Physical Activity in Urban School-Aged Children With Asthma

Setting and Sample

This cross-sectional study was conducted in the Harriet Lane Pediatric Clinic, an urban, hospital-based primary care pediatric clinic in Baltimore, Maryland. The accessible population was defined (using billing records) as any clinic enrollee 6 to 12 years old who had made a visit to the primary care clinic in the preceding 2 years (n = 3001). From this group, we selected a sample of children with asthma and randomly selected a sample of age-matched controls. To ensure an adequate number of subjects with asthma, we attempted to recruit any child who had a visit to our clinic or pediatric emergency department resulting in an asthma diagnosis (International Classification of Diseases, Ninth Revision code 493; n = 357). The asthma diagnosis would be confirmed later by interview, and children without asthma would still be eligible as controls.

Parents of all potential asthma subjects were sent a letter introducing the study and including a preaddressed and stamped reply card. Recipients were instructed to return the card if they wished to refuse participation or if they had a corrected telephone number. If the parent did not return the card and the letter was not returned by the post office as undeliverable, it was considered acceptable to telephone the family. An additional 357 subjects were selected randomly from an age-stratified list of the remaining 2644 children and contacted in the same manner as the asthma subjects (Fig 1).

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Fig 1.

Subject recruitment and disposition.

The combined list was sorted by using computer-assigned random numbers. The parents were phoned in order and asked to participate in the interview with the child available. At least 1 attempt was made to contact the caregiver of all potential subjects. Multiple repeat attempts were made until the interview was completed, the respondent declined participation, or the study period ended. When phone numbers were not in service, reattempts were made if an alternative phone number was available from other hospital records. Families were offered an incentive of 5 dollars for participation in the interview. Interviews were conducted between the beginning of the school year and the beginning of winter break (late August and mid-December) of 2001. The time period was chosen to limit the effect of seasonal variation on physical activity.

Exclusion Criteria

Exclusion criteria were evaluated by interview and included medical conditions that would modify physical activity: sickle cell disease, cystic fibrosis, diabetes, cerebral palsy, stroke, neuromuscular problems that affect walking, or any condition that requires use of a wheelchair or walker. Any children who had recent injury or illness that made them temporarily unable to do their usual types of activity or who had been to the emergency department or clinic for an asthma attack in the past 2 weeks were deferred for reinterview after 6 weeks.

Data Collection

A structured, 76-item questionnaire was administered by telephone interview by 1 of the investigators (D.M.L.) or 1 of 2 trained interviewers to caregivers addressing physical activity; sociodemographic factors; asthma diagnosis, symptoms, and medications; physician advice; parental health beliefs; and community resources and neighborhood safety. Interviewers were blinded to the asthma status at recruitment but would know the child’s asthma status from responses to the questionnaire.

Demographic items included the child’s age, gender, and insurance type and caregiver’s age and education. We attempted to obtain weights and heights from parent recall but found that 44% of caregivers could not give a precise response.

An asthma case was defined by using the criteria established by the Centers for Disease Control and Prevention in surveillance.²⁵ A child was considered to have asthma if a medical provider had ever diagnosed him or her with asthma and if the child had had some asthma symptom in the past 12 months. A child was considered not to have asthma if the parent was never told that the child had asthma. Asthma severity classification used the 4 steps of the National Asthma Education and Prevention Program guidelines using reported frequency of day and night symptoms in the past month.²⁶ Parents were asked to list all asthma medications that the child was using currently. Controller medication was defined as any inhaled mast-cell stabilizer, inhaled steroid, long-acting β-agonist, or leukotriene modifier; rescue medication was defined as any short-acting β-agonist.

Physical activity was measured in 2 ways: total minutes active on 1 day and the number of days active in a typical week. Only 1 recent day’s activity was measured because of concerns about recall of specific activities over longer periods.²⁷ The preferred day of interest was the previous day, but parents were given the option to use 1 day earlier if the previous day was not typical for the child. To assist in recall, the parent was asked how many minutes the child spent on each of a list of specific activities. The checklist concept was based on the “Yesterday Activity Checklist” of the Physical Activity Checklist Interview Protocol,²⁸ with the specific activities used in this study chosen after discussion with parents of children in our community. The list included sports, active games, and individual activities such as walking, running, and skating. The parent could add unlisted activities. To improve accuracy of recall, the parent was asked to have the child present for the interview so he or she could also be asked the questions. The physical activity interview was pilot tested for same-day test-retest reliability on a sample of 22 volunteer parents from a local elementary school by administering the same 30-minute interview twice.²⁹ In the pilot study, intraclass correlation for total minutes of activity was 0.97, and variability was 55%. Intraclass correlation for days per week active was 0.83, and variability was 31%. Internal validity evaluation showed more total minutes activity among children whose parents thought the child was “more active” than children whose parents thought the child was “less active” (P = .07) and among children who were reported active more days of the week (P = .05). The typical days per week was simply a number of days on which the child did strenuous activity.³⁰

Parents were asked whether the child’s doctor had ever spoken about exercise and whether the advice supported or discouraged exercise. Health beliefs were assessed by using a list of statements that address the benefit of exercise in general, the appropriateness of exercise in children with asthma, and the parent’s feelings about exercise in his or her child, with responses on a 5-point Likert-type scale: “strongly disagree,” “disagree,” “no opinion,” “agree,” and “strongly agree.”

Parents were asked whether the family lived within walking distance of a recreation center or a park and whether an adult exercised with the child. Neighborhood safety was assessed by agreement with the statement: “There is a safe place for my child to get exercise in my neighborhood.”

Sample Size

The desired sample size of 250 (150 with asthma and 100 controls) was calculated to provide a significance level of .05 and a power of .80³¹ to detect a hypothesized 25% difference in mean total minutes of physical activity and a 15% absolute difference in proportion of children with and without asthma active <30 minutes/day. More children with asthma were sampled to evaluate the relationship between predictive factors and physical activity level.

Analysis

The mean total daily minutes of physical activity, proportion of children active for <30 minutes/day, and proportion of children active <3 days/week were compared by asthma study group. Demographic characteristics and parental health beliefs also were compared in the 2 groups. The strength of association between predictive factors and physical activity then was analyzed in the children with asthma. For this analysis, total minutes of physical activity were collapsed into low (<30 minutes), medium (30–119 minutes), and high (≥120 minutes) to increase statistical power. The low of <30 minutes of activity was chosen to place the findings in context of national recommendations.³² Prediction of low activity versus all others and high activity versus all others were analyzed separately for each predictor by comparing percentages using χ² tests or calculating odds ratios (ORs) via univariate logistic regression. For each activity group, a multivariate logistic regression model with ORs was developed by using a stepwise approach by first including any predictor that was associated with activity at a significance level of at least P < .10 in the univariate analysis and then excluding from the final model any variable that did not reach a significance level of P < .05. Finally, a multinomial regression compared relative risk of inclusion in the highest activity group versus the lowest activity group, using the factors identified in the multivariate regressions. Data were analyzed by using Stata 7.0 (Stata Corporation, College Station, TX).

Institutional Review

This study was approved by the Johns Hopkins University School of Medicine Institutional Review Board. The recruitment of parent volunteers in the pilot study was also approved by the Baltimore City Public Schools Research and Evaluation Accountability Officer.

Asthma Versus Nonasthma

Children with asthma were less active than their peers, based on 3 activity criteria. The mean activity on 1 day was 116 minutes for children with asthma and 146 minutes for children without asthma (P < .05). Children with asthma were more likely to be inactive, defined as <30 minutes of activity per day (21% of children with asthma versus 9% of controls [P = .01]) or <3 days activity in a typical week (23% vs 11% [P < .05]). There was not a difference, however, in the proportion of children who were highly active, defined as ≥120 minutes of activity per day (47% vs 56% [P > .20]).

Physical Activity in Children With Asthma

Comparison of inactive versus active children with asthma revealed that low physical activity was strongly associated with reported symptom frequency but was not associated with use of controller medications, parent recall of physician advice concerning exercise, neighborhood safety, or access to recreation sites (Table 2). Disease severity was the only nonhealth belief associated with the highest activity level: 34% of the children with asthma who were active at least 120 minutes/day had moderate or severe persistent disease, compared with 56% who were active <120 minutes (P = .01).

Parental Health Beliefs and Activity

Table 3 lists the frequency of health beliefs among parents of children with asthma and controls. Some health beliefs were held by only a few or almost all parents, whereas others had considerable proportions of parents in each category.

Children with asthma whose parents feared that the child would get sick from exercise and those whose parents believed that the child got upset from strenuous play were more likely to be inactive. Alternatively, children whose parents believed the child could do as much activity as peers were less likely to be inactive (Table 4). In multivariate regression, 2 factors significantly predicted that a child with asthma would be active <30 minutes/day: moderate or severe persistent asthma and parental belief that the child gets upset with strenuous activity (Table 5). Female gender was significant as a univariate predictor of low activity but only borderline (P = .05) in the multivariate regression.

Children with asthma who enjoyed physical activity, those whose parents believed that they could do as much activity as their peers, and those whose parents believed exercise may make the child’s asthma better were more likely to be active at least 120 minutes/day. Alternatively, those whose parents reported that the child got upset with strenuous activity were less likely to be in this most active group (Table 4). On multivariate analysis, agreement that exercise may make the asthma better predicted >120 minutes of activity/day, whereas moderate or severe disease predicted <120 minutes of activity/day (Table 6).

In a final multinomial model, high activity (≥120 minutes) was less likely than low activity (<30 minutes) in children with moderate or severe persistent disease (relative risk ratio [RRR]: 0.26; confidence interval [CI]: 0.09–0.74), female gender (RRR: 0.35; CI: 0.13–0.98), and whose parents agreed that the child gets upset when he or she plays or exercises hard (RRR: 0.27; CI: 0.09–0.80). Agreement that exercise may make the child’s asthma better was associated with the high-activity group (RRR: 2.86; CI: 0.94–8.75), but the significance level was 0.06.