Abstract
Background The attainment of walking is a focus of physical therapy intervention in children with cerebral palsy (CP) and may affect their independence in mobility and participation in daily activities. However, knowledge of determinants of independent walking to guide physical therapists' decision making is lacking.
Objective The aim of this study was to identify child factors (postural control, reciprocal lower limb movement, functional strength, and motivation) and family factors (family support to child and support to family) that predict independent walking 1 year later in young children with CP at Gross Motor Function Classification System (GMFCS) levels II and III.
Design A secondary data analysis of an observational cohort study was performed.
Methods Participants were 80 children with CP, 2 through 6 years of age. Child factors were measured 1 year prior to the walking outcome. Parent-reported items representing family factors were collected 7 months after study onset. The predictive model was analyzed using backward stepwise logistic regression.
Results A measure of functional strength and dynamic postural control in a sit-to-stand activity was the only significant predictor of taking ≥3 steps independently. The positive likelihood ratio for predicting a “walker” was 3.26, and the negative likelihood ratio was 0.74. The model correctly identified a walker or “nonwalker” 75% of the time.
Limitations Prediction of walking ability was limited by the lack of specificity of child and family characteristics not prospectively selected and measurement of postural control, reciprocal lower limb movement, and functional strength 1 year prior to the walking outcome.
Conclusions The ability to transfer from sitting to standing and from standing to sitting predicted independent walking in young children with CP. Prospective longitudinal studies are recommended to determine indicators of readiness for independent walking.
The attainment of walking is an important goal for families of young children with cerebral palsy (CP) and is a focus of early physical therapy intervention. Cerebral palsy is a chronic disorder of posture and movement.1–3 Early limitations in walking present potential barriers to participation in physical, recreational, and social activities4–7 that may affect development of friendships.8,9 Knowledge of early indicators of future walking ability has particular relevance for children with CP, at Gross Motor Function Classification System (GMFCS) levels II and III, whose trajectory or prognosis for attaining independent walking is more variable in early childhood but who are expected to have limitations in walking outdoors and in the community.1,10 Walking without support, even for short distances, may affect independence in mobility and participation in recreational, leisure, and learning activities.5,11 Palisano and colleagues12 found that children and youth classified at GMFCS levels II and III were 4.6 times more likely to not do any activities with friends or others compared with those who walked without assistance (ie, GMFCS level I).12 Changes in motor abilities occur during a transitional phase of variable movement patterns (ie, a sensitive period), during which intervention might be particularly effective.13,14 Despite advocacy for an early focus on activity through intensive practice to enhance mobility,15,16 knowledge of both child foundational abilities and family support that predict children's ability to take steps independently have not been identified.
Findings from research provide insights on child characteristics associated with the ability to walk without assistance.17–22 Sitting without support18,19 and pulling to stand at age 2 years20 have been associated with future walking. Prospective studies identified reciprocal crawling on hands and knees21 and the number and rate of acquisition of motor milestones22 in the first 30 months as predictive of independent walking. Fedrizzi and colleagues22 found that children with CP who rapidly achieved gross motor skills in the first 2 years (eg, roll from a supine to a prone position and sit without support) walked independently between 3 and 5 years of age. Motor development and percentile curves for children with CP1,23 aid in the prediction of walking; however, variability in motor capability exists within GMFCS levels.23 Identification of determinants of walking is a first step in guiding intervention planning to optimize independent walking.
Our conceptual framework depicts a person-environment model of potential factors associated with taking steps independently. Consistent with the International Classification of Functioning, Disability and Health (ICF),24 this framework illustrates the interaction between child neuromuscular functions and psychosocial aspects within and external to the child. When making clinical decisions regarding when to intensify a focus on independent walking, it is important to consider the dynamic interaction of the child and the daily environment that influences mobility.3,13,25 A minimum child capability on a combination of key neuromuscular functions (postural control, reciprocal lower limb movement, and functional strength) may be an important prerequisite to walking. Child motivation, representing an intrinsic drive to master a challenging skill, has been identified as a determinant of basic motor abilities in children with CP.26,27 Together, child neuromuscular functions and motivation represent “child factors” that may be influential in the development of independent walking. Family support to the child and support to the family (ie, “family factors”) represent the influences of parents and community members who provide an opportunistic environment that may promote independent walking. Determination of child and family environmental factors predicting walking in young children with CP has important implications for an efficient and cost-effective rehabilitation plan.
Postural control, or the ability to maintain balance in antigravity postures, is considered a primary impairment in young children with CP.28,29 Postural control in sitting and standing allows safe performance of everyday tasks and is a prerequisite to independent walking.30 Postural stability in standing has been correlated with an earlier age of independent walking in children with spastic diplegia.31
Reciprocal lower limb movement describes alternating limb movements to advance the body forward through crawling, walking, and running. Reciprocal crawling on hands and knees has been suggested as an important predictor of independent walking in children with CP.18,22,32 Impaired ability to coordinate reciprocal lower limb movement may contribute to a compensatory crawling strategy of simultaneous hip flexion (ie, “bunny-hopping”) that has been associated with the inability to walk independently.18,21
Functional strength describes the coordinated activation of sufficient muscle forces in the lower limbs necessary to move away from the supporting surface to change the position of the body in space (eg, standing from or lowering to a sitting position on a bench). Muscle strength has been associated with attainment of gross motor abilities and shown to indirectly influence functional outcomes in self-care, mobility, and social function in children with CP.32,33 In infants developing typically, the transition to independent walking occurs, in part, through efficient coordination of intersegmental muscle forces and inertia to propel the body forward while upright.34
Motivation in young childhood is a multidimensional construct that includes a child's attempts to master physical skills.35 Children with mastery motivation initiate and adapt motor actions perceived to be challenging, often deriving pleasure from the effort.35 Majnemer and colleagues36 suggested that perseverance and practice to master difficult activities self-promotes learning of novel motor abilities and may be influenced by environmental factors such as child and family support systems.
Family factors include the supports and opportunities provided by the family and others to foster the child's learning of walking during daily activities. Support to the child and support to the family encompass the important role of parents, therapists, teachers, extended family, and community members in providing a stimulating environment for early motor exploration and opportunities for repetition and task-specific practice of emerging child motor abilities. Support to the family empowers parents to coordinate services and orchestrate experiences for their child in the community.37,38
The objective of this study was to identify the child and family factors associated with future ability to take 3 or more steps independently in young children, 2 through 6 years of age, with CP at GMFCS levels II and III. We hypothesized that child factors would have a higher association with independent walking than family factors. More knowledge of determinants of walking may contribute to identification of variables for further study and guide clinical decision making to promote independent walking.
Method
Design and Participants
This cohort study used exploratory associational methods in a secondary data analysis to examine a subsample of 429 young children with CP and their parents who participated in the Move & PLAY (referring to Movement and Participation in Life Activities of Young children) study, a longitudinal study of determinants of motor abilities, self-care, and play in young children with CP. Children were 18 through 60 months of age and were selected from a sample of convenience from 4 regions in the United States and 9 regions in Canada.26,39 Children with a diagnosis of CP or delays in gross motor development and impairments in muscle tone, righting and equilibrium reactions, anticipatory postural movements, and active range of motion during movement were included. Children with other identified diagnoses such as autism or acquired brain injury that may have resulted in developmental issues similar to CP were excluded. The diagnosis of CP was confirmed at the end of the Move & PLAY study for children less than 2 years of age at the beginning of the study.26 Institutional review board approval was obtained, and parents provided informed consent.
Data were analyzed for 80 of 96 children in the Move & PLAY study who were classified at GMFCS levels II and III. The children's distribution of motor involvement included diplegia (n=36 [45%]), quadriplegia (n=23 [28.7%]), hemiplegia and triplegia (n=9 [11.3%] each), and monoplegia (n=3 [3.8%]). Children included in this study were not walking, defined by independent walking less than 3 steps at the beginning of the study. Descriptive characteristics of the participants are presented in Table 1. The children's average age at the beginning of the study was 33.3 months (SD=10.8) and at the end of the study was 45.6 months (SD=10.7). Parents were, on average, 34.2 years of age, and 72% had more than a high school education. Ninety-nine percent of the children received physical therapy during the study year.
Characteristics of Children With Cerebral Palsy and Their Familiesa
Measures
The GMFCS was used to identify children in level II, expected to walk by 4 to 6 years of age without assistive mobility devices (AMDs), or level III, expected to walk by 4 to 6 years of age with AMDs.10 The GMFCS has demonstrated high interrater reliability for children 2 to 12 years of age (kappa=.75) and moderate interrater reliability for children under 2 years of age (kappa=.55).40
Outcome variable: independent walking ability.
The outcome variable, the ability to walk ≥3 steps independently, was measured using item 69 on the Gross Motor Function Measure (GMFM-66).41 The GMFM-66 is an interval-level scale. Items are weighted by difficulty for children with CP and scored on a 4-point ordinal scale (0–3). In the Move & PLAY study, the GMFM-66 was administered with a shortened version, the basal and ceiling approach (GMFM-66 B&C).26 The GMFM-66 B&C tests only items relevant to the child's ability, ordered by level of difficulty, age, and GMFCS level; therefore, as few as 15 items are administered.42 When computing the total score, items below the basal level receive a score of 3, and items above the ceiling level receive a score of 0. The GMFM-66 B&C has demonstrated high concurrent validity with the GMFM-66 (intraclass correlation coefficient [ICC] (2,1)=.987; 95% confidence interval [CI]=.972, .994) and test-retest reliability (ICC [2,1]=.994; 95% CI=.987, .997).42 In our study, a score of 2 (walks forward 3–9 steps) or 3 (walks forward 10 steps) on GMFM item 69 identified a “walker,” and a score of 0 (does not initiate walking forward) or 1 (walks forward <3 steps) on this item identified a “nonwalker”).
Predictor variables: child and family factors.
Six predictor variables were selected based on theory, research, and practice knowledge (eTable). Postural control, defined as the ability to maintain balance in upright antigravity postures, was the sum of scores for postural control in sitting on a bench for 10 seconds with arms and feet free (score of 3 on GMFM item 34) and in standing for 3 seconds with arms free (score of 3 on GMFM item 53). The sum of scores for postural control in sitting and standing was moderately correlated (r=.53) with the measure of children's overall balance used in the Move & PLAY study, the Early Clinical Assessment of Balance (ECAB).43 Reciprocal lower limb movement describes alternating movements between the limbs to advance on hands and knees through crawling reciprocally forward 1.8 m (6 ft) (score of 3 on GMFM item 45).
When item 34 (sitting), 53 (standing), 45 (crawling), or 69 (walks) was not administered, the score was determined based on the psychometric properties of the GMFM-66 B&C version (Tab. 2). A score of 3 was assigned if the item was below the basal level, and the child was administered and received a score of 3 on a related higher item in the same dimension. Similarly, a score of 0 was assigned if the item was above the ceiling level, and the child was administered and received a score of 0 for a related lower item in the same dimension. Three children for item 34, 2 children for item 53, 9 children for item 45, and 25 children for item 69 were not administered a related item to confirm the score of 3 or 0. All children who walked 3 to 10 steps (walkers) physically performed the item.
Gross Motor Function Measure Scoring Using the Basal and Ceiling Approach (GMFM-66 B&C)a
Functional strength, defined as ability to generate and sustain muscle forces to move the body through space in a sit-to-stand task, was measured using 2 items selected from the Pediatric Balance Scale (PBS).44 The PBS item responses are rated on an ordinal scale from 0 (needs assistance to perform) to 4 (able to do task independently). High test-retest reliability (ICC [3,1]=.998) and interrater reliability (ICC [3,1]=.997) have been reported for children aged 5 to 15 years with mild-to-moderate motor impairment.44 The sum of the scores on PBS item 1 (rising to standing from a bench) and PBS item 2 (lowering to sitting on a bench from standing) was used to measure child functional strength. Selected PBS items were chosen to capture the specificity of strength in a closed-chain functional activity utilizing concentric and eccentric muscle force.
Items representing child motivation, family support to child, and support to family were selected by the first author (D.M.B.), with more than 25 years of pediatric clinical experience, to reflect active physical characteristics believed to be important in predicting independent walking. Child motivation describes the internal drive to attempt challenging motor activities and find the effort pleasurable. Child motivation was measured using select items from the Early Coping Inventory (ECI), a 48-item observational tool that measures adaptive behaviors in children aged 4 to 36 months.45 High interrater reliability (r=.80–.94) has been reported for the ECI.46 Selected items describe child adaptability and self-initiated behaviors believed to characterize motivation to learn to walk independently. Scores for parent-rated child behaviors range from 1 (not effective) to 5 (consistently effective) across situations. The sum of scores on 8 ECI items was used to measure child motivation.
Family support to child describes parent expectations and functional adaptations (eg, hand-over-hand assistance to perform a motor activity), which encourages child independence in learning a new skill.47 Family support to child also includes parent-provided activity settings to promote child motor abilities through embedded developmental learning opportunities during daily routines such as negotiating the slide at the playground.48,49
Family support to child was measured with items from 3 measures: Family Expectations of Child Measure (FEC), Family Support to Child Measure (FSC), and a services questionnaire. The FEC and FSC are 5- and 6-item measures, respectively, of parent expectations and support when learning how to play or move around. Developed through a consensus process with parents of young children with CP, these measures have demonstrated content validity and test-retest reliability.26 Two FEC items and 4 FSC items were selected to reflect the parent's willingness to encourage the child to take risks and participate in energetic physical play. Item responses from the 7-point ordinal scale were converted to a 5-point scale to improve interpretation of results. The responses “not at all” and “to a very small extent” and the responses “to a great extent” and “to a very great extent” were collapsed to develop the 5-point scale. The services questionnaire was developed by Move & PLAY investigators to gather information about the focus and processes of therapy interventions.50 Responses ranged from 1 (“not at all”) to 5 (“to a very great extent”). One item was selected to measure the extent parents are able to include therapy recommendations in daily routines. The sum of the scores on selected FEC, FSC, and services questionnaire items was used to measure family support to child.
Support to family describes the extended family and community members often helpful to parents in raising a young child. Support to family was measured using the Family Support Scale (FSS).51 The FSS is an 18-item measure with item responses from 1 (“not at all helpful”) to 5 (“extremely helpful”). The FSS has demonstrated internal consistency (alpha coefficient=.79) and test-retest reliability (r=.91).26 The sum of all FSS items was used to measure support to family.
Procedure
In the Move & PLAY study, 60 physical therapist assessors who did not provide services to the child or family administered child measures. Prior to data collection, assessors participated in a 1-day training workshop and achieved a standard of at least 80% agreement with criterion videotapes for each measure. Seventeen interviewers, including 14 physical therapists, administered parent report measures by telephone interview. Prior to the interviews, they participated in a training teleconference that included perspectives from parent consultants.
The initial test session took place in the family's home or the clinic where the child received services. Assessors classified GMFCS level and administered the GMFM and PBS; children were tested while barefoot. Parents completed the ECI. An average of 7 months (SD=1.9) later, parents completed the FEC, FSC, services questionnaire, and FSS. Interview questions were mailed to parents prior to administration and were completed by 91% of parents through telephone communication. Seven parents (8.8%) completed these measures in paper form returned by mail or at a home or clinic visit. An average of 12.4 months (SD=0.09) after the initial test session, assessors completed the GMFM again.
Data Analysis
Data were analyzed using IBM SPSS version 20.0 (IBM Corp, Armonk, New York). Descriptive statistics for child and family demographics were computed. Mean substitution was used to input a PBS value for one case. Five predictor variables had an approximately normal distribution of scores. The reciprocal lower limb movement variable was dichotomized due to an approximately equal distribution of lowest (0) and highest (3) scores and only 10% of scores of 1 or 2. The dichotomized variable represents “crawlers” (score of 2 or 3) and “noncrawlers” (score of 0 or 1).
Means and standard deviations for continuous variables and frequencies for categorical variables were computed for each group. Differences between walkers and nonwalkers were calculated using independent t tests for continuous variables and chi-square tests for categorical variables. Statistical significance was set at alpha ≤.05 for all analyses. Intercorrelations of predictor variables were examined through Pearson product moment coefficients. Tests for multicollinearity among predictor variables were examined through multiple linear regression analysis.
Logistic regression analysis was used to determine the variables that predicted the ability to walk at least 3 steps independently. All predictor variables were initially entered simultaneously into the model; however, the Hosmer and Lemeshow goodness-of-fit test, (P<.05) indicated the model was not a good fit. To improve model fit, predictor variables were entered using a backward stepwise method. Odds ratios (ORs) and their 95% CI values were calculated for logistic regressions. Sensitivity and specificity of the significant predictor variable were assessed using a receiver operating characteristic (ROC) curve.
Moderate correlations between postural control and other child neuromuscular functions prompted closer examination of this variable through post hoc univariate logistic regression analysis and construction of a ROC curve.
Role of the Funding Source
Grant support for the Move & PLAY study was provided by the Canadian Institutes of Health Research (MOP 81107) and the National Institute on Disability and Rehabilitation Research (H133G060254).
Results
Differences Between Walkers and Nonwalkers
One year after the first assessment, 21 children (26%) were walkers and 59 children (74%) were nonwalkers. Most walkers, 18 of 21 (85.7%), had a score of 3 on GMFM item 69, indicating ability to walk forward 10 steps, and 13 of 21 (62%) also had a score of 3 on GMFM item 70, indicating ability to walk forward 10 steps, turn 180 degrees, and return to start. Most nonwalkers, 54 of 59 (91.5%), had a score of 0 on item 69, either because they could not do the task at all (n=29) or the item was above their ceiling level (n=25). Walkers and nonwalkers did not differ significantly in age or on child and family demographics except for GMFCS classification; 86% of walkers and 25% of nonwalkers were classified at level II. The average age of children classified at level II who were walking (n=18) at the end of the study (X̅=42.2 months, SD=9.5, range=30–58) was only slightly higher than the average age of children classified at level II who were not walking (n=15) (X̅=41 months, SD=9.1, range=31–59) (Tab. 1).
Average scores on predictor variables for the full sample (walkers and nonwalkers) are listed in Table 3. Mean scores for postural control, reciprocal lower limb movement, and functional strength were significantly higher for walkers than for nonwalkers (P<.05). Mean scores for child motivation, family support to child, and support to family did not differ significantly between groups (P>.05) (Tab. 3).
Descriptive Statistics for Hypothesized Predictor Variables
Intercorrelations showed that postural control was moderately related to reciprocal lower limb movement (r=.60, P<.01) and to functional strength (r=.41, P<.01). A low-to-moderate correlation was found between functional strength and reciprocal lower limb movement (r=.32, P<.01). Multicollinearity tests showed no dependency between predictor variables that would bias the regression model.
Factors Associated With Walking
Results of the backward stepwise logistic regression showed that functional strength was the only significant predictor of independent walking (P<.05). The OR for functional strength was 1.45 (95% CI=1.15, 1.83). To determine the odds related to a 3-unit increase in the functional strength score, the regression coefficient, B=.373, is multiplied by 3=1.119 and then raised to that power (e[0.373 × 3]=e1.12=3.06). Thus, the odds of becoming a walker are 3 times greater for a child with a score of 3 than for a child with a score of 0 on this variable.
The logistic regression model accurately classified a walker 33.3% of the time (sensitivity=7/21=.333) and a nonwalker 89.8% of the time (specificity=53/59=0.898) (Tab. 4). The positive likelihood ratio (LR+), an indicator of how many times more likely a positive test will be seen in walkers than in nonwalkers, was 0.333/0.102=3.26. The negative likelihood ratio (LR−), an indicator of how many times more likely a negative test will be seen in walkers than in nonwalkers, was 0.667/0.898=0.74. The overall accuracy of classification was 75% (ie, the model correctly identified a walker or nonwalker 75% of the time).
Classification Table for Observed and Predicted Walking Outcome
The ROC curve for functional strength showed the area under the curve (AUC) to be 0.71 (P<.01; 95% CI=0.57, 0.85), indicating that functional strength discriminated between walkers and nonwalkers significantly better than chance. The coordinates of the ROC curve indicated the optimal level at which to first predict walking corresponds to a cutoff score of 4 (sensitivity=0.524, specificity=0.864) (Fig. 1).
Receiver operating characteristic (ROC) curve for functional strength variable. Coordinates of the optimal level at which to first predict walking: (1 − specificity)=0.14, sensitivity=0.52. Diagonal segments are produced by ties.
Post hoc exploratory analysis showed postural control entered univariately in a logistic regression was a significant predictor of the walking outcome (P<.05). The OR for postural control was 1.63 (95% CI=1.04, 2.56). The ROC curve for postural control showed the AUC to be 0.67 (P<.05; 95% CI=.54, .80) (Fig. 2). The coordinates of the ROC curve showed a sensitivity of 0.762 and a specificity of 0.559 for the highest score of 6.
Receiver operating characteristic (ROC) curve for postural control variable. Coordinates at which to optimally predict walking: (1 − specificity)=0.44, sensitivity=0.76. Diagonal segments are produced by ties.
Discussion
This study examined a person-environment model of child and family factors that predict taking independent steps in young children with CP, ages 18 to 57 months, classified at GMFCS levels II and III. The results indicated that functional strength measured in a closed-chain sit-to-stand task was the only predictor of ability to take 3 or more steps independently after 1 year. Previous studies demonstrated significant improvements in muscle strength using multijoint exercises similar to everyday activities, including squat-to-stand and sit-to-stand.52–54 The results of this study support measurement of sitting to standing and standing to sitting, a dynamic functional strength activity, to indicate when a child may be ready to learn a new mobility method of taking steps without support of a person or AMD.
The ROC curve for functional strength indicates a higher probability of walking in children who need minimal aid to stand from a bench or to stabilize, reflecting ability to generate and sustain muscle forces to move the body through space. Strengthening programs for children with CP emphasizing closed-chain exercises mimicking everyday activities have been shown to increase strength and functional ability.55 Some studies showed improvements in lower limb muscle strength, sit-to-stand and squat-to-stand activities, and motor abilities in standing and walking through targeted strengthening.52,54,56–58 Studies examining treadmill training support functional strengthening in a closed-chain activity that is specific to the task of walking.59–61 To prepare for walking, our study supports training of muscle strength in closed-chain functional activities.
The model improved the probability of predicting walking. However, the low sensitivity of the functional strength variable suggests its limitations as a sole predictor of independent walking. Exploration of cases that did not follow the predictive criterion (ie, walkers scoring 0 [low] [n=5] and nonwalkers scoring ≥5 [high] [n=6] on the functional strength variable) were examined descriptively. Among children with low functional strength, all walkers (5/5) and 53% (16/30) of nonwalkers were under 3 years of age at the beginning of the study. Also among children with low functional strength, 60% (3/5) of walkers and 30% (9/30) of nonwalkers had procedures for spasticity management during the year. Among children with high functional strength, only 14% (1/7) of walkers but 50% (3/6) of nonwalkers were hospitalized for medical reasons such as seizures. These cases illustrate that factors such as age, medical management, and other health conditions potentially moderate when a young child with CP is on the verge of taking independent steps.
Different from previous studies identifying an association between early motor milestones and future walking,20–22 this study sought to identify factors predicting walking within a specified time frame. The 1-year interval between measurement of neuromuscular functions and ability to take steps independently may be too long to capture dynamic changes in the child interacting with the daily environment.62 Some walkers who did not perform the sit-to-stand task might have improved functional strength following the initial test session, which could have been determined had the predictors been measured at repeated intervals. As proposed by Thelen and Ulrich,13 developmental subsystems progressing at their own rate converge at a critical time to contribute to independent walking. These results provide preliminary data for prospective studies using frequent measurement of strength in a dynamic functional activity to temporally link neuromuscular functions to independent walking. A framework to guide therapists in determining when a child has the foundational abilities indicating he or she is at or near the point of taking steps independently (ie, “ready” to walk) has relevance for intervention planning to practice walking with less assistance during daily activities. Knowledge of walking predictors will be useful in determining readiness for independent walking.
The results of the logistic regression suggest that static measures of postural control in sitting and supported standing and reciprocity moving on hands and knees are not good predictors of independent walking. The correlation among our indicators of functional strength (bench sit-to-stand), postural control (bench sitting and standing without support), and reciprocal lower limb movement indicates the activities are not independent of each other. When examined separately, postural control was significantly associated with the walking outcome. However, more than half of the children who were able to sit on a bench for 10 seconds and stand for 3 seconds did not achieve the walking outcome. Our findings suggest that a measure of strength during movement in a closed-chain functional activity that includes a component of dynamic postural control was the best predictor of independent walking.
Based on our findings, we recommend examining whether ability to walk with one-hand support for balance predicts readiness to take steps independently. Walking with less hand support more closely demonstrates the task specificity of learning to walk independently. Children with CP exhibit immature balance reactions and walking patterns similar to infants with typical development who walk with support.63–65 Postural control with hands free of support during the stance phase of walking is a prerequisite of independent walking.66 Early opportunities to practice postural control while walking with less hand support might initiate a phase shift toward development of mature balance reactions and learning of independent walking through repetitive everyday walking experience.13,34 Reduced hand support during walking, therefore, is a potential indicator of readiness to take steps independently.
The finding that the child's motivation, family support to the child, and support from others were not predictors of the child's ability to take steps independently should be cautiously interpreted. These are general measures of these constructs and were not contextualized to walking. In keeping with the conceptual framework of the ICF, further research is recommended to examine personal factors (eg, child motivation to walk) and environmental factors (eg, family readiness to provide opportunities for practice of walking with less assistance at home and in the community). At present, measures have not been validated specific to the context of walking.
A small sample and secondary data analysis were limitations of this study. Prospective studies are needed to select predictive measures that are task-specific to walking independently. In addition to the recommendations above, a measure of functional strength and dynamic postural control while swinging the lower limb forward to initiate a step may increase the sensitivity of predicting readiness for walking. Similarly, reciprocal stepping on a treadmill, a task-specific walking activity, may be an indicator of readiness to take steps independently.59,61 Further research is recommended to determine neuromuscular functions (eg, functional strength, postural control, reciprocal lower limb movement) that predict independent walking and to contribute to understanding readiness for walking during sensitive periods.
Implications for Practice
Clinical decision making about physical therapy interventions to promote readiness for change in walking ability may require ongoing assessment. Motor development is nonlinear, progressing with age and experience.13,25 Our results indicate that among young children with CP, a child who is able to independently transition from a sitting to a standing position and back may be ready for a more intense focus on learning independent walking; however, a child who is unable to perform this task is not likely ready for walking. Sitting and standing from a chair, an important daily activity at preschool, is an integrated way of repeatedly assessing and practicing muscle strength in a single dynamic functional activity.
This observational study did not address the potential to improve walking with practice in young children with CP classified at GMFCS levels II and III. In a seminal study, Adolph and colleagues34 found that, in addition to strength and balance, experience is an important factor in the development of independent walking in infants developing typically. However, evidence of the amount of practice needed to attain independent walking in children with CP is lacking. Effective collaboration with parents and community partners may increase the amount of task-specific practice of functional strength and walking in activities that are challenging and fun.50 For instance, climbing on playground equipment, walking on ramps or stairs, and pedaling tricycles afford opportunities for functional strengthening in closed-chain activities. Walking practice with less assistance can be incorporated into daily routines and recreational programs.
The aim of this study was to test a model of predictors of walking in young children with CP at GMFCS levels II and III. A sit-to-stand task, operationally defined as an indicator of functional strength, was predictive of taking 3 or more steps independently. Static postural control, reciprocal lower limb movement during crawling, child motivation, family support to child, and support to family did not predict independent walking. Prospective longitudinal studies using a time-series design are needed to examine functional strength and task-specific walking with less assistance as potential indicators of readiness for independent walking. This work ultimately could contribute to development of a clinical prediction rule for independent walking in young children with CP.
Footnotes
Dr Begnoche, Dr Chiarello, and Dr Palisano provided concept/idea/research design. All authors provided writing. Dr Begnoche, Dr Chiarello, and Dr Gracely provided data analysis. Dr Chiarello provided project management and fund procurement. Dr Chiarello, Dr Palisano, Dr Gracely, Dr McCoy, and Dr Orlin provided consultation (including review of manuscript before submission).
This research was completed in partial fulfillment of Dr Begnoche's PhD degree in rehabilitation sciences.
The authors acknowledge the following Move & PLAY study coinvestigators: Doreen J. Bartlett, PhD, Lynn Jeffries, PhD, and Alyssa LaForme Fiss, PhD. Grant support for the Move & PLAY study was provided by the Canadian Institutes of Health Research (MOP 81107) and the National Institute on Disability and Rehabilitation Research (H133G060254).
Ethics approval for the Move & PLAY study was provided by 13 institutional review boards in the United States and 8 ethics committees in Canada.
- Received July 29, 2014.
- Accepted June 8, 2015.
- © 2016 American Physical Therapy Association
References
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