Every step counts
Promoting physical activity in obese adolescents
by Stuart Trost
(Dr Trost, NH&MRC Research Fellow in Physical Activity and Health at the University of Queensland, has been researching activity levels in children and adolescents.)

The prevalence of obesity among Australian children has risen dramatically in recent decades.

Though dietary changes may have contributed to this alarming trend, available evidence indicates that decreased physical activity is a major contributing factor. This observation indicates that public health efforts to attack the burgeoning obesity rate in children should focus on promotion of physical activity. Unfortunately, the scientific literature provides relatively little guidance concerning effective interventions to promote physical activity in children.

It is widely believed that physical activity levels among children have declined because of changes in the social and physical environment in which they grow up. These changes include increases in television watching, use of the Internet and playing video games. Other potentially important factors are parental modelling of physical activity, dependence on motorised transport, and families in which both parents work outside the home.

It is hypothesised that the net effect of these societal changes has been to reduce the exposure of children to social and physical environments that encourage physical activity and increase their exposure to environments that deter, limit or discourage it.

My colleagues and I at the University of Queensland are currently conducting a study to promote regular physical activity in overweight and obese adolescents. The specific aims are to:
• explore the acceptability of, and compliance with, a 10-week home-based moderate-intensity physical activity program for obese adolescents, and
• evaluate the effects of the program on insulin sensitivity and other components of the insulin resistance syndrome, including fibrinolytic activity, plasma triglycerides, and resting blood pressure in obese adolescents.

Following preliminary screening and baseline assessments of the insulin sensitivity and other risk factors, participants completed a 10-week home-based physical activity program consisting of moderate intensity aerobic activities such as walking five days a week and increased “lifestyle” related activity every day.

Those taking part and their family members were given an electronic pedometer (Yamax Digiwalker SW 700) to monitor the number of steps taken daily.

After establishing a baseline level of activity, participants signed a behavioural contract specifying a “steps per day” goal for the next 2 weeks, the activities (planned and incidental) that would be performed to reach the goal, and the reward for reaching the goal. Participants were also given a personalised diary to record the time of day the monitor was worn each day, daily pedometer steps and duration of any activities not recorded by the pedometer (ie, swimming or cycling).

They were visited by a research assistant every two weeks, to set a new goal and to discuss any problems associated with meeting the set pedometer goal. Emphasis was placed on moderate-intensity physical activities such as walking.

To date, 17 participants have completed the program. The figure shows the mean change (relative to baseline) in daily pedometer steps over the 10-week period. Though the results are preliminary, they support the efficacy of pedometers in promoting regular physical activity in obese adolescents.

Our next step is to examine whether these changes in physical activity result in changes in insulin sensitivity and other components of the insulin resistance syndrome.