The Effect of Peer Influence on the Amount of Physical Activity Performed in 8- to 12-Year-Old Boys

Abstract

The purpose of this study was to determine the amount of physical and sedentary activity normal-weight and at-risk-for/overweight boys perform when alone, with a peer of similar weight and with a peer of different weight. Participants included boys, ages 8–12 years, classified as either normal-weight (<85th BMI percentile; N = 12) or at-risk-for/overweight (<85th BMI percentile; N = 12). At-risk-for/overweight boys allocated a greater amount of time to sedentary activities and accumulated fewer accelerometer counts than normal-weight boys in the alone condition. Once paired with a peer of either similar or different weight there were no differences between groups. These results indicate the presence of an unknown peer has a positive effect on at-risk-for/overweight children’s physical activity behavior.

Regular participation in physical activity during childhood and adolescence increases self-esteem, promotes increases in bone mineral density, muscular strength and endurance and aerobic fitness (5,7,26). In addition, multiple studies have indicated that the amount of physical activity a child participates in is inversely associated with of the development of childhood obesity (2,14,20,27,32,35,49). However, there is evidence that the majority of children do not participate in adequate amounts of physical activity at moderate or vigorous intensities (1,31). Because youth are not participating in adequate amounts of physical activity and because this lack of participation leads to negative health consequences, it is important to develop a better understanding of the factors influencing physical activity behavior in children. This greater understanding may eventually lead to the development of more effective exercise interventions and recommendations for children.

There is emerging evidence that children’s social network may be uniquely relevant and influential to their choice of activities (13,24,33,40,42). Normal-weight and overweight children have been found to be more physically active in the presence of peers and friends in their natural environment than when alone or in the presence of family members (40). However, in an organized setting, such as gym class or a sport team, overweight children have been reported to be less physically active when in the presence of their peers (33,39). It has been hypothesized that overweight children face peer rejection in these organized settings and as a result withdraw from the activity (10,22,23). Therefore, weight criticism and peer victimization may influence children to withdraw from organized physically active settings involving peers, such as sport teams, and allocate more time to solitary activities that tend to be sedentary in nature (38,44,49). The differential effects of peer influence on children’s physical activity in organized and unorganized settings may be influenced by the types of peers present during these activities (36,37,40). It has been proposed that in an organized setting where overweight children interact with normal-weight children; overweight children are often ridiculed, thus reducing their desire to participate in physical activity (12,40). Children tend to befriend peers who are similar to themselves and overweight children affiliate with other overweight children to avoid weight criticism (6,8,9). This may increase overweight children’s willingness to be physically active with a similar peer. It could also partially explain why overweight children appear to be more active with peers in an unstructured setting, where peers are likely friends of similar weight, while avoiding physical activity with peers in an organized setting, where peers are not necessarily friends and are more likely different in weight. However, no previous study has directly observed the impact of a peer’s weight status on a child’s physical activity behavior.

Previous studies on peer influence on physical activity behavior have mostly relied on children’s self-report data (3,4,33,40,49). The authors are only aware of a single controlled laboratory study examining the impact peers on children’s physical activity patterns (41). These results showed that both normal-weight and at-risk-for/overweight children increased their physical activity in the presence of a friend, but only at-risk-for/overweight children did so in the presence of an unknown peer. This previous study used a cycle ergometer as the only available physical activity option. This activity is likely different from the activities children typically encounter in their natural environment. Another limitation of this previous study was that the impact of the peers’ weight status (friends and non friends) was not reported.

This study assesses at-risk-for/overweight and normal-weight boys’ physical activity as a function of three social conditions: alone, with a peer of similar weight and with a peer of different weight. In each of these conditions children had access to a variety of age appropriate physical activities and sedentary alternatives. Children’s actual physical activity, their liking (enjoyment) of physical activity as well as their time allocation to sedentary alternatives were the important dependent variables measured. The present study is novel in that physical activity was assessed in a more naturalistic environment than the one used in previous studies (e.g., a gymnasium with multiple physical activity options versus a single cycle ergometer) and that the effect of the peer’s weight status was examined.

Based on previous work on the impact of the social context on physical activity we hypothesized that at-risk-for/overweight children would be less physically active than normal weight children when alone, but that the presence of a peer would increase their physical activity and eliminate the difference in physical activity between at-risk-for/overweight and normal weight children (41). We also hypothesized that the with-peer increases in physical activity for the at-risk-for/overweight children would be greatest when peers were of similar weight. Previous controlled research examining the impact of peer influence of physical activity demonstrated that normal-weight children only increased physical activity behavior in the presence of a friend. In the current study children were paired with unknown peers only. Therefore, we hypothesized that normal-weight children would not increase physical activity in either with-peer condition.

Methods and Research Design

Methods

Participants.

Participants were boys (N = 24), age 8–12 years who were classified as either normal-weight (<85th BMI percentile; N = 12 all Caucasian) or at-risk-for/overweight (<85th BMI percentile; N = 12, N = 11 Caucasian, N = 1 African American). The children were recruited from the local community through flyers and through a database of subjects who had previously contacted the Applied Physiology Laboratory to participate in previous, unrelated research projects. Children were excluded from participating in the study if they had any conditions that limited their ability to participate in, or any contraindications to, physical activity, including; BMI for age less than the 5th percentile, cardiovascular disease, neuromotor or cognitive disorders interfering with participation in physical activity.

Design

The study was a two group (normal-weight, at-risk-for/overweight) by three social condition (alone, with similar weight peer, with different weight peer) mixed design with group serving as the between subjects variable and social condition serving as the within subjects variable. The three social condition trials are as follows: One, activity alone: the participant had free-choice access to a variety of physical and sedentary activities for a period of 30 min with no other children present. Two, activity with a similar-weight peer: two participants of similar-weight (both children were normal weight or both children were at-risk-for/overweight) had free-choice access to a variety of physical and sedentary activities for a period of 30 min. Three, activity with a different-weight peer: two participants of different-weight (one normal weight participant with one at-risk-for/overweight participant) had free-choice access to a variety of physical and sedentary activities for a period of 30 min. Overall, there were six possible orders for completing the three social conditions and two subjects from each group underwent each possible order for complete counterbalancing.

Procedures

Eligibility of interested children was determined via phone screen with a parent or legal guardian. If children were eligible they were required to report to the Applied Physiology Laboratory at Kent State University for three separate visits. During the first visit, the child’s parent or legal guardian signed a consent form and the child signed an assent form. Children were then measured for height, with a stadiometer (Health O Meter, Chicago, Illinois) and weight, using a calibrated balance beam scale (Health O Meter, Chicago, Illinois). After anthropometric measures were completed children were taken into a 4,360 square foot gymnasium where a trained exercise physiologist demonstrated the physical activity options the children had access to. The activities included; one foot (0.305 m) tall modified hurdles, ski jump, jump rope, Nerf footballs and flying discs (Hasbro, Pawtucket, Rhode Island), standing long jump, kicking a soccer ball around a series of seven cones, and shooting a basketball at a standard 10 ft (3.05 m) hoop. Once the child sampled all seven activities they verbally acknowledged an understanding of how to use each of the following sedentary activities; drawing, crossword puzzles, word finds, magazines and the matching game Perfection (Milton Bradley Company, East Longmeadow Massachusetts). These sedentary options were located at a table with two chairs in the same gymnasium as the physical activity options.

After sampling the physical and sedentary activities, children participated in their first of three social condition trials either alone, with similar weight peer or with a different weight peer. During each of these conditions children had access to all of the physical and sedentary activities for a period of 30 min and their behavior was monitored by an experimenter who was present in the gymnasium. Children had the option to use any of the physical activities, run or walk around the gymnasium space as well as use any of the sedentary options or sit and rest on the chairs at the table with the sedentary activities. During visits two and three, which were conducted on separate days, children completed the remaining two social condition trials based upon predetermined counterbalancing orders. After each 30 min session, the liking, or hedonics, for that session was assessed using a visual analog scale (VAS) consisting of a 10 cm line anchored by ‘do not like it at all’ on the left side and ‘like it very much’ on the right side (29,36).

The amount and intensity of the physical activity each child performed was measured via accelerometery (ActiGraph GT1M, Pensacola FL) during each 30-min condition. The amount of time from each 30-min session that children allocated for participating in physical activities and sedentary activities was recorded utilizing a stop watch (Traceable Stopwatch, Fisher Scientific, Waltham, Massachusetts). At the conclusion of the third laboratory visit, children were compensated with a $30.00 gift certificate to a store of their choosing. All procedures were approved by the Institutional Review Board at Kent State University.

Measurements

Liking via visual analog scale (VAS): Children rated their liking using visual analog scales (VAS) consisting of a 10 cm line anchored by ‘do not like it at all’ on the left side and ‘like it very much’ on the right side. The ratings were made immediately following the final minute of each 30-min gymnasium session. Assessments of liking, or hedonics, are affective ratings of a behavior that directly correlate with physical activity participation (11,29,36). The specific scale used in the present investigation successfully predicts physical activity behavior in 8–12 year old children (36).

Accelerometer: The ActiGraph GT1M Monitor (ActiGraph, Pensacola, Florida) was worn at the children’s hip, snug against the body for the entirety of each 30-min gymnasium session. Epoch length was set at 60 s and the average per-minute counts were summed over each 30-min social condition to provide the measure of total physical activity per condition. The ActiGraph has been shown to be a valid and reliable tool for quantifying physical activity in children and adolescents (37).

Statistical Analysis

One way analysis of variance (ANOVA) were performed to examine differences in subject characteristics (age, height, weight, and BMI percentile) between groups (at-risk-for/overweight, normal-weight).

Mixed-effects models provide a useful approach to account for interdependence in multiple observations within individuals (19,24). Mixed models assume that the data within subjects are dependent among the observations. The outcomes at the individual level are modeled taking into consideration the dependence of observations within groups and individuals. All mixed-models were performed using SAS Software (43).

Physical Activity, Sedentary Time and Physical Activity Liking.

Mixed effects models were used to analyze the relationship between the dependent variables and the time variant (i.e., social condition) and time invariant predictors (weight status) and interactions between these terms.

The social conditions were dummy-coded as either 0 or 1 into three variables: alone, sim (similar weight peer) and dif (different weight peer). For the first models two of the social variables (alone and sim) were entered into the regression model and compared with the reference group (dif), which was left out of the model. However, because youth did not differ in terms of their activity counts in the two social conditions (dif and sim) we combined the social conditions and compared the effect of the presence of a peer to being alone. For the subsequent models, “alone” was entered into the regression models and compared with “dif” and “sim”, which were left out of the models. Our models predicting physical activity, time engage in sedentary activities and liking for physical activity are illustrated below:

$$\begin{gathered} \text{Accelerometer counts}=\alpha +\beta (\text{weight status})+\beta 2(\text{social condition})+\beta 3 \\ (\text{social condition}{}^{\ast }\text{weight status})+\beta 4(\text{PRS scores}) \end{gathered}$$

$$\begin{gathered} \text{Sedentary time}=\alpha +\beta 1(\text{weight status})+\beta 2(\text{social condition})+\beta 3(\text{social} \\ \text{condition}{}^{\ast }\text{weight status})+\beta 4(\text{PRS scores}) \end{gathered}$$

$$\begin{gathered} \text{Liking of physical activity}=\alpha +\beta 1(\text{weight status})+\beta 2(\text{social condition})+ \\ \beta 3(\text{social condition}{}^{\ast }\text{weight status})+\beta 4(\text{PRS scores}) \end{gathered}$$

Results

Individual Characteristics

Subject physical characteristics are shown in Table 1. The at-risk-for/overweight boys were significantly greater than normal-weight boys for height, weight, and BMI for age percentile (p ≤ .04 for all).

Table 1.

Subject Characteristics

	Normal-weight (N = 12)	Overweight (N = 12)
Age (years)	10.0 ± 1.4	10.8 ± 1.6
Height (cm)*	138.6 ± 9.9	147.6 ± 9.6
Weight (kg)*	33.2 ± 6.2	56.8 ± 17.1
BMI for age percentile*	54.6 ± 16.6	93.4 ± 6.0

Data are mean ± SD

^*Significant difference between groups (p ≤ 0.04).

Activity Counts

Findings on the model testing the effect of the social condition on children’s activity counts indicated an interaction of social condition by weight status, β = 33705 (95% CI: 9409–58000), p < .01 (Figure 1). Difference of least square means revealed that normal-weight boys were more physically active then at-risk-for/overweight boys when alone p < .05 but that this difference was no longer statistically significant when youth were in the presence of a peer, p = .6. Normal-weight boys were more physically active when alone, M = 136736, SD = 45623, then when in the presence of a peer, M = 109665, SD = 38133; p < .01; whereas overweight boys were more physically active when in the presence of a peer, M = 98521, SD = 21345, compared with being alone, M = 90332, SD = 38450, albeit this difference was not statistically significant (p = .3).

Figure 1 — Accelerometer Counts.

Significant group by condition interaction (p < .01) *At-risk-for/overweight children were less active (p < .01) than normal-weight when alone and not different (p = .6) in the other conditions.

Sedentary Time

Findings on the model testing the effect of the social condition on time children spent engaging in sedentary activity revealed a significant interaction of social condition by weight status, β = −5.32 (95% CI: −9.46—−1.18), p < .05 (Figure 2). Difference of least square means revealed that at-risk-for/overweight boys allocated significantly greater amounts of time to sedentary activities than normal-weight boys when alone p < .01 but that this difference was no longer statistically significant when youth were in the presence of a peer, p = .6. Normal-weight boys did not alter their sedentary activity time when alone, M = 1, SD = 4, versus with a peer, M = 2, SD = 6; p = .8; whereas at-risk-for/overweight boys participated in significantly less sedentary activity when in the presence of a peer, M = 3, SD = 3, compared with being alone, M = 8, SD = 7; p < .01.

Figure 2 — Sedentary Activity Time.

Significant group x condition interaction (p < .05) *At-risk-for/overweight children allocated greater amounts of time to sedentary activities (p < .01) than normal-weight when alone and were not different (p = .6) in the other conditions.

Liking of Physical Activity

Findings indicated an interaction of social condition by weight status, β = 1.02 (95% CI: −0.15–1.9) p = .05 (Figure 3). Overweight/obese participants demonstrated an increased liking for physical activity in the presence of a peer (M = 9, SD = 1) compared with when they were active alone (M = 8, SD = 2; p < .05); whereas nonoverweight youth reported liking physical activity equally when alone (M = 8, SD = 2) and when in the presence of a peer (M = 8, SD = 3; p = .9).

Figure 3 — Liking.

Significant group x condition interaction (p = .05) *At-risk-for/over-weight children significantly increased liking from the alone condition to the with-peer conditions (p < .05), there were no changes for normal-weight children (p = .90).

Discussion

This study examined the influence of peers and peers’ weight status on normal-weight and at-risk-for/overweight boys’ physical activity. Consistent with previous research, at-risk-for/overweight boys were less physically active than normal-weight children when alone. However, at-risk-for/overweight children increased their physical activity behavior in the presence of an unknown peer relative to the alone condition. This finding was further reinforced by the sedentary time data which indicated that at-risk-for/overweight boys spent less time engaged in sedentary activities when in the presence of a peer than when alone.

The accelerometer counts data were somewhat different from our expectations in that normal-weight boys’ physical activity actually decreased in the presence of a peer relative to the alone condition. Although these results appear surprising, this decrease in activity is likely due to boys sharing the activities with their peers. Based on accelerometer counts and the amount of time allocated to sedentary activity in the alone condition it seems that normal-weight children were physically active at a greater rate than at-risk-for/overweight children. Once normal-weight children were paired with another child they slowed their rate of physical activity to interact with their peer and take turns participating in the various physical activity stations. At-risk-for/overweight children also took turns and interacted when paired with peers but this did not reduce their rate of physical activity participation as their rate was much lower than that of a normal-weight child when alone. Because normal-weight children, unlike their at-risk-for/overweight counterparts, were active at such a great rate when alone and time was fixed at 30 min, they had little room for increases in physical activity in the with-peer social conditions. Extending or eliminating this time limit would have provided more of an opportunity for both groups of children to increase their physical activity participation in the with-peer conditions. Therefore, limiting the time in each social condition to 30 min may be a limitation of this study.

While the presence of a peer may not have significantly increased accelerometer counts for either group of children the significant reduction in sedentary time for at-risk-for/overweight children may be just as important. Increased sedentary behavior is associated with another obesogenic behavior; increased energy intake or snacking (15,16,42). If a child is alone for large amounts of time they are more likely to be sedentary and as a result, may increase snacking (15,16,42). Presently the presence of a peer reduced sedentary behavior for at-risk-for/overweight children. In previous studies which manipulated sedentary behavior, decreasing sedentary behavior successfully decreased energy intake in children (15,16). Therefore, if overweight youth spend less time engaged in sedentary behavior while in the presence of peers, it is possible that the presence of peers also result in a reduction in snacking. Future research examining the importance of the presence of a peer to reduce sedentary behavior and other obesigenic behaviors co-occurring while children are sedentary, (e.g., snacking), is warranted.

Interestingly, the presence of a peer also increased liking of physical activity in at-risk-for/overweight children. It is not clear why this did not occur in normal-weight children but there are some possible explanations. First, it is possible that at-risk-for/overweight children spend more time alone than their normal-weight peers (22,39,40,46). As a result, overweight youth might have a greater appreciation for the presence of peer than normal-weight children. Second, at-risk-for/over-weight children are more victimized during physical activity than normal-weight children and this is associated with a reduction in physical activity enjoyment (13,17,22,28,38,49). In the current study there was no overt criticism between children. The ability to interact with a peer in a physically active setting which was free of criticism may have contributed to the increased enjoyment of the at-risk-for/overweight children.

Because children are likely to befriend peers who are similar to themselves we had hypothesized that engaging in physical activity with similar weight peers would elicit the greatest increase in physical activity (6,8,9). However, peers’ weight status had no apparent effect on accelerometer counts, sedentary activity time or liking. At-risk-for/overweight children decreased sedentary activity, increased liking and, while not significant, increased accelerometer counts in the presence of an unknown peer regardless of that peers weight. This would suggest that interacting with peers, regardless of the weight of the peers, may be of importance if attempting to increase physical activity and decreasing sedentary behavior in at-risk-for/overweight child.

This study was not without limitations. First, these results are limited to boys only. Future investigations should examine girls as they may respond differently to the various with and without peer social conditions employed in the current study. In addition, as mentioned previously, children were limited to 30-min activity sessions, which may have limited the amount of physical activity they participated in. It would be interesting to determine if children would have been physically active for a longer period of time with peers than alone if no time limit were given. Future investigations should consider extending or eliminating the activity session time limit. This may result in greater fluctuations in physical activity from the alone to the with-peer social conditions.

In conclusion, the current study was only the second we are aware of, to assess the effect of peer influence on children’s physical activity behavior in a controlled environment (41). This study was novel in that it was first to evaluate the effect of the presence or absence of peers of similar and different weight on the physical activity behavior of normal-weight and at-risk-for/overweight children in a controlled environment using objective measures to assess activity. At-risk-for/overweight children accumulated fewer physical activity counts and allocated more time to sedentary activity than normal-weight children when alone with no differences between groups when in either of the with-peer conditions. At-risk-for/overweight children also significantly increased their liking in the with-peer conditions versus the alone condition whereas liking did not change in normal-weight children. Taken together these results suggest that the presence of a peer may reduce sedentary behavior and increase the enjoyment of physical activity in at-risk-for/overweight children. Additional research focusing on girls and perhaps extending the activity session time limits beyond 30 min is suggested.