Why Do Physical Activity Programs Work?

Intervention programs to increase physical activity among children have had either no effects, small effects or small effects in some, but not all, groups of the participating children. Dr. Tom Baranowski, Professor of Pediatrics at the USDA/ARS Children’s Nutrition Research Center and his colleagues are attempting to understand why.

In simple terms, Dr. Baranowski has been examing the variables or the path-ways that come between physical activity interventions and physical activity outcomes. He has proposed the “mediating variable model” to understand why some childhood physical activity interventions succeed and others fail.

A simple framework for the model is shown below.

This model suggests that changes in physical activity behavior are a result of changes in the mediating variables. Examples of some mediating variables include:

• Family support;
• Equipment at home;
• Confidence in finding the time to be active.

“Thus, we design programs to change mediating variables. It’s the changes in mediating variables that lead to behavior change,” states Dr. Baranowski.

There are also moderating vari-ables that may change the outcome of the intervention. For example if a program works for girls but not for boys, gender would be a moderating variable. The outcome of a physical activity intervention could be influenced by using rewards, but the long-term continuation of the intervention and its effects might not be as promising once the intervention and the rewards stop.

In this model, the barriers to suc-cess-ful physical activity interventions are included at every step in the pro-gram implementation. Barriers to success include:

Training - Trainers not well prepared or trainers lack knowledge about learning style of participants

Implementation/Delivery - Trainers do not allow sufficient time, participants have unreal expectations, or trainers focus on words not activities

Use - Inappropriate equipment, in-sufficient time by participants to implement

To be successful, a program should reach a large number of target participants, be culturally sensitive and appropriate for long-term sustained use.

Dr. Baranowski is optimistic that a better understanding of how physical activity intervention programs work will lead to identification of mediating and moderating variables for use in large-scale interventions. More information on this topic as well as the comprehensive model can be found in the October 2005 issue of Exercise and Sport Sciences Reviews.