marker and the vertical axis. Similarly, the angle between the axis through the shoulder markers and the axis through the pelvic markers in the coronal plane was determined to evaluate trunk rotations.
In addition to the spatiotemporal parameters and the kinematic trunk data, the margin of stability was used as a measure of gait stability. The margin of stability is specifically developed as a measure of dynamic stability (Pai and Patton,
All outcome measures were calculated for three successfully recorded trials in each condition of the experiment. Both the mean values and standard deviations over these trials were retained for further analysis. To avoid misinterpretations, “variability” will be used to refer to the magnitude of the standard deviations of the parameters.
A one-way ANOVA was used to compare age, height and weight of typically developing children, children with unilateral and children with bilateral cerebral palsy. A general linear model was used to compare walking speed between subject groups in different walking speed conditions. Herein, subject group was included as a factor (between-subjects) and both arm swing condition (free arm swing or restricted arm swing) and walking speed condition (preferred walking speed or walking “as fast as possible”) were included as repeated measures factors (within-subjects). Moreover, a Mann-Whitney U Test was used to compare children with unilateral cerebral palsy and children with bilateral cerebral palsy for differences regarding the Gross Motor Function Classification Scale-levels and the Modified Ashworth Scale-grades (on the most affected side).
A general linear model was performed to determine the influence of restricting arm swing and increasing walking speed on the outcome parameters, i.e., mean values and the variability of the previously described (1) spatiotemporal parameters; (2) kinematic parameters of trunk movement; (3) margin of stability. The general linear model included subject group as a factor (between-subjects) and arm swing condition (free arm swing or restricted arm swing) and walking speed condition (preferred walking speed or walking “as fast as possible”) as repeated measures factors (within-subjects). To explore group differences regarding the influence of restricting arm swing on gait stability, the arm swing condition * subject group interactions of the performed general linear models were analyzed. Walking speed condition * subject group interactions were analyzed to explore group differences regarding the influence of increasing walking speed on gait stability. Similarly, arm swing condition * walking speed condition * subject group interactions were analyzed to explore group differences regarding the combined influence of restricting arm swing and increasing walking speed on gait stability. Following the general linear model, Tukey's Honestly Significant Difference-tests were used to perform pairwise comparisons. Moreover, Partial Eta Squared-tests were performed to compute effect sizes for all interactions revealed by the general linear models. Cohen's D-test were performed to compute effect sizes for the pairwise comparisons revealed by the Tukey's Honestly Significant Difference-test.
Statistical analyses were performed using Statistica 8.0 (StatSoft, Inc., USA). The level of significance was set at 0.05 for all tests.
Group comparisons revealed no differences regarding age and weight (Table
24 | 15 | 11 | |
Gender (M/F) | 12/12 | 11/4 | 8/3 |
GMFCS (I/II/III) | – | 8/6/1 |
7/4/0 |
Modified ashworth scale | |||
Hip flexors | 1 (0 − 2); 1 (0 − 2) | 0 (0 − 1); 1 (0 − 1+) | |
Bi-articular hip adductors | 1 (0 − 2); 1+ (0 − 2) | 0 (0 − 1); 1 (0 − 1+) | |
Mono-articular hip adductors | 1 (0 − 2); 1+ (0 − 2) | 0 (0 − 1); 0 (0 − 1.5) | |
Hamstrings | 1+ (0 − 3); 1+ (0 − 3) | 1 (0 − 1+); 1+ (1 − 2) | |
Ankle plantarflexors (measured at 0° knee flexion) | 1+ (1 − 2); 2 (0 − 3) | 0 (0 − 1+); 2 (0 − 3) | |
Ankle plantarflexors (measured at 90° knee flexion) | 1+ (0 − 2); 1+ (0 − 2) | 0 (0 − 1+); 1+ (0 − 2) | |
Overall median | 1+ (0 − 3); 1+ (0 − 3) | 0 (0 − 1+); 1 (0 − 3) | |
Age (y: years, m: months) | 9y 5m ± 2y 2m | 9y 11m ± 2y 6m | 7y 10m ± 3y 0m |
Weight (kg) | 31.72 ± 8.64 | 31.54 ± 13.36 | 23.87 ± 7.57 |
Height (m) | 1.38 ± 0.14 | 1.34 ± 0.19 | 1.22 ± 0.15 |
Statistical analysis revealed a significant walking speed condition * subject group interaction for walking speed (
“Free arm swing and preferred walking speed” | (m/s) | 1.19 ± 0.16 | 0.94 ± 0.24 | 1.10 ± 0.13 |
“Restricted arm swing and preferred walking speed” | (m/s) | 1.18 ± 0.16 | 0.83 ± 0.35 | 1.01 ± 0.13 |
“Free arm swing and high walking speed” | (m/s) | 1.93 ± 0.26 | 1.41 ± 0.41 | 1.67 ± 0.18 |
“Restricted arm swing and high walking speed” | (m/s) | 1.98 ± 0.16 | 1.35 ± 0.47 | 1.61 ± 0.16 |
Statistical analysis revealed a significant arm swing * subject group interaction for double support time (
Double support time (%) | 0.169 ± 0.011 | 0.154 ± 0.011 | 0.199 ± 0.014 | 0.233 ± 0.013 | 0.158 ± 0.016 | 0.165 ± 0.015 | * |
Step length (%) | 0.448 ± 0.009 | 0.448 ± 0.011 | 0.364 ± 0.011 | 0.354 ± 0.013 | 0.422 ± 0.013 | 0.403 ± 0.016 | |
Step width (%) | 0.084 ± 0.008 | 0.081 ± 0.012 | 0.102 ± 0.010 | 0.119 ± 0.015 | 0.080 ± 0.011 | 0.090 ± 0.017 | |
Stride length (%) | 0.904 ± 0.018 | 0.898 ± 0.022 | 0.714 ± 0.023 | 0.667 ± 0.028 | 0.854 ± 0.026 | 0.834 ± 0.032 | |
Trunk sway amplitude (°) | 5.662 ± 0.905 | 5.852 ± 0.869 | 13.717 ± 1.121 | 13.234 ± 1.076 | 7.880 ± 1.309 | 7.320 ± 1.256 | |
Trunk sway velocity (°/s) | 0.354 ± 0.055 | 0.334 ± 0.045 | 0.761 ± 0.068 | 0.700 ± 0.056 | 0.563 ± 0.080 | 0.534 ± 0.066 | |
Trunk sway acceleration (°/s2) | 0.119 ± 0.031 | 0.061 ± 0.041 | 0.130 ± 0.039 | 0.179 ± 0.051 | 0.148 ± 0.045 | 0.208 ± 0.060 | * |
Trunk rotation amplitude (°) | 22.192 ± 1.652 | 22.329 ± 1.915 | 27.199 ± 2.046 | 26.226 ± 2.371 | 26.771 ± 2.389 | 25.280 ± 2.769 | |
Trunk rotation velocity (°/s) | 1.298 ± 0.115 | 1.251 ± 0.100 | 1.649 ± 0.142 | 1.564 ± 0.124 | 1.746 ± 0.166 | 1.708 ± 0.144 | |
Trunk rotation acceleration (°/s2) | 0.433 ± 0.125 | 0.220 ± 0.065 | 0.575 ± 0.155 | 0.402 ± 0.080 | 0.562 ± 0.181 | 0.609 ± 0.094 | |
Margin of stability (m) | 0.051 ± 0.007 | 0.053 ± 0.007 | 0.074 ± 0.008 | 0.077 ± 0.009 | 0.064 ± 0.008 | 0.057 ± 0.009 |
A significant arm swing * subject group interaction was found regarding trunk sway acceleration variability (
Double support time (%) | 0.035 ± 0.009 | 0.020 ± 0.007 | 0.029 ± 0.011 | 0.045 ± 0.008 | 0.028 ± 0.012 | 0.024 ± 0.010 | |
Step length (%) | 0.023 ± 0.002 | 0.019 ± 0.002 | 0.028 ± 0.003 | 0.025 ± 0.003 | 0.027 ± 0.004 | 0.026 ± 0.003 | |
Step width (%) | 0.016 ± 0.002 | 0.015 ± 0.002 | 0.019 ± 0.003 | 0.017 ± 0.002 | 0.017 ± 0.003 | 0.022 ± 0.003 | |
Stride length (%) | 0.042 ± 0.005 | 0.035 ± 0.004 | 0.040 ± 0.006 | 0.039 ± 0.005 | 0.038 ± 0.008 | 0.045 ± 0.006 | |
Trunk sway amplitude (°) | 1.500 ± 0.178 | 1.535 ± 0.144 | 2.370 ± 0.220 | 2.555 ± 0.179 | 1.705 ± 0.237 | 1.654 ± 0.209 | |
Trunk sway velocity (°/s) | 0.083 ± 0.013 | 0.071 ± 0.012 | 0.123 ± 0.016 | 0.146 ± 0.015 | 0.122 ± 0.019 | 0.106 ± 0.017 | |
Trunk sway acceleration (°/s2) | 0.046 ± 0.016 | 0.021 ± 0.036 | 0.030 ± 0.020 | 0.111 ± 0.045 | 0.053 ± 0.023 | 0.089 ± 0.052 | * |
Trunk rotation amplitude (°) | 4.145 ± 0.534 | 4.317 ± 0.577 | 4.429 ± 0.661 | 4.964 ± 0.714 | 4.427 ± 0.772 | 5.860 ± 0.834 | |
Trunk rotation velocity (°/s) | 0.260 ± 0.070 | 0.251 ± 0.058 | 0.462 ± 0.087 | 0.379 ± 0.072 | 0.441 ± 0.101 | 0.506 ± 0.084 | |
Trunk rotation acceleration (°/s2) | 0.158 ± 0.122 | 0.071 ± 0.056 | 0.426 ± 0.152 | 0.193 ± 0.069 | 0.276 ± 0.177 | 0.353 ± 0.081 | |
Margin of stability (m) | 0.019 ± 0.005 | 0.017 ± 0.004 | 0.016 ± 0.005 | 0.018 ± 0.004 | 0.022 ± 0.005 | 0.024 ± 0.005 |
No statistically significant group differences were revealed regarding the influence of restricting arm swing on the margin of stability (Tables
A significant walking speed condition * subject group interaction was found for step length (
Double support time (%) | 0.197 ± 0.011 | 0.127 ± 0.010 | 0.248 ± 0.014 | 0.185 ± 0.013 | 0.193 ± 0.016 | 0.129 ± 0.015 | |
Step length (%) | 0.405 ± 0.010 | 0.492 ± 0.011 | 0.335 ± 0.012 | 0.382 ± 0.013 | 0.380 ± 0.014 | 0.445 ± 0.015 | * |
Step width (%) | 0.082 ± 0.013 | 0.083 ± 0.007 | 0.123 ± 0.016 | 0.098 ± 0.009 | 0.089 ± 0.018 | 0.081 ± 0.011 | |
Stride length (%) | 0.811 ± 0.020 | 0.991 ± 0.022 | 0.641 ± 0.025 | 0.741 ± 0.027 | 0.780 ± 0.030 | 0.908 ± 0.032 | * |
Trunk sway amplitude (°) | 4.870 ± 0.858 | 6.644 ± 0.943 | 12.233 ± 1.062 | 14.718 ± 1.168 | 6.223 ± 1.240 | 8.977 ± 1.364 | |
Trunk sway velocity (°/s) | 0.258 ± 0.044 | 0.430 ± 0.058 | 0.574 ± 0.055 | 0.843 ± 0.072 | 0.375 ± 0.064 | 0.723 ± 0.084 | * |
Trunk sway acceleration (°/s2) | 0.102 ± 0.032 | 0.078 ± 0.040 | 0.117 ± 0.039 | 0.192 ± 0.050 | 0.127 ± 0.046 | 0.229 ± 0.058 | * |
Trunk rotation amplitude (°) | 15.790 ± 1.507 | 28.730 ± 1.984 | 21.889 ± 1.866 | 31.535 ± 2.457 | 20.279 ± 2.179 | 31.772 ± 2.869 | |
Trunk rotation velocity (°/s) | 0.883 ± 0.093 | 1.666 ± 0.124 | 1.193 ± 0.115 | 2.019 ± 0.154 | 1.249 ± 0.134 | 2.205 ± 0.180 | |
Trunk rotation acceleration (°/s2) | 0.384 ± 0.092 | 0.268 ± 0.102 | 0.362 ± 0.113 | 0.615 ± 0.126 | 0.466 ± 0.132 | 0.705 ± 0.147 | * |
Margin of stability (m) | 0.046 ± 0.006 | 0.058 ± 0.008 | 0.067 ± 0.007 | 0.084 ± 0.010 | 0.058 ± 0.007 | 0.062 ± 0.010 |
A significant walking speed condition * subject group interaction was found for stride length (
A significant walking speed condition * subject group interaction was found for trunk sway velocity (
No significant group differences were revealed regarding the influence of increasing walking speed on the margin of stability (Tables
Double support time (%) | 0.022 ± 0.002 | 0.033 ± 0.011 | 0.028 ± 0.003 | 0.046 ± 0.013 | 0.023 ± 0.004 | 0.029 ± 0.015 | |
Step length (%) | 0.021 ± 0.003 | 0.021 ± 0.002 | 0.026 ± 0.003 | 0.026 ± 0.003 | 0.031 ± 0.004 | 0.022 ± 0.003 | |
Step width (%) | 0.015 ± 0.002 | 0.016 ± 0.002 | 0.018 ± 0.003 | 0.018 ± 0.003 | 0.018 ± 0.003 | 0.021 ± 0.003 | |
Stride length (%) | 0.036 ± 0.005 | 0.041 ± 0.005 | 0.035 ± 0.006 | 0.043 ± 0.006 | 0.051 ± 0.007 | 0.031 ± 0.008 | * |
Trunk sway amplitude (°) | 1.166 ± 0.123 | 1.869 ± 0.188 | 2.179 ± 0.152 | 2.747 ± 0.233 | 1.382 ± 0.177 | 1.978 ± 0.272 | |
Trunk sway velocity (°/s) | 0.071 ± 0.013 | 0.083 ± 0.012 | 0.118 ± 0.016 | 0.151 ± 0.015 | 0.091 ± 0.018 | 0.137 ± 0.018 | |
Trunk sway acceleration (°/s2) | 0.045 ± 0.022 | 0.023 ± 0.030 | 0.069 ± 0.028 | 0.071 ± 0.037 | 0.053 ± 0.032 | 0.089 ± 0.043 | |
Trunk rotation amplitude (°) | 3.164 ± 0.440 | 5.298 ± 0.664 | 3.999 ± 0.545 | 5.394 ± 0.822 | 4.259 ± 0.636 | 6.028 ± 0.960 | |
Trunk rotation velocity (°/s) | 0.225 ± 0.066 | 0.286 ± 0.054 | 0.370 ± 0.082 | 0.470 ± 0.067 | 0.439 ± 0.096 | 0.508 ± 0.078 | |
Trunk rotation acceleration (°/s2) | 0.155 ± 0.067 | 0.074 ± 0.109 | 0.232 ± 0.083 | 0.387 ± 0.135 | 0.273 ± 0.097 | 0.356 ± 0.158 | |
Margin of stability (m) | 0.012 ± 0.004 | 0.023 ± 0.006 | 0.015 ± 0.004 | 0.019 ± 0.006 | 0.020 ± 0.004 | 0.025 ± 0.006 |
No significant group differences were found regarding the spatiotemporal parameters.
A significant arm swing condition * walking speed condition * subject group interaction was observed for trunk sway velocity (
Double support time (%) | 0.207 ± 0.010 | 0.186 ± 0.013 | 0.131 ± 0.014 | 0.123 ± 0.012 | 0.231 ± 0.013 | 0.264 ± 0.016 | 0.167 ± 0.017 | 0.202 ± 0.014 | 0.190 ± 0.015 | 0.195 ± 0.019 | 0.125 ± 0.020 | 0.134 ± 0.017 | |
Step length (%) | 0.404 ± 0.009 | 0.406 ± 0.012 | 0.493 ± 0.011 | 0.491 ± 0.011 | 0.341 ± 0.011 | 0.328 ± 0.015 | 0.386 ± 0.013 | 0.379 ± 0.014 | 0.388 ± 0.013 | 0.372 ± 0.018 | 0.455 ± 0.015 | 0.434 ± 0.014 | |
Step width (%) | 0.083 ± 0.006 | 0.081 ± 0.013 | 0.084 ± 0.005 | 0.081 ± 0.006 | 0.107 ± 0.008 | 0.138 ± 0.017 | 0.098 ± 0.007 | 0.099 ± 0.007 | 0.088 ± 0.009 | 0.090 ± 0.020 | 0.073 ± 0.008 | 0.089 ± 0.008 | |
Stride length (%) | 0.810 ± 0.018 | 0.812 ± 0.025 | 0.999 ± 0.022 | 0.984 ± 0.023 | 0.678 ± 0.022 | 0.604 ± 0.031 | 0.750 ± 0.027 | 0.731 ± 0.028 | 0.795 ± 0.026 | 0.765 ± 0.036 | 0.913 ± 0.032 | 0.903 ± 0.033 | * |
Trunk sway amplitude (°) | 5.108 ± 0.939 | 4.632 ± 0.811 | 6.216 ± 0.957 | 7.072 ± 0.999 | 12.818 ± 1.162 | 11.649 ± 1.005 | 14.615 ± 1.186 | 14.820 ± 1.237 | 6.366 ± 1.357 | 6.080 ± 1.173 | 9.394 ± 1.384 | 8.560 ± 1.445 | |
Trunk sway velocity (°/s) | 0.306 ± 0.053 | 0.209 ± 0.039 | 0.402 ± 0.063 | 0.459 ± 0.056 | 0.607 ± 0.066 | 0.540 ± 0.048 | 0.825 ± 0.078 | 0.860 ± 0.070 | 0.363 ± 0.077 | 0.386 ± 0.056 | 0.763 ± 0.091 | 0.682 ± 0.082 | * |
Trunk sway acceleration (°/s2) | 0.171 ± 0.030 | 0.033 ± 0.025 | 0.067 ± 0.024 | 0.089 ± 0.036 | 0.092 ± 0.037 | 0.143 ± 0.031 | 0.168 ± 0.030 | 0.216 ± 0.044 | 0.079 ± 0.043 | 0.175 ± 0.037 | 0.218 ± 0.034 | 0.240 ± 0.052 | * |
Trunk rotation amplitude (°) | 17.464 ± 1.167 | 14.116 ± 1.137 | 26.919 ± 1.451 | 30.541 ± 1.949 | 23.761 ± 1.445 | 20.017 ± 1.408 | 30.637 ± 1.797 | 32.434 ± 2.413 | 21.968 ± 1.687 | 18.591 ± 1.645 | 31.574 ± 2.098 | 31.970 ± 2.818 | |
Trunk rotation velocity (°/s) | 1.134 ± 0.124 | 0.631 ± 0.090 | 1.461 ± 0.133 | 1.871 ± 0.150 | 1.237 ± 0.153 | 1.150 ± 0.112 | 2.061 ± 0.165 | 1.978 ± 0.186 | 1.244 ± 0.179 | 1.255 ± 0.131 | 2.249 ± 0.193 | 2.161 ± 0.217 | * |
Trunk rotation acceleration (°/s2) | 0.658 ± 0.131 | 0.111 ± 0.082 | 0.207 ± 0.155 | 0.329 ± 0.069 | 0.371 ± 0.162 | 0.353 ± 0.102 | 0.779 ± 0.192 | 0.451 ± 0.086 | 0.373 ± 0.189 | 0.558 ± 0.119 | 0.750 ± 0.224 | 0.660 ± 0.100 | * |
Margin of stability (m) | 0.045 ± 0.004 | 0.047 ± 0.005 | 0.057 ± 0.006 | 0.058 ± 0.007 | 0.064 ± 0.005 | 0.069 ± 0.006 | 0.083 ± 0.008 | 0.085 ± 0.008 | 0.062 ± 0.005 | 0.055 ± 0.006 | 0.066 ± 0.008 | 0.059 ± 0.008 |
Statistical analysis also revealed a significant arm swing condition * walking speed condition * subject group interaction for trunk rotation velocity (
Analysis of the arm swing * walking speed * group interactions of the margin of stability revealed no significant differences (Table
Double support time (%) | 0.022 ± 0.002 | 0.022 ± 0.003 | 0.049 ± 0.017 | 0.018 ± 0.014 | 0.026 ± 0.003 | 0.030 ± 0.004 | 0.031 ± 0.021 | 0.060 ± 0.017 | 0.022 ± 0.004 | 0.023 ± 0.005 | 0.033 ± 0.024 | 0.024 ± 0.020 | |
Step length (%) | 0.022 ± 0.004 | 0.020 ± 0.003 | 0.024 ± 0.003 | 0.019 ± 0.003 | 0.028 ± 0.005 | 0.025 ± 0.004 | 0.028 ± 0.004 | 0.024 ± 0.003 | 0.035 ± 0.005 | 0.027 ± 0.005 | 0.020 ± 0.005 | 0.025 ± 0.004 | |
Step width (%) | 0.014 ± 0.002 | 0.016 ± 0.002 | 0.018 ± 0.002 | 0.014 ± 0.002 | 0.019 ± 0.002 | 0.017 ± 0.003 | 0.019 ± 0.003 | 0.016 ± 0.002 | 0.012 ± 0.003 | 0.024 ± 0.003 | 0.022 ± 0.003 | 0.020 ± 0.003 | |
Stride length (%) | 0.036 ± 0.005 | 0.036 ± 0.004 | 0.048 ± 0.006 | 0.034 ± 0.005 | 0.036 ± 0.006 | 0.035 ± 0.006 | 0.043 ± 0.007 | 0.043 ± 0.006 | 0.049 ± 0.007 | 0.054 ± 0.006 | 0.026 ± 0.008 | 0.037 ± 0.007 | |
Trunk sway amplitude (°) | 1.123 ± 0.167 | 1.209 ± 0.150 | 1.877 ± 0.251 | 1.862 ± 0.240 | 2.015 ± 0.207 | 2.342 ± 0.186 | 2.726 ± 0.310 | 2.768 ± 0.297 | 1.428 ± 0.242 | 1.336 ± 0.217 | 1.982 ± 0.362 | 1.973 ± 0.346 | |
Trunk sway velocity (°/s) | 0.080 ± 0.015 | 0.062 ± 0.016 | 0.086 ± 0.017 | 0.080 ± 0.015 | 0.101 ± 0.018 | 0.136 ± 0.020 | 0.146 ± 0.021 | 0.156 ± 0.019 | 0.092 ± 0.021 | 0.091 ± 0.024 | 0.151 ± 0.024 | 0.122 ± 0.022 | |
Trunk sway acceleration (°/s2) | 0.070 ± 0.014 | 0.019 ± 0.026 | 0.022 ± 0.014 | 0.024 ± 0.032 | 0.022 ± 0.018 | 0.116 ± 0.032 | 0.037 ± 0.017 | 0.105 ± 0.040 | 0.022 ± 0.021 | 0.084 ± 0.037 | 0.083 ± 0.020 | 0.095 ± 0.046 | |
Trunk rotation amplitude (°) | 3.178 ± 0.338 | 3.150 ± 0.454 | 5.112 ± 0.602 | 5.484 ± 0.610 | 3.524 ± 0.418 | 4.473 ± 0.562 | 5.334 ± 0.746 | 5.455 ± 0.755 | 3.599 ± 0.489 | 4.919 ± 0.656 | 5.254 ± 0.871 | 6.801 ± 0.882 | |
Trunk rotation velocity (°/s) | 0.278 ± 0.082 | 0.172 ± 0.096 | 0.241 ± 0.089 | 0.330 ± 0.046 | 0.349 ± 0.102 | 0.392 ± 0.119 | 0.576 ± 0.110 | 0.365 ± 0.057 | 0.385 ± 0.119 | 0.493 ± 0.139 | 0.496 ± 0.129 | 0.519 ± 0.067 | |
Trunk rotation acceleration (°/s2) | 0.257 ± 0.082 | 0.052 ± 0.081 | 0.058 ± 0.183 | 0.089 ± 0.054 | 0.247 ± 0.102 | 0.218 ± 0.100 | 0.605 ± 0.226 | 0.168 ± 0.067 | 0.143 ± 0.119 | 0.402 ± 0.117 | 0.409 ± 0.264 | 0.303 ± 0.078 | |
Margin of stability (m) | 0.012 ± 0.003 | 0.013 ± 0.004 | 0.026 ± 0.006 | 0.021 ± 0.004 | 0.015 ± 0.003 | 0.016 ± 0.004 | 0.018 ± 0.006 | 0.020 ± 0.004 | 0.020 ± 0.003 | 0.021 ± 0.005 | 0.023 ± 0.007 | 0.026 ± 0.005 |
In the current study, the influence of restricting arm swing and increasing walking speed in typically developing children and children with both unilateral and bilateral cerebral palsy was compared to gain insight on the stabilizing role of arm swing during walking. First, it was hypothesized that gait stability would decrease more in children with cerebral palsy compared to typically developing children when arm swing is restricted. It was also expected that gait stability would decrease more in children with bilateral cerebral palsy compared to children with unilateral cerebral palsy when arm swing is restricted. Second, it was hypothesized that gait stability would decrease more in children with cerebral palsy compared to typically developing children when walking speed is increased. It was also expected that gait stability would decrease more in children with bilateral cerebral palsy compared to children with unilateral cerebral palsy when walking speed is increased. Finally, it was hypothesized that gait stability would decrease more in children with cerebral palsy compared to typically developing children when both arm swing is restricted and walking speed is increased. It was also expected that gait stability would decrease more in children with bilateral cerebral palsy compared to children with unilateral cerebral palsy when both arm swing is restricted and walking speed is increased. Additionally, it was expected that the influence of restricting arm swing combined with increasing walking speed would be larger compared to the isolated influence of these tasks.
Previous research suggested that altered arm postures in children with cerebral palsy were related to gait instability (Meyns et al.,
Double support time increased more in children with bilateral cerebral palsy compared to typically developing children and children with unilateral cerebral palsy when arm swing was restricted. Children with bilateral cerebral palsy may have tried to enhance stability of walking by minimizing the impact of an instable single support phase (Kim and Son,
The larger increase in trunk sway acceleration variability in children with bilateral cerebral palsy also suggests an increase in gait instability when arm swing is restricted. Measures of kinematic variability have been extensively used to quantify gait stability (Bruijn et al.,
Increased trunk sway acceleration variability in children with bilateral cerebral palsy could also be explained by trunk control deficits in children with cerebral palsy (Heyrman et al.,
Next to possible trunk control deficits, altered angular momentum in children with cerebral palsy could also partly explain the observed group differences regarding trunk kinematics. Previous research indicated that arm swing movements compensated for the angular momentum (around a vertical axis) disruptions during walking by the involved leg in children with unilateral cerebral palsy (Bruijn et al.,
It is remarkable that no differences were detected regarding the influence of restricting arm swing on gait stability for children with unilateral cerebral palsy compared to typically developing children. It seems that restricting arm swing did not sufficiently challenge children with unilateral cerebral palsy to increase gait instability more compared to typically developing children. Therefore, it is assumed that the role of arm swing in gait stability is smaller in children with unilateral cerebral palsy compared to children with bilateral cerebral palsy.
Furthermore, no changes in margins of stability and step width were found when arm swing was restricted (nor when walking speed was increased; see below). This possibly suggests that gait stability is very mildly affected. On the other hand, it is possible that restricting arm swing affects gait stability in a specific direction. Previous research indicated that children with unilateral cerebral palsy show gait instability in both the medio-lateral and the antero-posterior direction (Bruijn et al.,
In conclusion, children with bilateral cerebral palsy showed larger increases in double support time and trunk sway acceleration variability compared to typically developing children and children with unilateral cerebral palsy. As hypothesized, these findings suggest that arm swing has a stabilizing role during gait in children with bilateral cerebral palsy. Trunk control deficits and trunk compensations for disrupted angular momentum are also suggested to influence gait instability in children with bilateral cerebral palsy (although to a smaller degree). Furthermore, the hypothesis that restricting arm swing would decrease gait stability more in children with bilateral cerebral palsy compared to children with unilateral cerebral palsy seems to be confirmed.
Since we aimed to evaluate the combined effect of increasing walking speed and restricting arm swing, the isolated influence of walking speed on the measures of stability is described first.
Typically developing children increased step length and stride length more compared to children with bilateral cerebral palsy when walking speed was increased. Children with cerebral palsy face muscle shortening, muscle contractures and/or spasticity. Since spasticity is dependent of muscle lengthening velocity, this could influence step length more when increasing walking speed. Children with unilateral cerebral palsy increased step length more compared to children with bilateral cerebral palsy when walking speed was increased. This difference is likely to be explained by the lower spasticity values in children with unilateral cerebral palsy and bilateral involvement in children with bilateral cerebral palsy (in contrast to unilateral involvement in children with unilateral cerebral palsy).
The reported group differences regarding the increase in trunk sway velocity when walking speed was increased could also be explained by compensations for differences regarding the increase in step length and stride length. However, step (stride) length increased more in children with unilateral cerebral palsy compared to children with bilateral cerebral palsy. If step (stride) length primarily caused the reported group differences regarding trunk sway velocity, one would expect a smaller increase in trunk sway velocity in children with bilateral cerebral palsy compared to children with unilateral cerebral palsy. Clearly, this is not supported by the results. Moreover, previous research indicated that altered trunk movements in children with cerebral palsy are not likely to be compensations due to lower limb impairments (Heyrman et al.,
Furthermore, increased trunk sway acceleration variability in children with bilateral cerebral palsy could also be explained by trunk control deficits in children with cerebral palsy (Heyrman et al.,
Additionally, the reported group differences regarding the increase in trunk sway velocity when walking speed was increased could be explained by differences regarding the angular momentum around the vertical axis. Both children with bilateral cerebral palsy and children with unilateral cerebral palsy increased trunk sway velocity more when walking speed was increased. Previous research already indicated that the angular momentum around the vertical of the unaffected arm and leg in children with unilateral cerebral palsy were higher compared to typically developing children (Bruijn et al.,
In conclusion, children with cerebral palsy showed larger increases regarding trunk sway velocity when walking speed was increased compared to typically developing children. Furthermore, children with unilateral cerebral palsy increased trunk sway velocity more compared to children with bilateral cerebral palsy when walking speed was increased. It is proposed that the group differences regarding the increase in trunk sway velocity when walking speed was increased may be considered as an indication for trunk compensational movements for angular momentum disruptions. Trunk control deficits, trunk compensations for muscle spasticity and impaired step length are also suggested to influence trunk sway velocity in children with bilateral cerebral palsy (although to a smaller degree). In contrast to the research hypothesis, gait stability did not decrease more in children with cerebral palsy compared to typically developing children when walking speed was increased.
An important group difference regarding the combined influence of restricting arm swing and increasing walking speed was found (similar to the isolated influence of increasing walking speed). A stronger increase in trunk sway velocity has been observed in children with bilateral cerebral palsy compared to typically developing children when subjects walking with restricted arm swing were asked to increase walking speed. This possibly suggests that increasing walking speed combined with restricting arm swing decreases gait stability more in children with bilateral cerebral palsy compared to typically developing children. However, these findings should certainly be interpreted with care because other factors (trunk control deficits, altered angular momentum and compensations for lower limb impairments) may interfere with the combined influence of arm swing and walking speed on gait stability (as mentioned above).
Furthermore, typically developing children showed a specific reaction when arm swing was restricted at preferred walking speed (and not at increased walking speed). Both trunk sway and trunk rotation decreased compared to walking with the arms free at the preferred walking speed. This “en bloc” strategy was not found in either group of children with cerebral palsy. Therefore, it is assumed that the trunk is required to move in children with cerebral palsy when arm swing is restricted.
In conclusion, children with bilateral cerebral palsy increased trunk sway velocity more compared to typically developing children when subjects walking with restricted arm swing were asked to increase walking speed. Overall, evidence is insufficient to conclude that restricting arm swing combined with increasing walking speed induced larger group differences regarding gait stability compared to their isolated effects. Thereby, the experimental data could not confirm the postulated research hypotheses regarding the influence of both restricted arm swing and increased walking speed on gait stability. However, the results showed that children with cerebral palsy adopted different responses to arm swing restriction compared to typically developing children regarding trunk kinematics.
When interpreting the results of the current study, certain methodological issues should be taken into account. It is possible that the study sample consisting of 24 typically developing children and 26 children with cerebral palsy was too small and/or heterogeneous. This could have caused some marginally non-significant changes that were reported. Additionally, more children with bilateral cerebral palsy had a GMFCS level II than children with unilateral cerebral palsy. These differences certainly need to be taken into account when comparing these two groups. Most of the subjects included in the group of children with cerebral palsy had a GMFCS level I. This mildly involved population could have caused an underestimation of the actual differences between typically developing children and children with cerebral palsy.
Second, Bruijn et al. (
Finally, trunk movements were not described using joint angles. However, elevation angles were used (i.e., the angle between segments projected in one plane). As such, a simplified kinematic method was used. In previous research, this approach was found to be adequate to detect meaningful changes in the kinematics during walking in this population, in agreement with literature using joint angles (Meyns et al.,
In conclusion, restricting arm swing influenced gait stability more in children with bilateral cerebral palsy compared to both typically developing children and children with unilateral cerebral palsy. As such, the current study is the first to support experimentally that arm swing compensates (at least partly) for affected stability in children with bilateral cerebral palsy. Results were less clear for children with unilateral cerebral palsy. In contrast to the research hypotheses, increasing walking speed did not affect gait stability more in children with cerebral palsy compared to typically developing children (nor in children with bilateral cerebral palsy compared to children with unilateral cerebral palsy). However, the current results indicate that increasing walking speed increased trunk compensations for altered angular momentum around a vertical axis more in children with cerebral palsy compared to typically developing children. The effects were larger in children with unilateral cerebral palsy compared to children with bilateral cerebral palsy because more trunk movements were already observed in children with bilateral cerebral palsy at preferred walking speed. In contrast to the research hypotheses, restricting arm swing combined with increasing walking speed did not induce larger group differences regarding gait stability compared to their isolated effects. Overall, it is proposed that facilitating arm swing during gait rehabilitation can improve gait stability and decrease trunk movements in children with cerebral palsy. The current results partly support the suggestion that facilitating arm swing in specific situations possibly enhances safety and reduce the risk of falling in children with cerebral palsy. Other authors already suggested a similar approach for other pathologies (e.g., stroke and spinal cord injury) in previous research (Stephenson et al.,
PM and KD conceived and designed the experiment. PM performed the experiments. PM and TD together analyzed the data. Furthermore, TD, PM, and KD wrote the paper. The writing process and the data analysis were supervised by PM and KD.
This project was supported by grants from the “bijzonder onderzoeksfonds” KU Leuven (OT/08/034 & PDMK/12/180) and from the Research Foundation Flanders (FWO grant G.0901.11; “Krediet aan Navorser” grant 1503915N). PM is supported by the European Commission (Horizon 2020) as a Marie Skłodowska-Curie fellow (proposal 660458). The funding agencies had no role in the present study.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
We thank the physical therapists of the Laboratory of Clinical Movement Analysis of the University Hospital Leuven (U.Z. Leuven). Their aid and experience was of great importance for this research.