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Effects of Various Treadmill Interventions on the Development of Joint Kinematics in Infants With Down Syndrome

Jianhua Wu, Julia Looper, Dale A. Ulrich, Rosa M. Angulo-Barroso
DOI: 10.2522/ptj.20090281 Published 1 September 2010
Jianhua Wu
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Julia Looper
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Dale A. Ulrich
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Rosa M. Angulo-Barroso
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Abstract

Background Infants with Down syndrome (DS) have delayed walking and produce less-coordinated walking patterns.

Objective The aim of this study was to investigate whether 2 treadmill interventions would have different influences on the development of joint kinematic patterns in infants with DS.

Design Thirty infants with DS were randomly assigned to a lower-intensity, generalized (LG) treadmill training group (LG group) or a higher-intensity, individualized (HI) treadmill training group (HI group) and trained until walking onset. Twenty-six participants (13 in each group) completed a 1-year gait follow-up assessment.

Methods During the gait follow-up assessment, reflective markers were placed bilaterally on the participants to measure the kinematic patterns of the hip, knee, and ankle joints. Both the timing and the magnitude of peak extension and flexion at the hip, knee, and ankle joints, as well as peak adduction and abduction at the hip joint, in the 2 groups were compared.

Results Both the LG group and the HI group showed significantly advanced development of joint kinematics at the gait follow-up. In the HI group, peak ankle plantar flexion occurred at or before toe-off, and the duration of the forward thigh swing after toe-off increased.

Limitations Joint kinematics in the lower extremities were evaluated in this study. It would be interesting to investigate the effect of treadmill interventions on kinematic patterns in the trunk and arm movement.

Conclusions The timing of peak ankle plantar flexion (before toe-off) in the HI group implies further benefits from the HI intervention; that is, the HI group may use mechanical energy transfer better at the end of stance and may show decreased hip muscle forces and moments during walking. It was concluded that the HI intervention can accelerate the development of joint kinematic patterns in infants with DS within 1 year after walking onset.

Independent walking is a major milestone that infants with typical development (TD) achieve at about 1 year of age. Infants with TD show significantly increased walking speed and step length and decreased step width within 6 months after walking onset.1 The rapid development of joint kinematic patterns also is observed. Infants with TD display an out-of-phase pattern of coordination between the left and right legs at the onset of walking2 and produce coordinated movement between the thigh and the shank at 3 months after walking onset.3 Furthermore, infants with TD develop kinematic patterns at the hip, knee, and ankle joints rapidly within 6 months after walking onset, and progression is slower thereafter.4,5 For instance, at the hip joint, infants with TD show significantly increased extension and decreased flexion in the sagittal plane and increased adduction and decreased abduction in the frontal plane within 6 months after walking onset.6 However, infants with about 6 months of walking experience produce less extension and adduction at the hip joint and less extension and greater flexion at the knee joint than do adults who are healthy,7 but they produce joint kinematic patterns similar to those of 7-year-old children.8 The results of all of these studies have indicate1–7 that the first 6 months after walking onset is an important period in which new walkers rapidly develop walking patterns.

Understanding the developmental sequences of independent walking is important for both infants with TD and infants with developmental disabilities. Behavioral scientists and health care professionals rely to a great extent on such knowledge to design and implement effective physical interventions for children with disabilities, such as Down syndrome (DS), to advance their motor development. Down syndrome is a common genetic disease that significantly delays the onset of independent walking9,10 and results in less-advanced walking patterns.11–13 Infants with DS produce significantly slower walking speeds, shorter stride lengths, and wider step widths than do their peers who are healthy within 6 months after walking onset.14,15 The development of joint kinematic patterns in infants with DS also lags behind that in their peers who are healthy; infants with DS produce greater variability in shank segmental angle than do their peers who are healthy within 6 months after walking onset.14 Therefore, it can be concluded that infants with DS develop less-sophisticated walking patterns (both spatiotemporal and joint kinematic) than do infants with TD. However, no data have yet been provided to demonstrate whether physical interventions would improve the development of joint kinematic patterns in infants with DS.

Recent studies have demonstrated that treadmill interventions can be effective for infants with DS; a lower-intensity, generalized (LG) training protocol can advance walking onset in infants with DS by 3.5 months,10 and a higher-intensity, individualized (HI) training protocol can advance walking onset by 5 months.16 Infants who had DS and who received an HI treadmill intervention walked faster and produced longer stride lengths and narrower step widths than did those who received an LG treadmill intervention within 1 year after walking onset.17,18 Furthermore, the infants who received an HI treadmill intervention displayed more-rapid development in controlling step length and width variability11 and in using an adaptive strategy while negotiating an obstacle.19 All of these results suggest that the HI treadmill intervention should have a greater long-term impact on the development of both unobstructed and adaptive walking patterns than the LG treadmill intervention.

The question to be addressed in this study was whether the HI training protocol elicits better long-term development of joint kinematics (ie, adultlike timing and magnitude) in infants with DS. We examined the development of joint kinematic patterns during a 1-year span after walking onset in infants who had DS and who received either an LG treadmill intervention or an HI treadmill intervention. We hypothesized that infants who had DS and who received an HI treadmill intervention would produce more-advanced joint kinematic patterns than would those who received an LG treadmill intervention during a 1-year span after walking onset.

Method

Participants

The recruitment and characteristics of the study participants were reported by Ulrich et al.16 Figure 1 shows a flow diagram of the participants' progress during the study. In brief, 36 infants with DS were recruited from parent support groups located in lower Michigan. Infants were not precluded from the study because of race or sex. Exclusion criteria included the presence of a seizure disorder, noncorrectable vision problems, and any other medical conditions that would severely limit an infant's participation in treadmill interventions. Sample size was calculated on the basis of a previous study10 to provide 80% power at an alpha level of .05 for difference in age at walking onset. Ten percent more participants were recruited because of possible dropouts.

Figure 1.
Figure 1.

Flow diagram of participant progress through the study. Reasons for “discontinued intervention” included nonadherence to the protocol (n=4) and emerging medical conditions (n=2). Reasons for “lost to gait follow-up” included family circumstances (n=2) and emerging medical conditions (n=2). The LG group received lower-intensity, generalized treadmill training, and the HI group received higher-intensity, individualized treadmill training.

All of the participants entered the study when they could produce 6 steps per minute while being supported upright on a treadmill. Participants were randomly assigned to an LG treadmill training group (LG group) or an HI treadmill training group (HI group). Six participants (4 in the LG group and 2 in the HI group) were not adherent to the training protocol and did not complete the treadmill training. Thus, 14 participants in the LG group (5 boys and 9 girls) and 16 participants in the HI group (12 boys and 4 girls) completed the treadmill interventions. Chronological age, corrected for infants who were born more than 2 weeks before the due date, was 10.0 months (SD=1.9 months) at entry across the LG and HI groups. No significant differences were found at entry between the 2 groups in corrected chronological age, Bayley Scale of Infant Development20 raw motor scores, and anthropometric measures, such as height, weight, thigh and shank length, and thigh and shank circumference (all P values >.10). All of the participants received early intervention services and any other activities that were prescribed by their health care providers. The parents of all of the infants gave written informed consent before the infants entered the study.

Treadmill Interventions

Small, motorized, custom-designed treadmills* were provided to the families for the treadmill interventions. Parents were trained to hold their child upright on the treadmill and appropriately administer training in their homes. The details of the intended and actual LG and HI training protocols were described by Ulrich et al.16 In the LG group, the actual training was 6 minutes per day, 5 days per week, at a belt speed of 0.18 m/s throughout the training. In the HI group, participants trained 5 days per week, and the training protocol was individualized on the basis of the participant's stepping performance on the treadmill. Three training components (daily training duration, belt speed, and ankle weight) were manipulated simultaneously throughout the HI training (Tab. 1). The amount of ankle weight was proportional to the participant's estimated calf mass.21 Our research staff visited all of the participants every 2 weeks throughout the training to monitor adherence to training, record 5 minutes of treadmill stepping, take anthropometric measures, and make adjustments for the HI training protocol when appropriate. Treadmill training was terminated when the participant was able to walk 3 steps independently on the floor, our operational definition for walking onset.

View this table:
Table 1.

Mean Values for Actual Implementation of the Higher-Intensity, Individualized Training Protocola

Chronological ages at walking onset were 21.4 months (SD=4.7 months) for the LG group and 19.2 months (SD=2.8 months) for the HI group. This difference yielded a medium effect size (Cohen d=.56) in favor of the HI group.16

Gait Follow-up

A 1-year gait follow-up assessment was conducted after the treadmill interventions to investigate the long-term effects of the interventions on the development of gait patterns in infants with DS. Of 30 participants who completed the treadmill interventions, 1 in the LG group and 3 in the HI group could not complete the gait follow-up assessment because of family issues or emerging medical conditions. Thus, 26 participants visited our laboratory 4 times for gait data collection (13 in the LG group [4 boys and 9 girls] and 13 in the HI group [10 boys and 3 girls]). Seven visits by 5 participants were missing because the participants had prolonged illnesses or family issues.

The first visit for gait data collection (gait visit) was scheduled immediately after parents reported to us that their child could walk 8 to 10 steps independently at home. The second, third, and fourth gait visits were scheduled at 3, 6, and 12 months, respectively, after the first gait visit. No significant difference was found between the 2 groups in walking experience (ie, the duration from walking onset to the date of a gait visit). The mean (SD) months of walking experience across both groups were 3.0 (1.1), 6.4 (1.1), 9.4 (0.9), and 15.3 (0.9) at visits 1, 2, 3, and 4, respectively.

A 6-camera Peak Motus motion analysis system† was used to record the positions of reflective markers at a sampling rate of 60 Hz. A viewing space of 2.95 × 1.7 × 1.3 m was calibrated with a fixed calibration frame before data collection. Two cameras mounted on the ceiling were placed in the front and the back of the walkway. Two cameras mounted on tripods were placed at each side of the walkway. Participants wore only a diaper during data collection to facilitate the placement and visibility of the reflective markers. Reflective markers were placed bilaterally on the temporomandibular joint, acromion process, lateral epicondyle of the humerus, greater trochanter, lateral epicondyle of the femur, lateral malleolus, and second metatarsal head. Participants walked across the walkway toward their parents at their self-selected speeds. Data from an average of 4 unobstructed walking trials were collected at each gait visit. Some of the data collected at these gait visits were presented in another article,17 which reported the development of spatiotemporal parameters (such as walking speed, step length, and step width) and foot rotation asymmetry. The focus of the present study was the development of joint kinematics during the gait follow-up period.

Data Reduction and Analysis

Reflective markers were manually identified and filtered with a second-order Butterworth filter at a cutoff frequency of 6 Hz by use of Peak Motus software version 8.4.† The angles of the hip, knee, and ankle joints were calculated and exported from the Peak Motus software. We examined the extension and flexion of the hip, knee, and ankle joints in the sagittal plane and the adduction and abduction of the hip joint in the frontal plane. Joint angles were defined between the segment of interest and its anatomical position. For instance, knee extension or flexion was defined as an angle between the shank and the extension of the thigh, hip extension or flexion was defined as an angle between the thigh and the vertical line in the sagittal plane, and hip adduction or abduction was defined as an angle between the thigh and the vertical line in the frontal plane. Joint flexion and adduction had positive values, and joint extension and abduction had negative values. Because no significant difference was found between the left and the right sides, only the data from the right side were used for the subsequent analysis.

A custom-written Matlab program‡ was used to normalize each gait cycle to 100% and then to fit the raw joint data at each gait cycle with a cubic spline function to 101 equally spaced data points. Next, another custom-written Matlab program, which had interactive windows, was used to manually determine peak extension and flexion or peak adduction and abduction at each normalized gait cycle for each joint. Figure 2 shows the representative trajectories of the hip, knee, and ankle joints at a normalized gait cycle. Peak extension was defined as the transition from extension to flexion, and peak flexion was defined as the transition from flexion to extension. Peak adduction and peak abduction were similarly defined. We examined both the timing and the magnitude of peak joint angles. Table 2 shows the raw timing of peak joint angles (as a percentage of the gait cycle). Because major gait events are markedly related to the timing of toe-off, the timing of peak joint angles was calculated with respect to toe-off. That is, the timing of peak extension and flexion or adduction and abduction was defined as the raw timing of the peak joint angle minus the timing of toe-off. Negative timing values indicated that the peak joint angle occurred before toe-off, and positive timing values indicated that the peak joint angle occurred after toe-off.

Figure 2.
Figure 2.

Representative trajectories of hip and knee flexion and extension, ankle dorsiflexion and plantar flexion, and hip adduction and abduction during a normalized gait cycle. Joint flexion (dorsiflexion) and adduction had positive values, and joint extension (plantar flexion) and abduction had negative values. The vertical lines denote the occurrence of toe-off (ie, separating the stance phase from the swing phase). The open circles denote peak extension (plantar flexion) at the hip, knee, and ankle joints as well as peak abduction at the hip joint. The closed circles denote peak flexion (dorsiflexion) at the hip, knee, and ankle joints, as well as peak adduction at the hip joint. The timing of peak flexion and extension and peak adduction and abduction at each joint is reported as a percentage of the gait cycle with respect to toe-off (ie, the raw timing of peak joint angle minus the timing of toe-off). For example, the timing of toe-off, the raw timing of peak hip extension, and the raw timing of peak hip flexion in this figure occurred at 68%, 54%, and 89% of the gait cycle, respectively. With the timing defined in this study, peak hip extension occurred at −14% of the gait cycle (before toe-off), and peak hip flexion occurred at 21% of the gait cycle (after toe-off).

View this table:
Table 2.

Means and Standard Deviations for Raw Timing of Toe-off (as a Percentage of the Gait Cycle) and Peak Ankle, Hip, and Knee Joint Angles

A series of 2-way (2 group × 4 visit) analyses of variance with repeated measures on visit were conducted with SAS statistical software.§ Dependent variables included the timing and magnitude of peak extension and flexion at the hip, knee, and ankle joints and the timing and magnitude of peak adduction and abduction at the hip joint. Post hoc pair-wise comparisons with Bonferroni adjustments were conducted when appropriate. Statistical significance was set at P<.05.

Role of the Funding Source

This study was supported by a grant from the US Office of Special Education and Rehabilitative Services (H324C010067) and a grant awarded by the March of Dimes Birth Defects Foundation to Dr Ulrich and Dr Angulo-Barroso. The funding sources played no role in the design, conduct, or reporting of this study. The content of this publication is solely the view of the authors and does not necessarily represent the official views of the funding sources.

Results

Both the LG group and the HI group showed significant decreases in the timing of toe-off during the 1-year gait follow-up period. At visit 4, toe-off occurred at about 60% of the gait cycle for both groups. A 2 (group) × 4 (visit) analysis of variance with repeated measures on visit indicated that only visit had a significant effect (F=16.40; df=3,65; P<.001) (Fig. 3A, Tab. 2). Post hoc analyses revealed that the timing of toe-off at visit 3 was significantly earlier than that at visit 1 and that the timing of toe-off at visit 4 was significantly earlier than that at visits 1 and 2 (all P values<.05).

Figure 3.
Figure 3.

Significant results for joint kinematics: (A) timing of toe-off, (B) timing of peak ankle plantar flexion, (C) timing of peak hip flexion, (D) magnitude of peak hip flexion, and (E) timing of peak hip abduction. The LG group received lower-intensity, generalized treadmill training, and the HI group received higher-intensity, individualized treadmill training.

Ankle Plantar Flexion and Dorsiflexion

In both groups, peak ankle plantar flexion occurred at about toe-off at visit 1 and after toe-off at visit 2. At visits 3 and 4, the LG group maintained the timing of peak ankle plantar flexion after toe-off, whereas peak ankle plantar flexion occurred before toe-off in the HI group (Fig. 3B, Tab. 3). On average, peak ankle plantar flexion across all 4 gait visits occurred at 1.6% of the gait cycle (after toe-off) in the LG group and −0.2% (before toe-off) in the HI group. Statistical analysis indicated a significant effect of group (F=4.71; df=1,24; P=.04) and a significant effect of visit (F=5.09; df=3,65; P=.003). Post hoc analyses revealed that the timing of peak ankle plantar flexion was significantly later at visit 2 than at visit 4 for both groups (P<.01). Both groups also showed an increase in the magnitude of peak ankle plantar flexion, from −6 degrees at visit 1 to about −14 degrees at visit 4 (Tab. 3). Statistical analysis revealed a significant effect of visit (F=10.13; df=3,65; P<.001); the magnitudes at visits 1 and 2 were smaller than those at visits 3 and 4 for both groups (all P values<.05).

View this table:
Table 3.

Means and Standard Deviations for Peak Ankle, Hip, and Knee Joint Angles and Statistical Significance

Both groups showed a significant increase in the timing of peak ankle dorsiflexion but maintained the magnitude during the gait follow-up period (Tab. 3). On average, peak ankle dorsiflexion across both groups occurred at 14% of the gait cycle (after toe-off) at visit 1 and 23% (after toe-off) at visit 4. Statistical analysis indicated a significant effect of visit on the timing of peak ankle dorsiflexion (F=19.95; df=3,65; P<.001); the timing at visit 1 was earlier than that at visits 2, 3, and 4 for both groups (all P values<.05).

Hip Extension and Flexion

In both groups, peak hip extension occurred closer to toe-off during the gait follow-up period, from −15% of the gait cycle (before toe-off) at visit 1 to −13% (before toe-off) at visit 4. The effect of visit was significant (F=3.45; df=3,65; P=.02); the timing at visit 1 was significantly different from that at visit 4 for both groups (all P values<.05). In terms of magnitude, both groups showed an increase in peak hip extension, from −1 degree at visit 1 to −6 degrees at visit 4 (Tab. 3). The effect of visit approached statistical significance (F=2.54; df=3,65; P=.06).

Both groups showed steady increases in the duration from toe-off to peak hip flexion during the gait follow-up period (Fig. 3C, Tab. 3). Peak hip flexion occurred later after toe-off in the HI group than in the LG group. On average, peak hip flexion across all 4 gait visits occurred at 18.5% of the gait cycle (after toe-off) in the LG group and 20.9% (after toe-off) in the HI group. Statistical analysis revealed a significant effect of group (F=8.00; df=1,21; P=.01) and a significant effect of visit (F=22.91; df=3,65; P<.001). Specifically, the timing of peak hip flexion was earlier at visit 1 than at visits 2, 3, and 4 for both groups (all P values<.05).

Both groups showed an increase in the magnitude of peak hip flexion during the gait follow-up period (Fig. 3D, Tab. 3). The average magnitudes of peak hip flexion across all 4 gait visits were 35 degrees in the LG group and 32 degrees in the HI group. In particular, the HI group produced a smaller magnitude of peak hip flexion (by ∼4°) than did the LG group at visits 1, 2, and 3. Statistical analysis revealed that the effect of visit was significant (F=3.88; df=3,65; P=.01) and that an effect of group approached statistical significance (F=3.45; df=1,24; P=.08). Specifically, the magnitude of peak hip flexion at visit 1 was smaller than that at visit 4 for both groups (P=.02).

Knee Extension and Flexion

Both groups maintained the timing and magnitude of peak knee extension during the gait follow-up period. Peak knee extension occurred at −23% of the gait cycle (before toe-off), and the magnitude was 17 degrees across the 2 groups over 4 gait visits (Tab. 3). No statistical significance was found for either the timing or the magnitude of peak knee extension. In terms of peak knee flexion, both groups showed increases in timing and magnitude during the gait follow-up period (Tab. 3). When data from the 2 groups were collapsed, peak knee flexion was found to occur at 6% of the gait cycle (after toe-off) at visit 1 and at 10% (after toe-off) at visit 4; the magnitudes were 76 degrees at visit 1 and 88 degrees at visit 4. Statistical analysis revealed a significant effect of visit on the timing of peak knee flexion (F=13.55; df=3,65; P<.001) and a significant effect of visit on the magnitude (F=8.43; df=3,65; P<.001). The timing of peak knee flexion was earlier at visit 1 than at visits 2, 3, and 4, and the magnitudes were smaller at visits 1 and 2 than at visit 4 (all P values<.05).

Hip Adduction and Abduction

In both groups, peak hip adduction was consistently shown to occur at 38% of the gait cycle (after toe-off) during the gait follow-up period (Tab. 3). No statistically significant results were found for the timing of peak hip adduction. In terms of magnitude, both groups showed increases in peak hip adduction, from −4 degrees (ie, abduction) at visit 1 to 5 degrees (ie, adduction) at visit 4. Statistical analysis revealed a significant effect of visit (F=25.03; df=3,65; P<.001); the magnitude of peak hip adduction was smaller at visit 1 than at visits 2, 3, and 4, and the magnitude was smaller at visit 2 than at visit 4 (all P values<.05).

In both groups, the timing of peak hip abduction increased from 8% of the gait cycle (after toe-off) at visit 1 to 13% (after toe-off) at visit 4 (Fig. 3E, Tab. 3). Although the LG group showed continuous increases in the timing of peak hip abduction during the gait follow-up period, the HI group showed decreases in timing at visits 2 and 3 before showing an increase (to 13%) at visit 4. Statistical analysis indicated a significant effect of visit (F=4.61; df=3,65; P=.006) and a marginal group × visit interaction (F=2.59; df=3,65; P=.06). Post hoc analyses revealed that the timing of peak hip abduction was earlier at visits 1 and 2 than at visit 4 for both groups (all Ps<.05). In both groups, the magnitude of peak hip abduction decreased, from about −23 degrees at visit 1 to −14 degrees at visit 4 (Tab. 3). This effect of visit was significant (F=15.48; df=3,65; P<.001); both groups produced a larger magnitude of peak hip abduction at visit 1 than at visits 2, 3, and 4 (all P values<.05).

Discussion

We studied the developmental trajectories of joint kinematic patterns during the first year after walking onset in infants who had DS and who received either an LG treadmill intervention or an HI treadmill intervention. The results indicated that both the LG group and the HI group showed significant decreases in the timing of toe-off, from about 67% of the gait cycle at visit 1 to about 60% at visit 4, during the 1-year gait follow-up period. These data implied that both groups learned to swing their legs forward for a longer duration during walking. Both groups showed significant advances in the timing and magnitude of peak joint angles during the gait follow-up period for most of the variables that we examined. Specifically, in both groups, the timing of peak ankle plantar flexion and hip extension occurred closer to toe-off, and the magnitude of peak ankle plantar flexion increased.

In addition, during the gait follow-up period, both groups learned to increase the duration after toe-off before flexing the hip, knee, and ankle joints and to produce a higher degree of flexion at the hip and knee joints. In addition, in both groups, the timing of peak hip adduction after toe-off increased during the gait follow-up period, and the magnitude of adduction increased while the magnitude of abduction decreased.

All of these developmental trajectories are consistent with those reported in infants with TD.6,8 These data suggested that both the LG and the HI training protocols had positive long-term effects on the development of joint kinematic patterns in infants with DS within 1 year after walking onset.

Consistent with our hypothesis, the HI group showed some aspects of more-advanced joint kinematic patterns than the LG group during the gait follow-up period. The primary group differences were in the timing of peak joint angles and not in their magnitude, in particular, at the ankle and hip joints. For instance, the HI group showed peak ankle plantar flexion at or before toe-off, whereas the LG group consistently showed peak ankle plantar flexion after toe-off. These findings implied that the HI group may have taken advantage of ankle plantar flexion occurring before toe-off to facilitate a mechanical energy transfer from gravitational potential energy to forward kinetic energy.22,23

In contrast, peak ankle plantar flexion occurring after toe-off in the LG group suggested that the LG group may have dragged the foot on the ground at the initial swing phase and made less use of push-off to transfer mechanical energy from the stance phase to the swing phase. In addition, peak ankle plantar flexion occurring before toe-off in the HI group may have facilitated a shift in the location of the center of mass from the ipsilateral leg to the contralateral leg, produced a higher net mechanical output to the swing phase, and yielded an increase in walking speed.23 The timing of peak ankle plantar flexion in the HI group may account, in part, for previous observations of the HI group walking faster than the LG group during the gait follow-up period.17

Besides facilitating mechanical energy transfer, peak ankle plantar flexion occurring before toe-off in the HI group may have facilitated flexion of the hip joint. With a simple bipedal walking model, Kuo24 predicted that increasing ankle push-off is 4 times less energetically costly than using the hip muscles alone. Consistent with this theoretical model, Lewis and Ferris25 showed that increasing ankle push-off can significantly reduce hip flexor forces and peak hip flexion moments during treadmill walking in adults who are healthy. In the present study, peak ankle plantar flexion occurred before toe-off in the HI group but after toe-off in the LG group, although both groups produced similar magnitudes of peak ankle plantar flexion. Toddlers with TD and less than 6 months of walking experience have been shown to produce dominant extending moments at the hip and knee joints and almost no power at the ankle joint.7 We thus suggest that instead of increasing the magnitude of peak ankle plantar flexion, the HI group may have used advanced timing (ie, before toe-off) to reduce the demand on the hip flexor muscles and increase the duration of the forward leg swing before reaching peak hip flexion, as observed in the present study. This timing advantage in the HI group may explain, in part, the observations that the HI group produced less peak hip flexion than the LG group at the first 3 gait visits but produced similar step and stride lengths, as reported elsewhere.17,18 These findings implied that the LG group may have had increased hip muscle forces because of inadequate push-off and may have walked with more of a “marching” pattern by raising the thigh higher during the swing phase at the first 3 gait visits.

Although the HI training protocol was different from the LG training protocol in daily training duration, belt speed, and ankle weight, we believe that the primary difference was in ankle weight.16,19 The data in Table 1 show that the actual daily training duration and belt speed in the HI group were not markedly greater than those in the LG group. The effect of ankle weight has been suggested to explain, to a great extent, the earlier attainment of walking onset, the more mature spatiotemporal parameters during overground walking, and the adoption of adaptive strategies while negotiating an obstacle in the HI group.16–19 The results of the present study indicated that a change of context in a treadmill intervention (ie, adding ankle weight) can facilitate the emergence of coordinated joint kinematic patterns in infants with DS even after the intervention has been terminated. We believe that the inclusion of additional ankle weight in the HI training protocol also would strengthen primary leg muscles, such as the tibialis anterior and gastrocnemius muscles, and that it would elicit the appropriate timing of muscle burst and enhance the alternating burst pattern of the agonist and the antagonist during walking.19 Taken together, all of the results led us to conclude that the HI training paradigm provides a more effective means of advancing the emergence of ankle plantar flexion before toe-off and facilitating hip abduction in the stance phase and hip flexion in the swing phase in infants with DS. This HI training program should be started in the first year of life in infants with DS to provide the greatest benefit to this population.

The significant temporal characteristics (timing) of peak joint angles observed in the HI group demonstrated that an effective physical intervention, such as the HI training protocol, can significantly accelerate the development of joint kinematic patterns in infants with DS, in particular, at the ankle and hip joints. This effect is especially important in the first 6 months or so after walking onset because this time window is markedly associated with rapid gait development in infants with TD1,5,6 and infants with DS.11,17,19 Although the HI training protocol advanced the onset of independent walking to 19.2 months of age in infants with DS, this walking onset was still markedly later than that in infants with TD (ie, ∼12 months of age). It is thus important that after the treadmill intervention was terminated, the HI training continued to accelerate the development of joint kinematic patterns compared with the LG training within 1 year after walking onset. Even though joint kinematic patterns in the LG group approached those in the HI group toward the end of the gait follow-up period, the accelerated development of joint kinematics in the HI group within the first 6 months or so may have facilitated the refinement of walking patterns and the development of other domains, such as cognitive and social domains. Because walking is a fundamental motor skill that allows infants to develop more-advanced gross motor skills and to interact with people and the environment, we believe that the HI training protocol can be an effective intervention for infants with DS.

The raw timing of peak joint angles was not used in the present study; rather, the difference between the raw timing of peak joint angles and the timing of toe-off was calculated. This definition of timing is important when a gait event occurs at about toe-off and the timing of toe-off changes from visit to visit. This definition of timing facilitated the presentation and interpretation of peak ankle plantar flexion and peak hip flexion in the present study. Although we examined only the development of joint kinematic patterns, both kinetic and neuromuscular data, if available, would allow us to further investigate the benefits of treadmill interventions for each aspect of gait development. A recent study14 showed that infants with DS produced an inconsistent muscle activation pattern, longer muscle burst duration, and shorter interburst intervals than did infants with TD within 6 months after walking onset. The inclusion of electromyography equipment would help in the measurement of leg muscle activities, especially at the hip joint, and in the investigation of whether the HI training protocol could have a beneficial effect on the development of neuromuscular coordination in infants with DS.

The Bottom Line

What do we already know about this topic?

A higher-intensity, individualized (HI) treadmill training protocol allows infants with Down syndrome (DS) to walk independently earlier and to be better able to negotiate an obstacle when compared with a lower-intensity, generalized (LG) training protocol. However, it is unknown whether the two protocols lead to the development of different joint kinematic patterns.

What new information does this study offer?

During 1-year gait follow-up, the HI training protocol led to a more accelerated development of joint kinematics and elicited adult-like timing of peak ankle plantar flexion in infants with DS, which helped them to better utilize mechanical energy transfer during walking.

If you're the parent or caregiver of a patient, what might these findings mean for you?

Treadmill intervention, in particular the HI training protocol, is recommended for implementation with infants with DS to advance their walking onset and promote motor development. The intervention should start when infants with DS are about to sit alone and should continue until they achieve independent walking.

Footnotes

  • Dr Wu, Dr Ulrich, and Dr Angulo-Barroso provided concept/idea/research design. Dr Wu and Dr Looper provided writing. All authors provided data collection and data analysis. Dr Wu and Dr Angulo-Barroso provided project management and consultation (including review of manuscript before submission). Dr Ulrich and Dr Angulo-Barroso provided fund procurement. Dr Ulrich provided facilities/equipment. The authors are grateful to all of the participants and their families for their participation in this study, and they thank all of the students and researchers for their contributions to data collection and analysis.

  • This study was approved by the Institutional Review Board at the University of Michigan.

  • This study was supported by a grant from the US Office of Special Education and Rehabilitative Services (H324C010067) and a grant awarded by the March of Dimes Birth Defects Foundation to Dr Ulrich and Dr Angulo-Barroso.

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

  • ↵† Vicon, 5419 McConnell Ave, Los Angeles, CA 90066.

  • ↵‡ The MathWorks Inc, 3 Apple Hill Dr, Natick, MA 01760.

  • ↵§ SAS Institute Inc, 100 SAS Campus Dr, Cary, NC 27513.

  • Received August 27, 2009.
  • Accepted May 4, 2010.
  • © 2010 American Physical Therapy Association

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View Abstract
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Vol 96 Issue 12 Table of Contents
Physical Therapy: 96 (12)

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Effects of Various Treadmill Interventions on the Development of Joint Kinematics in Infants With Down Syndrome
Jianhua Wu, Julia Looper, Dale A. Ulrich, Rosa M. Angulo-Barroso
Physical Therapy Sep 2010, 90 (9) 1265-1276; DOI: 10.2522/ptj.20090281

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Effects of Various Treadmill Interventions on the Development of Joint Kinematics in Infants With Down Syndrome
Jianhua Wu, Julia Looper, Dale A. Ulrich, Rosa M. Angulo-Barroso
Physical Therapy Sep 2010, 90 (9) 1265-1276; DOI: 10.2522/ptj.20090281
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  • Reliability and Validity of Force Platform Measures of Balance Impairment in Individuals With Parkinson Disease
  • Predictors of Reduced Frequency of Physical Activity 3 Months After Injury: Findings From the Prospective Outcomes of Injury Study
  • Effects of Locomotor Exercise Intensity on Gait Performance in Individuals With Incomplete Spinal Cord Injury
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