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EPIDEMIOLOGY

Movement Skills and Physical Activity in Obese Children

Randomized Controlled Trial

CLIFF, DYLAN P.1; OKELY, ANTHONY D.1; MORGAN, PHILIP J.2; STEELE, JULIE R.3; JONES, RACHEL A.1; COLYVAS, KIM4; BAUR, LOUISE A.5

Author Information
Medicine & Science in Sports & Exercise: January 2011 - Volume 43 - Issue 1 - p 90-100
doi: 10.1249/MSS.0b013e3181e741e8
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Abstract

Worldwide increases in prevalence (35), particularly in industrialized countries, have caused obesity to become an international public health issue for children and youth (19,39). The need for appropriate treatment interventions for child and adolescent obesity is apparent, although the evidence base is limited by underpowered studies with methodological weaknesses and minimal long-term follow-up (24).

Efforts to treat pediatric obesity would benefit from a better understanding of effective strategies to elicit change in obesity-influencing behaviors such as physical activity and sedentary behaviors (24). A recent systematic review examining the impact of child and adolescent obesity treatment programs on physical activity concluded that the evidence base was limited in both quantity and quality (3). Only two of the 20 studies included in the review assessed physical activity using accelerometry (15,37), and one of those studies was a pilot randomized controlled trial (RCT) that had limited power (15). None of the reviewed studies evaluated a program uniquely designed to address overweight children's movement skill proficiency (21) and perceptions of competence in the physical activity domain (10). Studies testing innovative, theoretically driven treatment approaches that use robust methodologies and have adequate follow-up are required to better understand generalizable approaches for promoting physical activity participation and for reducing sedentary behaviors among overweight youth.

To address these evidence gaps, the current study examined the impact of a competence motivation theory (38) framed physical activity intervention targeting movement skill development. The intervention comprised face-to-face group sessions, a developmentally appropriate home-based physical activity program, and a short behavior-change program with parents. This study reports the program's efficacy, alone and when combined with a parent-centered dietary modification program, for promoting movement skill proficiency, perceived athletic competence, and physical activity and for reducing screen behaviors in overweight children participating in a multisite RCT.

METHODS

The Hunter Illawarra Kids Challenge Using Parent Support (HIKCUPS) study was a multisite RCT with 6- and 12-month follow-up. Study methods (17) and intervention effects on adiposity (23) and dietary behaviors (2) have been reported elsewhere. Briefly, the study was a three-arm, parallel group RCT conducted at the Universities of Wollongong and Newcastle, New South Wales, Australia. Participants were recruited from surrounding communities using advertisements in school newsletters and community newspapers, referrals from general practitioners, e-mails, and advertisements in local universities and hospitals. Eligibility criteria included the child being overweight or obese (referred to hereafter as overweight) according to International Obesity Task Force cut points (6), aged 5.5-9 yr, prepubertal (Tanner stage 1), and generally healthy. Exclusion criteria included extreme obesity (body mass index (BMI) z-score > 4), known syndromal obesity, a chronic illness, following a therapeutic diet, and taking medications associated with weight gain or long-term steroids. The human research ethics committees at both sites approved the study protocol. Written informed consent was obtained from each child's parent or caregiver as well as child assent.

Eligible participants were individually randomized to one of three intervention arms using a computer-based random number-producing algorithm: 1) a child-centered physical activity skill development program (PA), 2) a parent-centered dietary modification program (DIET), or 3) a combination of both programs (PA+DIET). Randomization was stratified by gender and site. To ensure concealment, the sequence was generated by a statistician and given to only one researcher at each site, who assigned participants to their groups and informed a member of the research team at each site, who enrolled participants, of group allocation. It was necessary to randomize participants before baseline assessments because families needed sufficient lead time to organize their work hours, transportation, and child minding to accommodate the intervention requirements. Sample size calculations for HIKCUPS were based on BMI z-score (primary outcome). Seventy-two participants in each of the three groups (216 in total) were required to be recruited to have an 80% chance of detecting as a statistically significant difference (at the two-sided 5% level) a 0.26 SD difference from baseline to 12 months in BMI z-score, with an anticipated loss to follow-up of 20%.

Physical activity skill development program.

The HIKCUPS physical activity program aimed to promote physical activity and to reduce time spent in recreational screen behaviors by fostering movement skill proficiency and by enhancing perceptions of physical competence through an educationally sound and socially supportive group program. The program was based on competence motivation theory (38), which posits that children are motivated to participate in physical activity if they enjoy it, perceive they can do it, have the actual underlying movement skills, and receive support from parents, instructors, and peers to participate. This theory was considered particularly relevant for physical activity promotion among overweight children because they exhibit poorer motor proficiency (21) and lower physical self-perceptions (10) than their leaner peers, which potentially contribute to their lower levels of physical activity (26).

The 6-month intervention was divided into two components: a 10-wk face-to-face program and a minimal-contact 3-month maintenance phase. The first phase of treatment included ten 2-h weekly group sessions (∼90 min of physical activity per session) and weekly "home challenge" activities. The intervention was refined from feasibility research (4) and was facilitated by two qualified teachers with expertise in physical education. Face-to-face sessions were administered to children after school at publicly accessible university gymnasiums, with parents participating in some activities in the first session and encouraged to complete skill development activities at home with their child each week. The sessions focused on developing children's proficiency in 12 fundamental movement skills, and learning experiences were designed to enable children to experience success and to improve perceived competence within a supportive environment. Movement skill development occurs in identifiable levels with associated stages (12). Sessions were therefore structured to cater for learners at the novice and intermediate levels and to incorporated the earliest learning stages of exploration, discovery, practice, and application (12). Each skill can be broken down into distinct performance components, which identify specific topographical aspects of the movement pattern. The presence or absence of these performance components can be used to identify children's transition through each skill's developmental stages, from immature to mature. Facilitators focused on detecting and correcting errors in movement skill technique and provided participants with skill-specific feedback by targeting each skill's performance components. Table 1 outlines the content and structure of the program and the example components for two movement skills.

TABLE 1
TABLE 1:
Session content and structure for the physical activity skill development program and example components for the hop and strike.

To promote physical activity and skill practice between sessions and to displace time spent in screen behaviors during the critical after-school window, each child completed activities as part of the "home challenge" program. These activities were modified from and reinforced program session activities; could be undertaken alone but preferably with parents, siblings, and/or friends; required minimal equipment; and involved a variety of activities that could be completed indoors or outdoors within limited space. Children and their parents were encouraged to complete a minimum of 30 min of home challenge tasks, three times per week during weeks 2-9. Parents recorded children's time spent completing home challenges each week, and a reward sticker chart and certificates were used as incentives to maximize adherence.

Parents attended a workshop during the last session of the 10-wk program designed to enhance their capacity to provide social support for physical activity to their children. During this session, strategies were discussed to target change and maintenance of children's physical activity, screen-based recreation, and movement skill proficiency. These included behavior monitoring, barrier identification, problem solving, planning, and goal setting. Parents set realistic short- to medium-term goals for increasing their child's physical activity and movement skill proficiency and for reducing sedentary behaviors. Progress toward goals was encouraged and assessed during the intervention maintenance phase (phase 2), which involved monthly follow-up telephone calls for 3 months. Telephone calls followed a standardized study protocol and assisted parents in problem-solving barriers to behavior change and devising new goals. In addition, the maintenance phase included a movement skill booster session with children 8 wk after the end of the initial 10-wk component. All 12 skills and their components were revised during this session, through revisiting activities completed during the face-to-face program, combined with facilitator instruction, questioning, and feedback.

Dietary modification program.

The dietary modification program was a parent-only intervention that aimed to improve food behaviors and diet quality and has been described in detail elsewhere (2). Government brochures detailing the Australian physical activity and electronic media recommendations for 5- to 12-yr-olds were provided to all groups at the start of the program, including the DIET group, to standardize the diet group's exposure to information for these nontargeted behaviors. Changes in children's physical activity and recreational screen behaviors were otherwise not targeted in the dietary modification program.

Combined physical activity and dietary modification program.

This group received identical versions of PA and DIET interventions, with parents and children participating concurrently. Intervention maintenance phase strategies for this group targeted physical activity, screen-based recreation, movement skill proficiency, and dietary modification.

Data collection.

Baseline assessments were taken after randomization, and all outcomes were measured using the same standardized protocols at 6- and 12-month follow-up. To identify the efficacy of the physical activity skill development program, changes in movement skill proficiency, perceived athletic competence, objectively measured physical activity, and screen behaviors, as described in the following sections, were assessed. Standardization of procedures and equipment were maintained across sites and cohorts by a mobile assessment team, identical study assessment protocols, and consistent assessor training.

Adiposity.

Height, weight, and waist circumference were measured using standardized procedures, which have been reported in detail (2,17). z-scores for BMI (kg·m−2) were calculated using UK reference data (7).

Movement skill proficiency.

The Test of Gross Motor Development, Second Edition (TGMD-2) (33) was used to assess change in children's fundamental movement skill proficiency. The TGMD-2 is comprised of six locomotor skills (run, gallop, hop, leap, horizontal jump, and slide) and six object-control skills (striking a stationary ball, stationary basketball dribble, catch, stationary kick, overhand throw, and underhand roll) and has established validity and reliability in children (33). The test was administered in small groups (≤4) following standardized procedures, instructions, and demonstrations. Children completed two trials of each skill, which were recorded using a digital video camera (Sony DCR2-HC52 Mini DV, Japan) to allow for greater measurement scrutiny. A single-blinded assessor scored the performance components (Table 1) of each skill as 1 (present) or 0 (absent) during each of the two trials. Scores for each trial were summed to give total skill scores, and skill scores in each of the two subscales were summed and converted to provide gender- and age-adjusted locomotor and object-control standard scores (33). Standard scores were summed and converted to calculate each child's gross motor quotient. Inter- and intra-assessor reliability were examined at baseline among 38 randomly selected participants. Assessor evaluations were compared against an independent criterion-assessor's evaluations and with repeat assessments completed 2 wk later. Reliability coefficients from two-way mixed-effect models were gross motor quotient (interclass correlation coefficient = 0.91, intraclass correlation coefficient = 0.89), locomotor (interclass correlation coefficient = 0.92, intraclass correlation coefficient = 0.90), and object control (interclass correlation coefficient = 0.81, intraclass correlation coefficient = 0.80).

Perceived athletic competence.

Perceived competence was assessed among 8- to 9-yr-olds using the Self-Perception Profile for Children (SPPC) (13) and among 5- to 7-yr-olds using the Pictorial Scale of Perceived Competence and Social Acceptance for Young Children (PSPCSA-YC) (14). Both questionnaires have established validity and reliability for the corresponding age ranges (13,14), with the PSPCSA-YC designed as an age-appropriate downward extension of the SPPC for younger children. The common domains of athletic competence (SPPC) and physical competence (PSPCSA-YC), both comprising six items, were combined to examine change in physical activity-related self-perceptions (hereafter called athletic competence) after treatment. This allowed for an examination of all participants and maximized statistical power. Participants completed the same questionnaire at all time points. Questionnaires were administered via a structured one-on-one interview by a blinded assessor. Items on both questionnaires used a structured-alternative format to minimize social desirability bias (13). For each item, participants chose which child they were most like from two options (high or low perceived competence) and whether this choice was "sort of true" or "really true" for them. Item scores range from 1 (low) to 4 (high) and were summed and averaged to provide the mean for analyses. Internal consistency reliability coefficients in this study were 0.71 for SPPC athletic and 0.62 for PSPCSA-YC physical.

Physical activity.

Habitual physical activity was measured using the ActiGraph 7164 uniaxial accelerometer (MTI Health Services, Fort Walton Beach, FL). Objective measures such as accelerometers overcome recall or reporting biases associated with child- or parent-proxy reports (29) and have rarely been used in pediatric obesity treatment studies (3). The ActiGraph 7164 has been validated against energy expenditure among children (29) and has detected change in children's activity in RCT (15,27,37). Participants wore the accelerometer on the right hip, as demonstrated and fitted by a trained and blinded assessor. Children were asked to wear the accelerometer during all waking hours over eight consecutive days, excluding aquatic activities. ActiGraphs recorded activity counts at 1-min epochs. Because of the memory capacity restrictions of this accelerometer, we needed to apply this sampling period to achieve a full 8 d of monitoring (26). Although a 1-min epoch may potentially underestimate children's sporadic moderate-to-vigorous physical activity (MVPA), consistent use of this sampling period across all groups at each assessment ensured that estimates of intervention effects were not biased. Parents and children recorded periods of nonwear physical activities undertaken during nonwear time (e.g., swimming) and activities that accelerometers inaccurately assess (e.g., cycling) on activity logs. Strings of ≥20 consecutive 0 counts were defined as nonwear time and removed during data reduction. Participant data were included in analyses if accelerometers were worn for ≥10 h·d−1 on ≥4 d (30). To minimize missing data at follow-up, children received inexpensive and self-selected prizes, such as pens and sticker sets, for meeting the compliance requirements, and parents received reminder telephone calls during the monitoring period. Participants' mean activity counts per minute of monitoring time was calculated and used in analyses as a measure of total physical activity. In addition, activity count thresholds were applied to the data using an age-specific energy expenditure prediction equation (11) to calculate time spent in moderate physical activity (MPA; 3.0-5.9 METs; from 6 yr, ≥614 and < 2972 counts, through 10 yr, ≥1017 and < 3696 counts), vigorous physical activity (VPA; >6.0 METs; from 6 yr, ≥2972 counts, through 10 yr, ≥3696 counts), and MVPA (>3.0 METs). This equation has acceptable predictive validity for the classification of differing intensities of activity (32). To account for differences in monitor wear time, the total minutes spent at each activity intensity were divided by the total minutes monitored to compute the percentage of time spent in MPA, VPA, and MVPA. An additional outcome, percentage of time in adjusted MVPA, was also computed using a standardized procedure described by Trost et al. (31) to examine whether adjusting minutes in MVPA for nonmonitored activities reported on logs altered study findings. Because children's activity patterns may differ on weekdays compared with weekend days, change in activity outcomes was also tested using only participant data that included at least one weekend day.

Screen behaviors.

The screen behaviors subscale of the Children's Leisure Activities Study Survey (28) was completed by parents to assess children's time spent in TV or DVD viewing, playing electronic games, and using the computer or the Internet for fun. Items for this subscale have been shown to have acceptable test-retest reliability (inter- and intraclass correlation coefficients ≥ 0.6) and convergent validity (28) and have been used in experimental research to examine changes in children's screen behaviors (27). Parents reported how much time (h, min) their child spent in each type of screen behavior during a typical week (Monday to Friday) and weekend (Saturday and Sunday) at each assessment time point. Weekday and weekend times were summed to calculate minutes per week in each of the screen-based behaviors and total weekly screen time.

Data and analysis.

The impact of group (DIET, PA, and PA+DIET), time (baseline, 6 months, and 12 months), and group × time interaction on the study outcomes was assessed using linear mixed models (5), with these three terms forming the base model. This approach was preferred to using baseline scores as covariates because the baseline scores for participants who dropped out at 6 months and/or 12 months were retained, consistent with an intention-to-treat analysis. Models were adjusted for any additional significant effects because of the main effects of covariates gender, location (two sites), and age (treated as continuous) and two-way interactions between time and group and these three covariates and the three-way interactions group × time × gender or location (but not age). Mixed models were fitted using the SAS PROC MIXED and REML estimation with an unstructured covariance structure and the Kenward-Roger adjustment for downward bias in the variance-covariance matrix. The effects of lack of normality and influential observations were evaluated but were not severe enough to impact the results. Differences of means and 95% confidence intervals were estimated using the mixed models, and statistical significance was set at P < 0.05. Differences between groups for process data were tested using chi-squared tests and t-tests.

RESULTS

Participant recruitment, flow, and baseline data.

Participants were recruited at each site from January 2005 to April 2006 as four cohorts commencing at the start of each school term in April, July, and October 2005 and April 2006. Six- and 12-month follow-up assessments for each cohort were conducted from September 2005 to September 2006 and from March 2006 to March 2007, respectively. The flow chart for enrolment, randomization, and follow-up of participants with BMI z-score as the HIKCUPS study primary outcome is shown in Figure 1. Of the 165 participants who completed height and weight assessments at baseline, 114 (69%) and 106 (64%) children completed these assessments at 6- and 12-month follow-up, respectively (Fig. 1).

FIGURE 1
FIGURE 1:
Flow of participants through the HIKCUPS trial and the number analyzed for the primary outcome (BMI z-score).

Useable physical activity data were collected from 137 children (83%) at baseline, 87 children (53%) at 6-month follow-up, and 79 children (48%) at 12-month follow-up. At baseline, at 6-month follow-up, and at 12-month follow-up, 17, 23, and 25 participants, respectively, did not meet the physical activity inclusion criteria and were excluded. Monitor malfunction occurred in 10 and 4 cases at baseline and at 6-month follow-up, respectively. The median (interquartile (IQ) range) number of days and minutes monitored per day at baseline, at 6 months, and at 12 months, respectively, were 7 d (7-8 d) and 757 min·d−1 (720-794 min·d−1), 7 d (5-7 d) and 757 min·d−1 (725-800 min·d−1), and 6 d (6-7 d) and 759 min·d−1 (719-807 min·d−1). Baseline descriptive data for the 165 participating overweight children (age = 8.2 ± 1.1 yr, 59% girls, BMI z-score = 2.8 ± 3.7, 78% obese) are reported in Table 2. Participants spent on average 194 min·d−1 in MVPA at baseline, 171 min·d−1 in total screen time, and had a mean gross motor quotient of 57.4 units, which placed them in the bottom <1% of children their age, according to the TGMD-2 normative US sample (33).

TABLE 2
TABLE 2:
Baseline characteristics of children randomized to the PA, DIET, and PA+DIET groups.

Movement skill proficiency and perceived athletic competence.

Improvements in movement skill proficiency at 6 months were greater in the PA and PA+DIET groups compared with DIET participants and were consistent across locomotor and object-control skill subscales (Table 3). The treatment effects equated to average gross motor quotient gains of approximately 11%-13%. A significant time effect for perceived athletic competence (P < 0.001) indicated that improvements were evident at 6 and 12 months for the total sample (mean (95% confidence interval) 6 months = +0.21 units (0.11-0.31 units), 12 months = +0.21 units (0.07-0.35 units)). Perceived athletic competence increased in both the PA and the PA+DIET groups at 6 months and in the PA+DIET group at 12 months, although the between-group differences were not statistically significant (Table 3).

TABLE 3
TABLE 3:
Change in movement skills and perceived athletic competence for treatment groups from baseline to 6 and 12 months.

Physical activity.

Nonsignificant group × time effects for all physical activity outcomes (all P > 0.05) indicated that the mean change did not differ between groups at follow-up (Table 4). Adjusting percent of time in MVPA for nonmonitored activities did not impact the between-group findings. Likewise, including only participant data with at least one weekend day also did not alter the conclusions for physical activity outcomes.

TABLE 4
TABLE 4:
Change in physical activity for treatment groups from baseline to 6 and 12 months.

Screen behaviors.

All intervention groups achieved statistically significant reductions in total screen time at 6 months, as did the activity and the activity + diet groups at 12 months, and no between-group differences were detected (Table 5). Declines in total screen time were predominantly the result of reductions in TV or DVD viewing and electronic game use. When all groups were combined, participants decreased their total screen time by an average of 55 and 39 min·d−1 and their TV or DVD viewing time by 32 and 18 min·d−1 at 6 and 12 months, respectively. Reductions in TV or DVD viewing time at 6 months were on average 35 min·d−1 greater in the DIET group compared with the PA group (Table 5).

TABLE 5
TABLE 5:
Change in screen behaviors for treatment groups from baseline to 6 and 12 months.

Process evaluation.

Process evaluation data examining intervention delivery and compliance have been reported elsewhere (18). Briefly, for the PA and PA+DIET programs, physical activity program deliverers reported implementing 98%-99% of scheduled activities. The agreement between evaluations by program deliverers and independent reviewers of delivered content ranged between 96% and 100%. For the PA, DIET, and PA+DIET programs, median (IQ range) attendance was 90% (70%-100%), 75% (40%-75%), and 90% (70%-90%), respectively. PA and PA+DIET participants spent over 1.5 h·wk−1 (median = 94 min·wk−1, IQ range = 66-124 min·wk−1) completing home challenge activities and were compliant for approximately 6 of the prescribed 8 wk (median = 75%, IQ = 38%-100%).

DISCUSSION

To our knowledge, this is the first RCT to examine the effects of a movement skill development physical activity program on behavioral and psychological outcomes among overweight children at 6 and 12 months. The consistent improvements across locomotor and object-control subdomains at 6 months for both the PA and the PA+DIET groups after a 3-month minimal-contact maintenance phase is evidence of this treatment's efficacy. Although statistically significant differences between groups were detected, data to assist with the interpretation of the clinical meaningfulness of these changes are not available.

Participating overweight children exhibited low movement skill proficiency at baseline, which is consistent with previous research demonstrating lower proficiency among overweight children compared with their nonoverweight peers (21). The treatment-seeking overweight sample in this study may have exhibited greater deficiencies in movement competency than are typical of overweight children because parents actively enrolled their children in this research, which was evaluating a physical activity skill development program. Video assessments also allowed greater measurement scrutiny than is common during live field assessments, and this may have contributed to the low levels of movement skill proficiency before treatment. In contrast, when compared with studies of overweight (15,37) and nonoverweight (27,31) children, participants in this trial had higher total physical activity levels and spent more time in MVPA at baseline than might be expected of overweight children. For example, a representative sample of grade 1-3 children in the United States who had their physical activity assessed using the same accelerometer and the same equation for categorizing MVPA as in the current study spent approximately 200 min·d−1 in MVPA (31), slightly more than the current sample at baseline. Cut points for MVPA derived from the equation of Freedson et al. (11) are lower than those used in some pediatric accelerometer studies (15,37), and this combined with the application of stringent accelerometer data reduction and inclusion criteria may have influenced physical activity outcomes in the current study.

Given participants' low movement skill proficiency at baseline, some might expect greater intervention effects than were observed in this trial at 6 or 12 months. One consideration is that 6-month follow-up data were collected after a 3-month maintenance phase, which potentially provides a conservative estimate of treatment effects. It is possible that, despite the application of intervention maintenance phase strategies designed to support parent and child autonomy of movement skill practice and physical activity participation, movement skill proficiency may have regressed toward baseline among PA and PA+DIET participants between the end of the face-to-face program and the 6-month assessment if practice was not sustained. Likewise, the intervention dose was approximately 90 min of face-to-face instruction and 60 min of additional practice for each of the 12 skills, if full compliance with home challenge activities was achieved. To obtain greater effects or to prevent the regression in movement skill proficiency that was observed among PA and PA+DIET participants between 6 and 12 months, the intervention dose may need to be of greater intensity or modifications may be required. These could include i) increasing the number of weekly face-to-face sessions or the program length, ii) reducing the number of skills and targeting those that best predict child physical activity behavior, or iii) focusing more explicitly on physical activity opportunities following the face-to-face program that support motor development.

Within-group improvements in perceived athletic competence following the activity and the activity + diet groups at 6 months and the activity + diet group at 12 months were similar to or greater than the changes reported following other obesity interventions (8,34). Perceived athletic competence also increased in the diet group at 6 months, and between-group differences were not significant. These findings suggest that causal associations between children's movement skill proficiency and perceptions of competence in the physical activity domain may be weaker than hypothesized, at least in the short term. Other factors that were targeted in this intervention but were not measured, such as social support (38), might also be influential in shaping children's physical activity-related self-perceptions. The minimal decline exhibited by the diet group is not indicative of expected developmental changes in untreated children (16) and may have been the result of enhanced parental support for weight-related behaviors, nonspecific treatment effects, random error, or regression to the mean.

A recent systematic review (3) found that two high-quality RCT have examined the effects of childhood obesity treatment interventions on physical activity using objective measures (15,37). Unlike these previous studies, no between-group differences were evident for physical activity outcomes in the current trial. The within-group effects of the PA AND PA+DIET treatments on total physical activity at 6 months were similar to or greater than the effects reported in previous trials (15,37). Whereas comparison groups in previous studies have, however, exhibited substantial declines in total physical activity over 6 months (15,37)-resulting in positive treatment effects in one trial (15)-total physical activity was largely maintained in the diet comparison group in this study. The minimal change exhibited by the diet participants may be due to the effective, family-centered intervention they received. That is, despite receiving treatment that explicitly targeted and achieved dietary and adiposity changes (2,23), parents of the children in the diet group may have supported physical activity participation because of their understanding of the role of physical activity in weight loss and because of their motivation to improve their child's weight status. Although data on participants' socioeconomic status were not available, the sample was possibly limited in cultural and socioeconomic diversity, as is typically found in the volunteer samples of child obesity treatment trials (24). If participating families were well educated, this may have influenced physical activity outcomes among diet participants. The higher than expected physical activity levels at baseline may also have created a "ceiling" effect, limiting the impact of treatment on physical activity. Although methodological protocols such as the data reduction procedures, the inclusion criteria, and the cut points used to categorize MVPA may have influenced estimates of physical activity outcomes, these procedures were consistent for all groups at all time points and are therefore unlikely to have altered study conclusions regarding differences between groups in changes in physical activity. Useable physical activity data were available for approximately half of the sample at follow-up, which potentially limit conclusions about the effects of the programs on physical activity. Although participant compliance with accelerometer assessments was similar to that found in another large-scale child obesity treatment trial (15), the missing data and the moderate loss to follow-up contributed to uncertainty in the findings, as indicated by the wide 95% confidence intervals.

The smaller than hypothesized impact on physical activity in this study may be because short-term changes in movement skill proficiency may not be causally related to physical activity in overweight children. Research suggests that motor development is positively related to physical activity among young people (1,22,40), including in a study of overweight children (20). However, evidence from experimental studies has not supported this relationship in preschool (25) and school-based (27) RCT. Movement skill proficiency may need to be developed and sustained over a longer duration to influence physical activity participation. Furthermore, a cross-sectional examination suggests that this relationship may be strongest at the uppermost quartile of motor proficiency (40). Because participants in the PA and PA+DIET groups remained below the 2nd percentile (categorized as "poor") for movement skill proficiency at 6 months (33), intervention effects were possibly not of the magnitude required to shift overweight children's movement skill proficiency above this influence threshold.

Similar to this study, several RCT have reported change in overweight and obese children's screen time or sedentary behavior after treatment (9,15). Unlike in the PA and PA+DIET groups, reductions in total screen time at 6 months among diet participants were not maintained at 12 months. The PA and the PA+DIET treatments targeted screen behaviors directly but briefly, through a single behavior-change session with parents, during maintenance phase telephone follow-up, and through displacement of screen behavior time during the critical after-school period with home-based physical activities. Supporting parents' efforts to modify their child's screen behaviors through these behavior-change strategies may have influenced the maintenance of improvements among PA and PA+DIET participants. The consistent reductions in screen behaviors for all groups at 6 months might be attributable to parents' understanding of the role of sedentary behavior in weight loss and because of their motivation to improve their child's weight status. In addition, parent-proxy reports were used to examine change in screen behaviors, which are vulnerable to reporting bias. Nonetheless, reported reductions in screen behaviors are substantiated by improvements in adiposity for all groups (23) and may therefore be indicative of actual behavior change.

Strengths of this study include i) assessment of key obesity-determining behaviors as well as the theoretical constructs targeted by the intervention, ii) recruitment of a moderately large and homogenous sample of overweight children, iii) blinded assessment of outcomes with 12-month follow-up, iv) process evaluation assessing intervention delivery and uptake (18), and v) analyses conducted according to the intention-to-treat principle. Furthermore, physical activity was objectively measured, which assisted in minimizing reporting bias. Likewise, movement skill proficiency was assessed from video by one blinded assessor who displayed adequate inter- and intraobserver reliability, using a validated tool that accounted for age and gender differences in motor development. The tested intervention was theoretically based and designed to be inexpensive, generalizable, and capable of being delivered in community settings by facilitators trained in pediatric physical activity promotion.

This study had several limitations. The DIET program was used as an active comparison group to examine change in movement skill proficiency, perceived competence, physical activity, and screen behaviors after the PA and PA+DIET programs. Improvements in diet (2) and adiposity (23) in the DIET group at 6 and 12 months suggest that participants might not have been representative of untreated overweight children. Inclusion of a no-treatment control group would have demonstrated intervention effects more clearly. However, the ethical concerns associated with such a group and the likely lack of acceptability to parents and children of being allocated to this group in an obesity treatment trial with a 12-month follow-up might have influenced retention rates and reduced internal validity (36). Posttest data were collected after a 3-month maintenance phase to examine the sustainability of treatment effects, but these estimates might be conservative. Effects on physical activity and other outcomes may have been most prominent immediately after the face-to-face programs. The wide 95% confidence intervals for physical activity outcomes and perceived athletic competence suggest that the sample size was inadequate and the analyses were underpowered.

In conclusion, the physical activity skill development program, alone or combined, resulted in short-term improvements in movement skills. The combined program exhibited the greatest within-group improvements in perceived athletic competence. Time in screen behaviors was reduced in all groups, although the impact on physical activity was small and less clear. Factors in addition to improved movement skill proficiency may be needed to increase overweight children's physical activity. Because the combined PA+DIET program resulted in improved adiposity (23), dietary intake (2), movement skills, perceptions of athletic competence, and screen behaviors among overweight children, effectiveness trials are recommended to assess whether intervention outcomes can be achieved when delivered by health professionals in community settings.

This project was funded by the National Health and Medical Research Council of Australia (grant 354101), and this was their sole contribution to the study.

The authors thank the participating children and parents, the local schools in the Hunter and Illawarra regions of New South Wales, and the Universities of Wollongong and Newcastle. They also thank the Health Food Company Sanitarium for supplying breakfast cereal for the children's postfasting assessments.

Conflict of interest: The authors declare no conflict of interest.

Trial registration: clinical trials.gov; identifier: NCT00107692.

The results of the present study do not constitute endorsement by the American College of Sports Medicine.

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Keywords:

EXERCISE; INTERVENTION; MOTOR SKILL; OVERWEIGHT; SEDENTARY BEHAVIOR

©2011The American College of Sports Medicine