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Epidemiology

Age-related differences in physical activity levels of young adults

LESLIE, EVA; FOTHERINGHAM, MICHAEL J.; OWEN, NEVILLE; BAUMAN, ADRIAN

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Medicine and Science in Sports and Exercise: February 2001 - Volume 33 - Issue 2 - p 255-258
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Abstract

Physical activity levels of males and females decrease during the teenage years and young adulthood, while the prevalence of inactivity rises. Declines are observed in light-moderate activity and in vigorous activity in males and females between the ages of 12 and 21 yr (12). Data from cross-sectional and prospective studies indicates that the decline in physical activity is steepest between the ages of 13 and 18 yr (10). Prevalence rates reported for vigorous activity are higher among males than females, with females showing a decline at an earlier age than do males (12). Although the decline in physical activity is generally greater for males than for females, males are more active overall (10). Adult population surveys from Australia and other industrialized countries report declines in physical activity through young adulthood and beyond (1,8). In pooled Australian population data, the reported prevalence of “sedentariness” was 14% for those aged less than 25 yr and 24% for those aged 25–39 yr (8).

The planning and implementation of effective public health physical activity strategy can be influenced by a more-detailed understanding of the decreases in physical activity seen with age. The broader age group categories (often 10 or more yr) that have generally been reported for population surveys (1,4,8,12) do not provide a perspective on age-specific prevalences and trends within the early years of adulthood. During this period, significant changes in life circumstances may be strongly influencing physical activity patterns. In particular, the patterns for the years around the time of finishing school and either entering the workforce or starting tertiary studies have not been documented, nor have the patterns between the early adult years (where individuals are often gaining increased independence), and later phases of young adulthood when other responsibilities may impinge on discretionary time use.

We examined the relationship between reported leisure-time physical activity and age, for young adults aged between 18 and 29 yr, in three recent Australian surveys. Trend data for males and females in vigorous and moderate-intensity activity, walking and physical activity sufficient for health benefits across three age bands (18–19 yr, 20–24 yr, and 25–29 yr) are reported.

METHODS

Surveys and measures.

The data used for this study came from three separate data sets. Data from each of these surveys have been previously published (1–3,6–8). A summary of the data sets used and the yr of collection is presented in Table 1, together with a description of the physical activity measures employed in each study. The measures used are comparable for each category with a few minor differences. The Pilot Survey of the Fitness of Australians (PSFA) has a walking measure that does not include walking for transport. The Active Australia (AA) survey asked the moderate activity question at the end of the survey, after parceling out gardening and chores, which were included in the moderate measures for the other two surveys. In the case of the PSFA and the Active Recreation on Tertiary Education Campuses (ARTEC) surveys, written consent was obtained. For the AA survey all contact was by telephone and all of those who took part gave verbal informed consent, consistent with relevant Australian legislation and guidelines.

T1-14
Table 1:
Summary of Australian data sets and physical activity measures used.

The ARTEC survey was conducted in 1996 as part of an implementation strategy to reduce the prevalence of cardiovascular disease, funded by the Commonwealth Department of Health and Family Services. A cross-sectional self-report survey was completed by 2729 college students (mean age 24 yr) from four campuses (response rate of 58%). The AA survey was conducted in 1997/8 in order to provide a national estimate of physical activity to act as benchmark information for a national campaign (Active Australia) to promote physical activity. It was funded by the Commonwealth Department of Health and Family Services, the Australian Sports Commission, and a range of other state and local agencies. The methods for the survey comprised a computer assisted telephone interview system, using random household sampling that targeted adults aged 18–75 yr (response rate of 81%). Final sample weighted data consisted of 2500 adults. The PSFA survey was conducted in 1991 as the first representative population sample on exercise and fitness levels of Australians, funded by the Commonwealth Department of the Arts, Sport, Environment and Territories. The sample was randomly selected from metropolitan Adelaide, South Australia, using a three-stage sampling procedure (generated by the Australian Bureau of Statistics) of electoral rolls with 2300 adults, aged 20–69 yr participating (response rate 75%).

“Sufficient” activity.

Estimated energy expenditures were derived from the frequency and duration of participation in walking, moderate, and vigorous exercise reported in the previous 2 wk. The rate of energy expenditure for each type of activity, in metabolic equivalents, was multiplied by the total time engaged in the activity over the past 2 wk. These values were then summed to yield a total energy expenditure expressed as kcal·wk-1, which was then used to classify respondents into sufficient (≥800 kcal·wk-1) or insufficient (≤800 kcal·wk-1). Sufficient activity broadly equates to meeting current recommendations of 30 min of moderate-intensity physical activity on most days of the week. It is in accordance with the cutoff point used in previous Australian studies (2–4).

Statistical Analyses.

Separate analyses were conducted to examine patterns of physical activity participation in each of the data sets. Age-related patterns of physical activity participation for walking, moderate-intensity activity, vigorous activity, and participation in sufficient physical activity for long-term health benefits were examined using chi-square tests for Linear Trend (χ2LT;5). Gender differences in age-related patterns of physical activity participation were examined using chi-square tests (χ2) for each physical activity category.

RESULTS

Age-related patterns of physical activity participation.

For vigorous activity, overall participation rates are similar between the data sets. Chi-square tests for linear trend (χ2LT) revealed significant differences with age (ARTEC χ2LT =26.7, df = 1, P < 0.001; AA χ2LT =5.6, df = 1, P = 0.02; PSFA χ2LT =4.7 df = 1, P = 0.03;Fig. 1). Participation rates for moderate-intensity activity showed the same trend with a slightly lower participation rate (not significant) for the AA data—this survey asked a more narrowly-defined question about moderate-intensity activity (ARTEC χ2LT =25.1, df = 1, P < 0.001; AA χ2LT =1.65, df = 1, P = 0.19; PSFA χ2LT =7.4, df = 1, P = 0.006;Fig. 1).

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FIGURE 1:
Prevalence for types of activity according to age group for three data sets: Active Recreation or Tertiary Education Campuses (ARTEC); Active Australia (AA); Pilot Survey of the Fitness of Australians (PSFA).

There were no significant differences in walking participation between age groups (ARTEC χ2LT =0.93, df = 1, P = 0.33; AA χ2LT =1.1, df = 1, P = 0.29; PSFA χ2LT =1.9, df = 1, P = 0.15;Fig. 1). PSFA data showed lower participation rates (this survey did not include walking for transport). There was a difference in the percentage of those who are sufficiently active across age groups, which was not significant for AA data (ARTEC χ2LT =12.13, df = 1, P = 0.001; AA χ2LT =1.85, df = 1, P = 0.17; PSFA χ2LT =8.6, df = 1, P = 0.003;Fig. 1).

Gender differences in age-related patterns of physical activity participation.

Comparison of prevalence rates separately for males and females highlighted a number of differences. Males consistently reported higher rates of participation within each of the age groups in vigorous- and moderate-intensity activity, and consequently had higher rates of sufficient activity than did females. Females however, reported higher rates of participation within each of the age groups for walking than did males. Although both males and females consistently showed a difference between age groups for vigorous- and moderate-intensity activity, the decrease is greater for males over the entire age range. Furthermore, despite doing less physical activity overall than males, significant differences in sufficient activity were not observed for females through young adulthood (Table 2).

T2-14
Table 2:
Proportions participating in vigorous- and moderate-intensity activity, walking, and sufficient activity for males (M) and females (F) by age category.

Males consistently showed a significant difference (P < 0.05) between age groups for vigorous-intensity activity. The same pattern of difference was also observed in females but is only statistically significant in the ARTEC data. There was a significant difference (P < 0.05) between age groups for moderate-intensity activity in males in two of the surveys and a statistically nonsignificant trend in the third (AA). Females show the same pattern of difference but the difference was only significant in the ARTEC data. There were no significant changes in the walking participation rates for either males or females. Males but not females showed significant differences (P < 0.05) for sufficient activity in two of the surveys and the same trend in the third (AA). There were no differences observed for walking among males or females.

DISCUSSION

Young adulthood represents a potential preventive window in which lifelong physical activity habits and behaviors may be positively influenced. We found significant differences in the proportions of young adults in successive age groups participating in vigorous and moderate-intensity activity and being sufficiently active for long-term health benefits. Public health action may require more specific interventions in early adulthood to influence relevant determinants in order to promote adoption and maintenance of moderate-intensity physical activity. However, studies of the determinants of physical activity have mainly used vigorous exercise or a measure of total physical activity as outcomes; the determinants of moderate-intensity activity and walking are less well-understood (11).

The study is limited to inferences drawn from secondary analyses of Australian population data surveys. The three surveys used similar measures but in different modes: self report, telephone, and interview administered. Nonetheless, the similarities across these data sets strengthen the evidence that the observed differences among young adult populations are likely to be real.

It may be that the patterns of difference observed in our data are in part due to the changing lifestyle patterns that accompany the transition in personal circumstances and the competing time demands of work or tertiary study. The accompanying changes that occur to proximal physical environments at this life stage may not be supportive of being active. Physical activity campaigns have tended to target middle-aged and older adults (9). However, it may be pertinent to address the decrease in activity earlier in adult life, before physical inactivity becomes habitual and when young adults establish what in many cases may be life-long habitual sedentariness.

The differing patterns of physical activity decreases for males and females have implications for the implementation of population-based physical activity promotion campaigns. Strategies that take into account gender differences in physical activity may be more likely to be efficacious than are those that fail to account for these differences. For example, males are more likely to engage in vigorous physical activity, whereas females are much more likely to engage in walking. However, the steep decreases in vigorous activity reported here and elsewhere (10) for males may indicate that, when males stop doing vigorous sporting and fitness activities, they may be unlikely to replace these with more-moderate forms of activity such as walking or cycling. At the same time, females are reporting doing more walking than are males, and despite having lower levels of activity overall are more likely to maintain sufficient levels of physical activity as their age increases in early adulthood.

Campaigns and environmental strategies that either reinforce these patterns or facilitate complementary activities could be helpful. Specifically, these could encourage males to adopt forms of moderate physical activity and females to adopt other forms of moderate activity to complement walking. These findings indicate potential opportunities for public-health strategies intended to promote the maintenance of physical activity into adulthood and help reverse the decrease in physical activity that occurs before middle age.

The Active Recreation on Tertiary Education Campuses (ARTEC) survey was funded by the Commonwealth Department of Health and Family Services. The Pilot Survey of the Fitness of Australians (PSFA) was funded by the Department of Arts, Sport, Environment and Territories. The Active Australia (AA) Victorian Surveys were funded by the Commonwealth Department of Health and Family Services, Australian Sports Commission, and a range of state agencies.

Address for correspondence: Eva Leslie, MHN, Faculty of Health and Behavioural Sciences, University of Wollongong NSW 2522, Australia; E-mail: [email protected]

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Keywords:

WALKING,; MODERATE-INTENSITY ACTIVITY,; VIGOROUS-INTENSITY ACTIVITY,; PREVALENCE

© 2001 Lippincott Williams & Wilkins, Inc.