WHAT THIS EVIDENCE ADDS

Current evidence: Evidence suggests that independent mobility is an important facilitator of development across multiple domains.1,2,13–21 However, evidence is less clear regarding benefits of the specific skill of crawling on hands and knees.22

Gap in the evidence: Pediatric physical therapists' (PTs') beliefs and clinical approaches regarding crawling have not been quantified.

How does this study fill this evidence gap? This study reports the results from a national survey of pediatric PTs. Therapists were asked to report their beliefs about crawling, preferred approaches for managing crawling in clinical practice, and their opinions on the 2022 update that eliminated crawling from the Centers for Disease Control and Prevention (CDC) developmental milestone checklists. Most pediatric PTs strongly value crawling and believe that crawling is important for a variety of developmental outcomes. These beliefs are linked with clinical approaches that include training crawling and discouraging other forms of locomotion, and with disagreement with the CDC update.

Implication of all the evidence: Our results suggest that perspectives of pediatric therapists may be at odds with the currently limited research evidence regarding the benefits of crawling. Additional research is needed to investigate hypotheses generated by the clinical community. Examining the role of crawling and other forms of locomotion in the development of motor, sensory, and cognitive skills, and the effects of intervention strategies focused on crawling, may be priorities for future research.

INTRODUCTION

Motor milestones are a salient marker of infant development. Parents excitedly share videos of their children's first steps and worry when their infant cannot roll over at the same age as their peers. Pediatric physical therapists (PTs) and other early intervention providers measure motor skills using standardized assessments to quantify developmental delay, justify therapy services, and set treatment goals. The emergence of motor skills draws attention for multiple reasons. First, attaining motor skills on a normative timeline provides an indication that development is proceeding typically; failure to perform particular skills at particular ages can be an early indicator of neurodevelopmental disability. Second, early motor skills contribute to exploration, learning, and participation and therefore promote global development.1,2

A primary goal of pediatric physical therapy intervention is to promote early motor skills. But which skills should be prioritized? These decisions are, to some extent, arbitrary, influenced by the whims and biases of the early pioneers of motor development research3,4 and the developers of standardized assessments5,6 who selected some skills at the expense of others.7 Given this inherent arbitrariness, a reasonable approach is to focus on skills that are most important for participation and development.

One skill that clearly meets this standard is independent mobility. The ability to locomote, whether accomplished by ambulation or power mobility, contributes to daily functioning, independence, and participation in children with disabilities.8–12 In typical infant development, evidence suggests that self-propelled locomotion, especially walking, enriches everyday interactions with the physical and social environment13–18 and has cascading effects on perceptual, cognitive, social, and communicative development.1,2,19–21 Clinical decisions to promote independent mobility, and walking when appropriate, are thus supported by current developmental and rehabilitation science.

What about the iconic early locomotor skill of crawling on hands and knees (referred to on some standardized assessments as “creeping”)? Contrary to conventional wisdom, there is little evidence for specific effects of crawling experience on developmental outcomes.22 In addition, considerable variability in the timing and form of prewalking mobility23,24 and well-known cross-cultural differences7,25,26 suggest that the prototypical hands-and-knees crawl is not a universal or essential developmental milestone. The omission of crawling from the most recent version of the Centers for Disease Control and Prevention (CDC)'s “Learn the Signs. Act Early” developmental milestone checklists has been debated among pediatric PTs in the United States,22 leading to increased discussion of the role of crawling in development and the implications for pediatric PT practice.

Beliefs about skills such as crawling may impact how pediatric PTs evaluate and treat young children with motor impairments. Therefore, the aims of this study were to characterize beliefs and clinical approaches of pediatric PTs in the United States and to examine relations between beliefs and clinical approaches. Specifically, we asked: What are PTs' beliefs about the role of crawling and independent mobility in infant development, and what sources inform these beliefs? How do PTs manage crawling and early mobility in clinical practice? To what extent do PTs agree or disagree with the removal of crawling from the CDC milestone lists? And are clinical approaches and opinions on the CDC update associated with beliefs about crawling? Finally, we examined the effect of pediatric PT experience to determine whether beliefs and clinical approaches differed between more and less experienced therapists.

METHODS Participants

Participants were recruited through social media and national/state email listservs between October 2022 and February 2023. Individuals were eligible to participate if they were PTs working in pediatrics in the United States. Eligibility was confirmed via screening questions at the start of the questionnaire. The study was approved by the Institutional Review Board at the University of Southern California.

Procedure

The questionnaire was administered online via a secure REDCap database. Following the screening questions, participants provided demographic information, including their location, practice settings, education, and years of pediatric experience. Participants were then presented with a series of statements about crawling and early mobility and asked to rate their agreement with each statement on a 5-point Likert scale ranging from strongly agree to strongly disagree. Four statements assessed participants' overall beliefs about crawling and early mobility, 16 assessed beliefs about specific effects of crawling, 3 assessed clinical approaches surrounding crawling and early mobility, and 1 assessed agreement with the removal of crawling from the CDC milestone checklists. Three additional miscellaneous statements were included in the survey but are not reported here due to space limitations. Participants were also asked to select the sources of information that informed their opinions about crawling. For each source selected, participants were asked to optionally provide more detail; for example, those who selected “basic science principles” were asked “Please describe basic science principles informing your opinion.” Finally, participants were asked a set of open-ended questions that are not analyzed here. The full text of all survey questions is available in Supplemental Digital Content 1, available at: https://links.lww.com/PPT/A495.

Data Analysis

Data from Likert items and multiple-choice items are presented descriptively as proportion of responses. Likert outcomes were considered ordinal data. As associations between ordinal items cannot be assumed to be linear, Spearman's correlations were used to examine relations between items within categories (ie, intercorrelations between beliefs about crawling and intercorrelations between clinical approaches). Spearman's correlations were also used to assess associations between beliefs and clinical approaches, and associations between beliefs and CDC opinions. Correlation coefficients and P values were calculated using the rstatix package in R (cor_mat/cor_pmat functions).

Ordinal logistic regression was used to examine 2 other sets of predictors of beliefs and clinical approaches. Ordinal logistic regression is an extension of binary logistic regression that models effects of predictor variables on shifts between levels of an ordinal outcome measure. Model coefficients represent the log odds of moving to a higher level on the ordinal outcome for each unit increase in the predictor (slopes) and the log odds of responding at each level or lower compared with the next level or higher (intercepts). The first set of models investigated the effect of experience on item responses; they were fit for 3 belief items, 3 clinical approach items, and the CDC item, with years of pediatric PT experience as a continuous predictor. The second set of models investigated the effect of information sources on beliefs; they were fit for the 3 belief items and included 4 information sources as binary predictors. Models were fit using the ordinal package in R (clm function). For all models, we report coefficient estimates and standard errors for the slopes (primary effects of experience and information sources); coefficient estimates and standard errors for the intercepts (representing transitions between adjacent pairs of Likert response levels) are provided in Supplemental Digital Content 2, available at: https://links.lww.com/PPT/A496. The alpha value is 0.05 for all analyses.

Qualitative responses were not formally analyzed in the current article. Summaries and selected quotations from the questions regarding information sources are included to add context to the quantitative results.

RESULTS Sample Demographics

A total of 507 individuals responded to the survey. We excluded 84 unfinished responses and 3 responses from physical therapy assistants for a final sample of 420 participants.

The 331 participants (78.8% of the sample) who reported their location came from 40 US states and the District of Columbia; the greatest number of participants were from: California (17.2%), Nebraska (10.0%), Texas (6.7%), Florida (5.1%), Illinois (4.8%), and Washington (4.8%). Participants' pediatric PT experience ranged from 0 (first year of practice) to 50 years (M = 16.18, median = 13). The most commonly reported (non–mutually exclusive) practice settings were outpatient (57.4%), early intervention (35.0%), and school (23.3%). Most participants (69.5%) had completed a doctoral degree (65.7% DPT/3.8% PhD).

Beliefs About Mobility and Crawling

Figure 1a illustrates responses for the 4 items focused on beliefs about independent mobility and crawling. Nearly all participants (99.1%) agreed or strongly agreed with the statement “Independent mobility is important for development.” Participants were only slightly less likely (91.9%) to agree or strongly agree with the statement “Crawling on hands and knees is important for development”; only 2.6% disagreed or strongly disagreed with this statement. Responses were more evenly distributed (44.1% agree or strongly agree, 32.1% disagree or strongly disagree) for the item “Crawling on hands and knees is a necessary precursor to walking.” And a majority (62.3%) agreed or strongly agreed with the statement “If a child skips crawling, or crawls in a manner different from hands and knees crawling, this has lasting effects on their development.” The 3 crawling beliefs items were moderately and significantly intercorrelated (Table 1, pink cells); the independent mobility belief item was not significantly correlated with any other items.

Fig. 1.:

Distribution of responses to items about (a) overall beliefs about crawling and independent mobility, (b) clinical approaches surrounding crawling and early mobility, and (c) removal of crawling from the CDC developmental surveillance checklists. Text is identical to the questionnaire items as presented to participants. CDC indicates Centers for Disease Control and Prevention.

TABLE 1 - Spearman's Correlation Coefficients for Beliefs and Clinical Approaches B1
Independent mobility is important B2
Crawling is important B3
Crawling is a necessary precursor B4
Not crawling has lasting effects C1
Discourage alternate forms of floor mobility C2
Train crawling for child with alternate form of floor mobility C3
Train crawling for walker who skipped crawling B1
Independent mobility is important 1.00 B2
Crawling is important 0.13 1.00 B3
Crawling is a necessary precursor 0.03 0.57a 1.00 B4
Not crawling has lasting effects 0.05 0.58a 0.58a 1.00 C1
Discourage alternate forms of floor mobility 0.03 0.50a 0.49a 0.49a 1.00 C2
Train crawling for child with alternate form of floor mobility 0.09 0.54a 0.47a 0.54a 0.52a 1.00 C3
Train crawling for walker who skipped crawling –0.02 0.45a 0.40a 0.50a 0.34a 0.56a 1.00 aPFigure 1 for exact text of questionnaire items.

To visualize the relations between pediatric PT experience and item responses, Figure 2 depicts participants' pediatric PT experience grouped by response to each item. Of the 3 beliefs about crawling, 1 was significantly associated with years of pediatric PT experience (Table 2, Model 1, rows 1-3 and Figure 2, top row): Participants with more experience were less likely to agree that skipping crawling has lasting effects on development. This effect was small, with an odds ratio (OR) very close to 1 (1.02; each additional year of experience is associated with a 2% increase in the odds of moving to a less agreeable response).

Fig. 2.: Years of experience in pediatric PT, grouped by response to each item. Center lines depict medians. Hinges (outer bounds of the boxes) depict the 25th and 75th percentiles. Whiskers depict the range of values within 1.5 times the interquartile range from the hinges. Dots depict outlier points beyond 1.5 times the interquartile range from the hinges. Asterisks indicate responses that were significantly associated with years of pediatric PT experience. Plot titles are abbreviated; see Figure 1 for exact text of questionnaire items. CDC indicates Centers for Disease Control and Prevention; PT, physical therapist. TABLE 2 - Ordinal Logistic Regression Model Results Model 1: Experience Model 2: Information Sources Years of Experience Basic Science Principles Research Expert Opinion Clinical Experience B SE B SE B SE B SE B SE B2 0.012 0.008 –0.958a 0.234 0.358 0.207 –0.044 0.206 –0.333 0.318 B3 0.013 0.007 –0.755a 0.214 0.060 0.337 –0.136 0.177 –0.323 0.279 B4 0.019b 0.008 –0.869a 0.219 0.423c 0.182 –0.212 0.181 –0.398 0.280 C1 0.016c 0.007 C2 0.021b 0.008 C3 0.021b 0.007 CDC –0.017c 0.007

Abbreviations: B, coefficient estimates (on logit scale); CDC, Centers for Disease Control and Prevention; SE, standard error of the estimate.

aPFigure 1 for text of questionnaire items.

bP < .01.

cP < .05.

Sources of Beliefs. Participants' opinions about crawling were mostly informed by clinical experience (88.8%), basic science principles (76.4%), expert opinion (51.0%), and peer-reviewed research (46.7%); few participants were informed by Web sites or public media (11.9%).

The responses to open-ended questions provide additional insight into the use of these information sources. For example, in response to the prompt to “describe basic science principles informing your opinion,” participants mostly discussed strengthening of specific muscle groups, benefits of weight-bearing for bone development and proprioceptive input, and the use of reciprocal movement to provide input to both hemispheres of the brain and promote bilateral coordination.

Notably, when probed to “describe clinical experiences that informed your opinion,” participants provided diverging accounts. For example, to support the importance of crawling, 1 therapist wrote, “I have noticed a trend that my children that skipped crawling tend to have a weaker core, weaker upper extremities, sometimes weaker [lower extremities], decreased bilateral coordination and frequently may have asymmetrical or atypical gross motor skills.” Others wrote about effects farther afield, for example, “The school age students that I work with who skipped crawling typically struggle ... with coordination, speech, and academics, especially reading.” Conversely, a therapist who was unconvinced of crawling's importance wrote, “I have seen children who have used alternative methods such as scooting, side crawling or power mobility and have developed higher level motor and cognitive skills without ever having properly crawled on hands and knees.” Another wrote, “I have worked with many children that haven't crawled and have ... no/minimal difficulties with strength/bilateral coordination. I also know several children that ... bottom scooted, and met all other gross motor milestones appropriately and went on to be high school athletes.”

Beliefs about crawling were not significantly associated with whether those beliefs were informed by clinical experience or by expert opinion (Table 2, Model 2, rows 1-3). Those whose beliefs were and were not informed by clinical experience reported similar beliefs about crawling, as did those whose beliefs were and were not informed by expert opinion. However, participants whose beliefs were informed by basic science principles were more likely to agree that crawling is important for development (OR = 0.38), that crawling is a necessary precursor to walking (OR = 0.42), and that skipping crawling has lasting effects on development (OR = 0.47). Conversely, those whose beliefs were informed by peer-reviewed research were less likely to agree that skipping crawling has lasting effects on development (OR = 1.53).

Specific Effects.Figure 3 illustrates participants' beliefs about specific effects of crawling experience. Contributions of crawling for all 8 specific effects were agreed or strongly agreed with by a majority of participants (ranging from 98.8% for upper extremity and shoulder girdle strength to 71.1% for cognitive skills). Necessity of crawling for 3 specific effects; upper extremity and shoulder girdle strength, bilateral coordination, and trunk strength, were also agreed or strongly agreed with by a majority of participants (64.9%, 58.8%, and 57.3%, respectively).

Fig. 3.:

Distribution of responses to items about specific effects of crawling. Text is identical to the questionnaire items as presented to participants.

Clinical Approaches

Figure 1b illustrates responses for the 3 items focused on participants' clinical approaches related to crawling and mobility. When working with a child who uses a method of floor mobility other than hands and knees crawling, 82.3% report that they would try to train hands and knees crawling, and 50.5% report that they would discourage the alternative method. These responses were moderately and significantly correlated (Table 1, blue cells). When working with a child who is walking but skipped crawling, 38.4% report that they would try to train hands and knees crawling. Responses to this item were moderately and significantly correlated with responses about training crawling for a child with an alternative form of floor mobility and weakly but significantly correlated with responses about discouraging an alternative form of floor mobility.

The green cells in Table 1 list correlations between beliefs and clinical approaches. The independent mobility belief was not correlated with clinical approaches, but all 3 beliefs about crawling were moderately and significantly correlated with all 3 clinical approaches. Participants who more strongly endorsed beliefs about the importance of crawling, the status of crawling as a necessary precursor, and the existence of lasting effects due to skipping crawling, were more likely to train crawling and discourage alternative mobility methods in their patients/clients.

Clinical approaches were significantly associated with years of pediatric PT experience (Table 2, Model 1, rows 4-6 and Figure 2, middle row). Participants with more experience were less likely to discourage alternative forms of floor mobility and train crawling. These effects were small (all ORs = 1.02).

Centers for Disease Control and Prevention Update

Figure 1c illustrates opinions about the removal of crawling from the CDC milestone checklists. A majority of participants (78.6%) disagree or strongly disagree with the change. Beliefs about crawling were strongly correlated with opinions about the removal of crawling from the following checklists: −0.67 for importance, −0.60 for necessary precursor, and −0.64 for lasting effects (P values <.001).

Opinions about removal of crawling from the checklists were significantly associated with years of pediatric PT experience (Table 2, Model 1, row 7 and Figure 2, bottom row). Participants with more experience were more likely to agree with the removal of crawling. This effect was small (OR = 0.98).

DISCUSSION

This study characterized pediatric PTs' beliefs and practices regarding early mobility and crawling. Results indicate that most American pediatric PTs strongly value crawling on hands and knees and believe this milestone is important for a variety of developmental outcomes. These beliefs are linked with clinical approaches that include training crawling and discouraging other forms of locomotion.

The belief that independent mobility is important for development, nearly universally endorsed by pediatric PTs in this study, aligns with evidence demonstrating effects of independent locomotion on perceptual, cognitive, and social outcomes.19,20 Strikingly, Nearly as many PTs believed that hands-and-knees crawling specifically is important for development, and a smaller majority believed that failure to crawl has lasting developmental effects, as these beliefs rest on uncertain empirical evidence.22 Outcomes believed to be influenced by crawling were wide-ranging. Effects on gross motor outcomes (upper extremity/trunk strength and bilateral coordination) were the most endorsed, but effects on sensory, neurologic, fine motor, and cognitive outcomes were also endorsed by many participants; 33% to 48% of participants reported that crawling experience is necessary for the development of these outcomes.

Why are beliefs about the importance of crawling so pervasive? Beliefs may be partially influenced by misinterpretation of existing research. For many infants, crawling onset is also the onset of independent mobility; therefore, in most studies, the independent variable of crawling status is confounded with general mobility status.19,20 Readers might interpret findings from such studies as evidence of the benefits of crawling when independent mobility may be the key ingredient. Interestingly, several studies show similar outcomes when precrawling infants gain locomotor experience using a baby walker or powered mobility device,20,27,28 and many show benefits of walking over crawling.13,15,17,18 In addition, our findings suggest that this evidence is not well known by pediatric PTs. Of 420 participants, 196 stated that their opinions were informed by peer-reviewed research; however, only 8 elected to provide citations. Participants who reported that their opinions were informed by research were less likely to agree that skipping crawling has lasting effects on development, indicating that greater exposure to research may influence therapists' views on this topic.

In the absence of empirical evidence, clinicians rely on logic derived from basic science principles. Indeed, basic science principles, drawn from biomechanics, anatomy, and neuroscience, informed beliefs about crawling for 76% of pediatric PTs, and the use of basic science principles predicted greater agreement about the importance of crawling, status of crawling as a necessary precursor, and long-term effects of skipping crawling.

Clinical experience was the most frequently reported informational source, both for those who believed that crawling was important and those who did not. But the 2 groups reported contrasting clinical experiences, with some reporting observations of noncrawlers experiencing a range of difficulties later in development and some reporting the opposite. What accounts for this contrast? One interpretation is that different experiences lead to different beliefs. An alternative explanation is that therapists interpret their clinical experiences through their own belief systems, a phenomenon known as confirmation bias.29 The strong influence of cognitive biases in interpretation of anecdotal clinical data supports the necessity of rigorous research to answer empirical questions.

Our findings also provide insights into what pediatric PTs do in their typical clinical practice. We presented participants with 2 clinical situations: a child who used an alternative method of floor mobility (eg, bottom scooting), and a child who was already walking but skipped crawling. Not surprisingly, most respondents said they would train the first child to crawl; more surprisingly, almost 40% reported that they would “go back” and train crawling for the second child. Perhaps most surprisingly, half of participants stated they would discourage the first child from using their alternative method of mobility. In other words, they would eliminate a child's ability to be independently mobile if the method of mobility was not hands-and-knees crawling. This approach is contraindicated by current evidence on the importance of early mobility.19,20 These clinical approaches were associated with stronger beliefs about the importance of crawling, indicating that therapists' beliefs influence their clinical decision-making.

Given the strong opinions about crawling reported by our study sample, the substantial disagreement with the decision to remove crawling from the CDC's “Learn the Signs. Act Early” developmental milestone checklists was not surprising. A therapist who believes that skipping crawling has lasting effects on development would want children who do not crawl to be flagged for assessment and intervention. As we have discussed elsewhere,22 the exclusion of crawling, a highly variable milestone with limited normative data, was consistent with the CDC's goals to simplify materials for use by families and to ensure that the materials are evidence-based. Ongoing research will be important to assess the effect of these revisions on referrals for comprehensive developmental assessments and early intervention services.

Over the last decades, theoretical perspectives taught in physical therapy textbooks and graduate programs have shifted from neuromaturational, reflex-hierarchical models that emphasized a strict series of milestones driven by brain development to dynamic systems, perception-action, and other approaches that emphasize flexible solutions to varying physical and task constraints.30 We therefore expected that more recently educated therapists would be less likely to endorse the necessity of crawling. Our analysis of the effects of pediatric PT experience suggests that this was not the case; if anything, newer therapists are more enthusiastic about crawling and clinically more likely to focus on crawling at the expense of other forms of mobility. This suggests that the historical shifts in theoretical perspectives are not influencing beliefs and practices regarding crawling. (Note that the continuing influence of neuromaturational theory is also seen in the 71% of participants who believe that crawling contributes to, and the 45% who believe that crawling is necessary for, integration of reflexes.)

We have described pediatric PTs' beliefs and practices as occasionally at odds with current research. However, we note that the literature on infant crawling is scarce and often unsatisfying. Crawling status is difficult to manipulate. As therapists are aware, turning noncrawlers into crawlers is challenging, and turning crawlers into noncrawlers cannot be accomplished by ethical means. Therefore, existing evidence linking crawling experience to developmental outcomes is correlational, not causal. Clinical research must include perspectives from stakeholders, including clinicians, and should consider hypotheses generated by practicing therapists. Our results suggest that examining the role of crawling and other forms of locomotion in the development of upper extremity and trunk strength, coordination, fine motor skills, and sensory, perceptual, and cognitive systems, as well as the effects of intervention strategies focused on crawling, may be priorities for future research.

LIMITATIONS

The results of this study may be affected by selection bias, as pediatric PTs with stronger opinions about crawling may have been more likely to participate. In addition, although the language of the survey items was vetted by the authorship team (all pediatric PTs), items were not externally validated or formally evaluated regarding potential for bias. Finally, our conclusions are limited to the population of PTs practicing in the United States. In future work, it would be interesting to compare beliefs and practices between different countries where PT training and prevailing theoretical approaches may differ. It may also be revealing to compare across different clinical professions; for example, occupational therapists and pediatricians may have different beliefs about crawling.

CONCLUSIONS

Our study revealed that pediatric PTs in the United States believe, based primarily on their clinical experience, basic science principles, expert opinion, and research, that both independent mobility in general and hands-and-knees crawling specifically are important for infant development. These beliefs affect their clinical approaches when working with children who do not demonstrate this form of locomotion, and their opinions about the inclusion of crawling on developmental surveillance milestone checklists. Educational efforts about the “Learn the Signs. Act Early” program and the current state of the evidence surrounding crawling/early mobility, as well as additional research, may be warranted to move the field toward an evidence-based consensus.

ACKNOWLEDGMENTS

The research team received funding from NICHD R01 HD101900. Dr Kretch was supported by NICHD K12 HD055929. The use of REDCap at the University of Southern California was supported by NCATS UL1TR001855 and UL1TR000130.

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