Oxygen Cost, Walking Speed, and Perceived Exertion In Children with Cerebral Palsy When Walking with Anterior and Posterior Walkers,
by E. Mattsson and C. Andersson, Developmental Medicine and Child Neurology, 1997;39:671–676.
Children with cerebral palsy (CP) often require assistive devices for ambulation and stability. Walkers, either the anterior or posterior type, are often prescribed for the child. The posterior walker fosters a more upright postural alignment than the anterior walker, which promotes forward flexion. Using any assistive device requires more oxygen per kilogram of body weight and per meter traveled compared with walking in healthy individuals. Learning to walk with an assistive device can initially cause gait to be slower, more exhausting, and frustrating for the child. Parent and child must be convinced that the initial discomforts of the new walker will likely decrease with time. To investigate whether the difficulties with a new walker do decrease with continued use, studies of children familiar with both types of walkers have been conducted. The purpose of this article was to determine if a difference in walking speed, energy cost, and perceived exertion exists when comparing ambulation with anterior and posterior walkers in children with CP who were familiar with both devices. The authors hope that the results of this study could influence assistive device recommendations.
Participants in the study were children who had: 1) a diagnosis of spastic CP, 2) the ability to follow instructions, 3) the ability to walk with anterior and posterior walkers for five minutes, and 4) practiced with anterior and posterior walkers for the past six months. A total of 10 children participated (seven with spastic diplegia and three with ataxic diplegia). The age ranged from eight to 17 years with a mean of 11 years. Surgical interventions such as hamstring release, Strayer procedure, and adductor tenotomy had been performed on six participants. All children used assistive devices for ambulation. Two children wore ankle-foot orthoses.
The test was conducted at the children’s schools in Stockholm. At the beginning of the study, spasticity in all the extremities was assessed in supine with the modified Ashworth scale. The participants walked at a self-determined pace on level ground in a circle (circumference 70 meter) for at least four minutes. They used their own walkers during the first trial in which no data were collected. Next, each child was assigned randomly to complete the test with either the posterior or anterior walker. For the second part, the child used the other walker. Heart rate, walking speed, and oxygen consumption were recorded while the children walked. A telemetric device was used to measure heart rate. The child had to achieve a steady pace—defined as a heart rate change of no more than two beats in one minute. A speedometer mounted on a cart that the test-leader pushed behind the child recorded walking speed. Oxygen cost was measured by argon-diluted method using a mixing box attached to a backpack carried by the child. A facemask captured the expired air and the flexible tubing transported the air to the mixing box.
Oxygen cost was derived from the results of mass spectrometer analysis. After each test, the participants rated their perceive exertion both in their own words and by pointing to one of five face pictures depicting different levels of exertion (1 = least exertion to 5 = greatest exertion).
No differences were detected between participants who used the anterior or posterior walker first. The spasticity scores on the modified Ashworth scale ranged from one to two in the upper extremities and from one plus to two in the lower extremities. Average resting heart rate was 96 bpm (range 76–112 bpm). The average heart rate for children walking with both the anterior and posterior walkers was 147 bpm. The average walking speeds were 27.2 meters/min and 28.8 meters/min for anterior and posterior walkers, respectively. One child walked at the same pace with both walkers; whereas seven children walked quicker and two children walked slower with the posterior walker. There was no significant difference between the two walkers in oxygen cost both per minute and per meter. Values of oxygen cost when walking with the anterior and posterior walkers were significantly correlated (r = 0.81, p < 0.01). The median perceived exertion score using the anterior walker was 3.5 (range one to five). Three children rated walking with the anterior walker as very easy and four reported it as very hard. The verbal ratings were “very easy,” “easy,” “rather easy,” “all right,” “hard,” and “very hard.” For walking with the posterior walker, five children rated the task as very easy and two participants rated it as rather hard. The median was two (range one to four). Seven of the children preferred the posterior walker, whereas three preferred the anterior walker. One participant like both walkers, but favored the anterior walker.
The purpose of the study was to compare the physiological effects of walking with anterior and posterior walkers in children with CP. To limit the influence of learning how to ambulate with each device, only children familiar with both walkers were used in the study. The authors acknowledged that this criterion reduced the sample size to 10 possible candidates. The participants’ responses to the walker preference question suggest that they, in fact, were familiar with both walkers. The resting heart rates and walking speeds found in this study corresponded with the literature. The exercise heart rate found in this study was much higher than other studies with children with CP. The authors noted that differences in age, height, and spasticity might account for variability. The children with CP in this study used a comparable amount of oxygen per kilogram body weight as compared with children without disabilities. However, when comparing oxygen cost per meter, children with CP had a much higher oxygen cost than children who were healthy. To maintain equivalent oxygen consumption with children who were healthy, CP children walked at a slower pace. Spontaneous report of perceived exertion was used because of the large variability in participants’ ages, experiences, and opinions of physically difficult tasks. The spontaneous report and the five-point scale of perceived exertion provided corresponding results.
Spasticity was measured using the modified Ashworth scale in supine, but not during walking. The authors acknowledged the possibility of altering spasticity levels when changing from supine to walking, the experimental testing position. Thus, two children may have the same spasticity score in supine, but not while walking.
The results of this study suggest that walking with an anterior walker or posterior walker had comparable physiological effects based on average heart rates, walking speeds, oxygen cost, and perceived exertion of the 10 children with CP. Because the results suggest that anterior and posterior walkers have similar physiological costs, the question remains as to whether the posterior walker can promote favorable neuromuscular development with its more vertical spinal alignment. Also, additional studies are necessary to investigate the adjustment time to a new ambulatory device and the body’s response during this period.
Limitations and Implications
The authors presented a thorough literature review to substantiate their protocol and sample selection. Comparison of the oxygen consumption of ambulation with and without assistive devices in healthy people illustrated the higher physical exertion levels required when walking with a device. The authors explained the potential benefits of using the posterior walker compared with the anterior walker. The posterior walker could contribute to the development and maintenance of a vertical spinal alignment—an underlying impetus for the study. The difference between children who have CP and those who are healthy was established in the article’s introduction, thus comparing the results to children who are healthy in the discussion seemed irrelevant. The purpose of the study was to compare the physiological effects during ambulation with anterior and posterior walkers.
The study was limited by the small sample size, the effects of body position on spasticity, and the large variability in upper extremity spasticity. More statistical power could be achieved with a larger, more diverse sample. Measures of spasticity can change in different body positions; therefore, a more direct assessment of spasticity during walking, although difficult to assess, would have enhanced the validity of the results. In addition, the procedure section did not report how much time elapsed before a steady state was achieved. A few minutes difference could generate enough fatigue to influence the results since ambulation with an assistive device has high cardiac demands for a child with CP. On the other hand, a more functional test would be to increase the duration of the steady pace to five to 10 minutes, the time needed to walk a few blocks. A study with more participants with the same qualifications and a longer and well-defined testing duration may influence the recommendation for either the anterior or posterior walker for children with CP in the future.