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Effects of Intensity of Treadmill Training on Developmental Outcomes and Stepping in Infants With Down Syndrome: A Randomized Trial

DA Ulrich, PhD, is Professor, Department of Kinesiology, and Director, Center for Motor Behavior and Pediatric Disabilities, University of Michigan, 401 Washtenaw Ave, Ann Arbor, MI 48109-2214 (USA)
MC Lloyd, MA, CW Tiernan, MS, and JE Looper, PT, MSPT, are doctoral candidates in the Department of Kinesiology, University of Michigan, and are associated with the Center for Motor Behavior and Pediatric Disabilities
RM Angulo-Barroso, PhD, is Associate Professor, Department of Kinesiology, University of Michigan, and is associated with the Center for Motor Behavior and Pediatric Disabilities

Address all correspondence to Dr Ulrich at: ulrichd{at}umich.edu

Submitted May 8, 2007; Accepted July 26, 2007

	Abstract

 
Background and Purpose: Infants with Down syndrome (DS) are consistently late walkers. The purpose of this investigation was to test the effects of individualized, progressively more intense treadmill training on developmental outcomes in infants with DS.

Subjects: Thirty infants born with DS were randomly assigned to receive lower-intensity, generalized treadmill training or higher-intensity, individualized training implemented by their parents in their homes.

Methods: Research staff members monitored implementation of training, physical growth, and onset of motor milestones of all infants on a monthly basis.

Results: Infants in the higher-intensity, individualized training group increased their stepping more dramatically over the course of training. Infants in the higher-intensity training group attained most of the motor milestones at an earlier mean age.

Discussion and Conclusion: Treadmill training of infants with DS is an excellent supplement to regularly scheduled physical therapy intervention for the purpose of reducing the delay in the onset of walking.

	Introduction

Top Abstract Introduction Method Results Discussion Conclusion References

 
Down syndrome (DS) is one of the few disabilities that carries with it the certainty of delays in all of the developmental domains.¹ In the United States, DS occurs approximately 1.36 times in every 1,000 live births.² Down syndrome is a common cause of cognitive deficits in childhood³ and results in significant delays in the onset of motor skills, including qualitative differences in movement patterns, compared with the typical development in children without DS.^4,5

Considerable variability exists among infants and children with DS with regard to the degree of disability and the specific features affected. Greater joint range of motion, presumably attributable to ligamentous laxity,⁶ delayed development of postural reactions and myelination,⁷ low muscle tone,⁸ and congenital heart defects⁹ all contribute to delayed motor skills. For example, children with DS tend to sit without support by 11 months, pull up to a standing position at about 17 months, and walk 3 independent steps at an average age of 24 to 26 months.¹⁰ Palisano and colleagues¹¹ found that 73% of the children with DS whom they observed longitudinally were able to stand by 24 months of age and that 40% could walk by 24 months. In contrast, the average ages of onset of standing alone and onset of walking in infants with typical development are 11 and 12 months, respectively.¹²

Locomotor experience represents a critical life transition for young children and promotes the advancement of perception, spatial cognition, and social and motor skills.¹³ Researchers have demonstrated that, in infants with typical development, experience with locomotion contributes to the onset of a broad array of psychological skills, such as wariness of heights, recognizing that objects hidden from view may still exist, shifting from self-centered to landmark-based spatial coding strategies, distance perception, and acquiring aspects of social referencing.^13,14 These results suggested that infants learn more about the world around them as they become able to locomote independently and can actively explore their environment rather than passively observing it.

On the basis of motor theory¹⁵ and principles of neurophysiology,¹⁶ we propose that functionally relevant practice should accelerate progress in the acquisition of specific motor skills. Hallett stated that "intensive, focused physical therapy should help restore motor function, and evidence shows that the earlier and more intensive the therapy, the better the outcome."^{17(p xix)} The target population for that statement was patients with stroke, but on the basis of the principles of neuroplasticity, this argument also applies equally to pediatric habilitation. An important goal of early motor therapy is to facilitate continual exploration and selection of the movement patterns needed for functional movement behavior,^16,18 and the earlier this process begins, the better.¹⁹ Priority should be placed on functionally significant tasks, such as locomotion. The major challenge for pediatric therapists and parents is finding innovative ways to promote exploration and practice of locomotor skills, such as crawling and walking, before the skills actually begin to emerge.

Ulrich et al²⁰ demonstrated that, by 11 months of age, infants with DS can produce coordinated alternating steps when supported under their arms on a small motorized treadmill (Fig. 1), and stepping increases over developmental time.²¹ With these systematic observations, they hypothesized that the treadmill holds promise as a potential early intervention. In a 4-year randomized clinical trial, regularly scheduled pediatric physical therapy intervention was supplemented with treadmill training implemented by parents in their homes.⁵ The results demonstrated that the structured treadmill training facilitated a significantly earlier onset of independent walking than did regularly scheduled physical therapy intervention only. The infants who received the supplemental treadmill training walked, on average, at a corrected age of 20.0 months (SD=2.9 months); for the infants in the control group, the corresponding value was 24.3 months (SD=6.6 months). The treadmill training conditions used by the parents were considered to be low-intensity training (8 minutes per day for 5 days per week).

View larger version (104K): [in this window] [in a new window]   Figure 1. Example of an infant with Down syndrome being trained on a small motorized treadmill by her mother. (For a video clip, visit Supplemental Video)

The publication of treadmill training studies carried out with a variety of populations has increased over the last decade.^24–26 Belt speeds have ranged from 0.15 m/s to 0.26 m/s for infants and from 0.23 m/s to 0.34 m/s for children. The best results appear to be associated with individualizing belt speeds on the basis of the stepping performance of a child.^25,26 Duration was individualized in studies involving older children, and the result was increased performance.²⁶ Individualizing training protocols appears to be a strategy worth testing in infants with DS.

Given that the randomized intervention study of Ulrich et al⁵ was the first of its type, the optimal level of intensity of treadmill training for infants with DS is not known. Our goal in this study was to test the effects of more intense, individualized training. Specifically, we wanted to determine the effects of this protocol on step frequency over time and the onset of functional locomotor skill development and to compare this protocol with the low-intensity, generalized training used in the earlier research.⁵

	Method

Top Abstract Introduction Method Results Discussion Conclusion References

 
Participants

Thirty-six infants with DS were recruited to participate in the study via parent support groups located in lower Michigan. Neither race nor sex precluded infants from being enrolled in the study. Exclusion criteria were the presence of a seizure disorder, noncorrectable vision problems, and any other medical conditions that would severely limit a child's participation in the treadmill intervention. All parents signed informed consent forms and provided supplemental information about their child and family background. The criterion for starting the treadmill intervention was the ability to take a minimum of 6 supported steps in a given minute on the treadmill. For most infants, the intervention began at 10 months of age. Infants were randomly assigned to the higher-intensity, individualized treadmill training (HI) group or the lower-intensity, generalized treadmill training (LG) group. Our final sample included 30 infants (16 in the HI group and 14 in the LG group). Data for 6 infants who were initially recruited were excluded from the analyses because their parents routinely did not adhere to the protocol (1 infant in the LG group and 3 infants in the HI group) or because of emerging medical conditions (2 infants). Table 1 provides a summary of data on participant characteristics prior to the intervention. There were no significant group differences in the characteristics of the participants.

The treadmill training protocol for the LG group included 8 minutes per day for 5 days per week at a belt speed of 0.15 m/s throughout the intervention. In the HI group, as infants progressed in their stepping performance, we added ankle weights, increased belt speed, and increased daily duration in an effort to maximize the stepping response. We viewed the legs, during the swing phase, as pendulums and predicted that the addition of weights to the ankles once the infants were stepping would have a positive effect by increasing the forward motion of the leg at toe-off.²⁷ We also expected that the addition of weights would increase afferent sensory feedback and facilitate the development of the neuromuscular system, a critical subsystem needed for stepping.

As a result of observing the infants in our earlier treadmill training study over developmental time,⁵ we concluded that the infants were capable of more than 8 minutes of training per day and at a gradually increasing belt speed. These conditions were initiated once the infants displayed the ability to take 10 steps per minute and increased when the infants were able to take 20, 30, and 40 steps per minute. The decision on when to increase the training conditions was based on the videotaped performances during the biweekly follow-up sessions conducted by our research team (Tab. 2). The amount of ankle weight added was individualized as a percentage (50%, 75%, 100%, and 125%) of a child's calf mass.²⁷ If a child's performance regressed below the required stepping frequency (ie, 10, 20, 30, or 40 steps per minute) once the training conditions were increased, then we delayed a change in the protocol until the stepping frequency was maintained at the minimum frequency required.

Data Reduction and Analysis

Videotapes of infants' treadmill performances during staff member visits were coded for the frequency of alternating steps over the five 1-minute trials. Next, the average number of alternating steps per minute was determined. Finally, an average number of alternating steps per minute over a 2-month span was calculated and used for statistical analyses. For a "step" to be counted, the foot had to initiate toe off behind the trunk and pass the midline of the body in the sagittal plane. An "alternating step" was defined as a step in leg 1 followed by a step in leg 2; the swing phase of leg 2 had to occur during the stance phase of leg 1.

In order to determine whether the protocol provided to the HI group was more beneficial than the protocol provided to the LG group in terms of increasing the number of alternating steps taken over time, we conducted 2 analyses. First, a t test was performed for the number of alternating steps taken during the first visit to assess whether differences existed between the groups at study entry. Second, we used a 2 (group) x 5 (time) analysis of variance with repeated measures across time and with frequency of alternating steps as the dependent variable. Given that infants in each group walked at different ages, the numbers of actual data collection points for each infant varied. For this analysis, we used bimonthly average step frequencies. A total of 5 time points was chosen because that was the minimum number of bimonthly sessions common to all participants. For children who walked later and had more than 5 bimonthly sessions throughout the study, the 5 visits most equally spaced over the total time from study entry to walking onset were selected for analysis (session quintiles), thereby allowing us to capture stepping performance throughout the entire span of participation in the study.

To test the hypothesis that the HI group would acquire motor milestones at a younger age than the LG group, we initially conducted a test of homogeneity of variances in the age of onset of each motor milestone. All of the variances were smaller for the HI group, but only 4 of the 8 values were statistically significant. The Mann-Whitney U test²⁹ was used to test for significant group differences in the age of onset of each milestone. As a follow-up to the nonparametric procedures, we calculated effect size statistics (standardized difference between group means, expressed as standard deviations). We also conducted a principal components analysis (PCA), in which we treated the group of 8 motor milestones as a unidimensional locomotor construct.

	Results

Top Abstract Introduction Method Results Discussion Conclusion References

 
All parents kept training logs throughout the study and were asked to record the following: the days on which training occurred, the number of minutes practiced per day, reasons for days of training missed, and a statement about the child's performance while engaged in the treadmill training. From the parents’ logs, we calculated the average protocols that were carried out for the HI and LG groups (Tab. 3). The results demonstrated that, on average, the HI group gradually increased training conditions throughout the study and the LG group maintained a constant set of conditions, as we planned. However, some variance from the intended protocols occurred (Tabs. 2 and 3). Parents’ logs suggested that this variance was attributable to a variety of circumstances, such as family vacations, child and caregiver illnesses, busy personal schedules, and regression in treadmill stepping frequency for some infants when the protocol conditions increased. Unlike the situation in our earlier treadmill training study,⁵ the parents in the present study were not as successful in their efforts to make up for days of training missed or unexpected perturbations in their daily schedules.

View larger version (11K): [in this window] [in a new window]   Figure 2. Alternating steps taken by infants who received higher-intensity, individualized treadmill training (high) or lower-intensity, generalized treadmill training (low). Data are reported as mean (SE indicated by error bars).

	Discussion

Top Abstract Introduction Method Results Discussion Conclusion References

 
For infants and young children with DS, early interventions are critical to promoting positive developmental outcomes in both the motor and the cognitive domains.^5,8 Often there is little or no empirical evidence to indicate the level of effectiveness of interventions or the intensity at which they should be implemented. Treadmill training has been shown to be effective in decreasing the delay in the onset of independent walking in infants with DS.⁵ The results of the present study reinforced the effectiveness of treadmill training for facilitating walking onset compared with the average age of walking onset in infants who have DS but who receive traditional physical therapy alone.^5,11 In the present study, we attempted to improve the effectiveness of the treadmill training protocol for infants with DS by manipulating the training conditions to gradually increase intensity.

Our results demonstrated that participants in both the HI and the LG groups showed increases in the frequency of alternating steps over time. However, a significant group x time interaction with regard to alternating step frequency suggested that the patterns of change across the training period were different for the HI and LG groups (Fig. 2). The 2 groups were similar during the initial treadmill training primarily because the intensities of training were similar. We propose that the addition of weights to the ankles of participants in the HI group had an initial effect of depressing alternating step frequency until sufficient strength to manipulate the added mass was acquired. This process took longer than originally conceived. Eventually, infants in the HI group benefited because their increased leg strength resulted in significantly more stepping during the last 2 quintiles. In the LG group, increases in step frequency occurred gradually and consistently over the 5 quintiles.

The data from the present study replicate and expand on the results of our earlier treadmill training study⁵ indicating that the infants who received the experimental treadmill training walked, on average, at a corrected age of 20 months. In the present study, the infants in the LG group walked independently, on average, at 21.3 months—earlier than the infants who received physical therapy intervention but no treadmill training in the earlier study and who walked at an average age of 24.3 months.⁵ In the present study, the infants in the HI group walked independently at an average age of 19.2 months—earlier than the infants in previous reports.^5,11 Palisano and colleagues¹¹ reported that in a sample of 121 infants who had DS and who were receiving early intervention services, only 40% walked independently by 2 years of age. In the present study, 94% of the children in the HI group and 71% of those in the LG group walked before 2 years of age. The ability to walk independently at least 3 to 4 months earlier than would be typically expected is important both clinically and functionally in the life of a child with a disability and his or her parents.

In the present early intervention study, several infants displayed adequate leg strength and postural control needed to walk and were able to walk well with assistance. Unfortunately, they refused to let go of their parent's fingertips and walk independently for an additional 3 to 4 months. Similar results were observed in our earlier treadmill training study.⁵ It is our hypothesis that these infants displayed a higher level of instability because of ligamentous laxity around their ankle joints and that this instability affected their independent walking behavior. Future research is needed to test this hypothesis and to design and test modifications to the treadmill training procedures, such as the use of orthoses to reduce instability around the feet and ankles once an infant assumes a standing posture.

Several other motor milestones were monitored throughout the present study (Tab. 4). No statistically significant differences were found between the HI and the LG groups, with the exception of the following items: moves forward using prewalking methods and raises self to standing position. Given that the milestone of moving forward using prewalking methods was acquired quite early in the intervention period, it is not likely that it was attributable to the HI protocol because at that point, the HI and LG protocols were very similar. The effect sizes, however, showed that HI did make a meaningful contribution to most of the motor milestones. The results of the PCA, in which the 8 motor milestones were combined into a unidimensional locomotor construct, supported this view.

Early intervention theory suggests that higher-intensity interventions may produce greater positive outcomes^19,22; however, there is little empirical evidence to support this position. We recognize that most therapists define intensity in terms of frequency of therapy sessions and total minutes per session. Our goals in the present study were to explore gradual increases in treadmill training conditions in anticipation of significantly increasing the amount of treadmill stepping practice occurring before a child began to walk independently and to evaluate whether increased practice speeds hastened the onset of motor milestones. We are currently testing whether the HI procedures provide other benefits, such as those related to overall physical activity (stamina) or quality of walking gait.

Several factors could have contributed to the limited statistically significant differences in the onset of motor milestones. Table 3 shows that the treadmill training protocol for the HI group was not implemented exactly as intended by some families, although it was gradually more intense than the protocol for the LG group. Several factors could have influenced the outcomes. Parenting in the early years of a child's life is hectic and stressful; this situation is magnified when a child in the family has a disability that requires a considerable amount of attention.³¹ The time commitment required for the HI intervention appeared not to be overly burdensome; however, 6 to 8 minutes per day for 5 days per week may be the saturation point for busy parents. Finally, it also is possible that too many variables were manipulated in this exploratory attempt to gradually increase the intensity of treadmill training for infants with DS. Manipulating belt speed, daily duration, and the amount of weight attached to the ankles on the basis of individual infant performance might be too complex. To reduce complexity for parents and researchers, we advise that each condition be manipulated separately. Our lack of significant group differences could mean that the LG protocol was intense enough to meaningfully increase the frequency of stepping and push the infants to achieve motor milestones earlier than they would have without the treadmill intervention. In considering which procedures to manipulate in the future in an effort to increase intensity, gradually increasing belt speed as an infant increases the frequency of stepping should be the first condition selected. As an infant begins to take more steps on the treadmill, belt speed is associated with more stepping, assuming that the speed is not too fast.

	Conclusion

Top Abstract Introduction Method Results Discussion Conclusion References

 
The results of the present study support the evidence produced in our earlier treadmill training study involving infants with DS.⁵ Low-intensity treadmill training used as a supplement to regular physical therapy intervention for infants with DS resulted in an earlier onset of walking and other locomotor milestones compared with the findings for infants who had DS but who received physical therapy intervention only. Our efforts to explore and test procedures to gradually increase the intensity of treadmill training resulted in greater increases in the frequencies of alternating steps for participants in the HI group than for those in the LG group and meaningful differences in the age of onset of most locomotor milestones. The HI procedures used in the present study appeared to be more challenging for parents to implement consistently. Important parts of the treadmill training procedures are providing parents with feedback on their implementation of the intervention and answering their questions. Parents of participants in both the HI and the LG groups consistently claimed that they liked the structure provided by the treadmill training intervention program because they knew exactly what to do, how to do it, and for how long each day.

On the basis of the accumulation of evidence supporting the use of the treadmill as a supplement to physical therapy intervention for infants with DS, we advocate that hospitals and clinics consider purchasing appropriate treadmills and begin to rent them to parents on a monthly basis. Each infant-sized treadmill built for the present study cost about $1,200.

	Footnotes

 
Dr Ulrich provided concept/idea/research design, writing, data collection, fund procurement, facilities/equipment, and institutional liaisons. Ms Lloyd, Mr Tiernan, and Ms Looper provided writing and data collection and analysis. Dr Angulo-Barroso provided concept/idea/research design, data collection and analysis, fund procurement, and facilities/equipment. The authors thank the families and infants who participated in this research along with the Families Exploring Down Syndrome parent organization and the Down Syndrome Association of Western Michigan for assisting in the recruitment of infants.

This study was reviewed and approved by the University of Michigan Health Sciences Institutional Review Board.

This work was funded by a research grant from the US Office of Special Education and Rehabilitative Services (H324C010067), a US Office of Special Education Programs Leadership Training Grant (H325D020028), and the Steelcase Foundation in Michigan.

Preliminary data were presented as a poster delivered at the III STEP Symposium on Translating Evidence Into Practice: Linking Movement Science and Intervention; July 15–21, 2005; Salt Lake City, Utah; and as an Invited Keynote Address at the International Symposium of Adapted Physical Activity; July 5–9, 2005; Verona, Italy.

^* Carlin's Creations, 27366 Oak St, Sturgis, MI 49091.

	References

Top Abstract Introduction Method Results Discussion Conclusion References

 

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This Article Abstract Full Text (PDF) Supplemental Video All Versions of this Article: ptj.20070139v1 88/1/114    most recent Submit a response Alert me when this article is cited Alert me when Rapid Responses are posted Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Ulrich, D. A Articles by Angulo-Barroso, R. M Search for Related Content PubMed PubMed Citation Articles by Ulrich, D. A Articles by Angulo-Barroso, R. M Related Collections Adaptive/Assistive Devices Gait and Locomotion Training Outcomes Measurement Down Syndrome Randomized Controlled Trials Social Bookmarking                      What's this?