Physical activity assessment - case scenarios

Physical activity intervention among preschoolers

Researchers plan to implement and evaluate the potential efficacy of a 12-week pilot program to promote physical activity in a pre-school setting (3–5-years old). They have recruited two pre-schools and plan to randomise them to either intervention or control group. Physical activity will be assessed among approximately 50 children (25 in each group) at baseline and 6 months. The researchers would like to determine if the intervention program results in greater participation in physical activity during the pre-school day and if a greater proportion of students are active during structured physical activity sessions.

In this scenario, the researchers are assessing changes in physical activity within a relatively small group of participants over time using a cluster-randomised trial. Key outcome variables of the evaluation are the duration and intensity of physical activity participation during the pre-school day and the proportion of children who are “active” during structured physical activity sessions. The number of days that should be assessed to capture habitual activity patterns in this age group and in this setting is unknown, and will depend on day-to-day variations in the pre-school program.

Given that the participants are too young to self-report, two approaches might be used in tandem: direct observation and accelerometry. Direct observation can be used to assess the number of children who are active in a particular area (in this case, an indoor or outdoor play space) during a specific period of time. As such, it could be used to assess the proportion of children who are active during a structured physical activity session.

A strength of this measure is that it can be used with little burden on the children. As it would be too onerous to use direct observation across the entire pre-school day, accelerometers could be used since the sample size is sufficiently small to bear the relatively high cost of these instruments. As data are captured in ‘real time’, it can also provide information on the activity levels of children during the structured physical activity sessions to obtain a more complete picture of these bouts of physical activity.

Prevalence survey among adolescents

There is concern in the community about decreasing levels of physical activity among adolescents. A sample of >1000 female and male students from different year levels and a variety of schools, educational sectors and geographic locations will be recruited. Physical activity will be assessed at one point in time (point prevalence design). Conducting a needs assessment prior to the development of physical activity promotion programs is essential for identifying appropriate behavioural targets that meet the most important needs of the community and are likely to make the greatest impact.

In this scenario, it would be important to establish the proportion of the population that meets young people’s physical activity guidelines and to provide a benchmark against which the effectiveness of physical activity programs in the community can be compared. It would also be important to determine the types or domains of physical activities among young people to establish target behaviours (e.g., active trans-port, organised sport, school-based physical activity).

The adolescent age group (12–18-years old) is of interest in this study and therefore self-report is an option. Given the need to describe physical activity quite broadly, and the likelihood of requiring a relatively large sample size, simultaneous cost-effective subjective and objective methods would be favored: self-report (most likely self-administered in this large sample) and if the budget allows, pedometers.

Self-report physical activity recall instruments can assess compliance with guidelines and the types or domains of physical activity in which the respondents engage. Pedometers measure ‘steps’ and therefore can be used to establish a benchmark for how much walking is performed. While the pedometer is unable to represent other dimensions of physical activity (i.e., intensity or contextual information about where walking took place) the objective information on walking complements the self-report since incidental walking is particularly difficult to recall and therefore poorly captured by self-report.

Treatment program for overweight and obese adolescents

A researcher has received funding to test the feasibility and acceptability of a 26-week obesity treatment program among overweight and obese adolescents (aged 13–18 years) in a community setting. He/she plans to recruit 12 participants to the feasibility trial (as a single group) and assess their physical activity at pre- and post-intervention. The researcher would like to determine the potential efficacy of the program on the amount of time spent in MVPA outside of school hours.

In this scenario, the researcher is interested in examining changes in habitual physical activity over time. It is important to capture, as accurately as possible, the amount of time spent in specified intensities of physical activity (moderate and vigorous). While the sample size is relatively small, direct observation is not feasible since the time period of interest is outside of school hours. The errors associated with self-report (and factors such as social desirability bias) are likely to limit the ability to detect changed behaviour with sufficient resolution.

Therefore, an objective measure is recommended, and accelerometry provides the advantage of real-time data acquisition over pedometers. This allows periods outside of school hours to be partitioned from other time periods. Researchers can use cut-points developed for this age group to provide information about the intensity of the physical activity.

Trial of a school-based obesity prevention program

A research team has developed a 20-week school-based obesity prevention program that they would like to implement and evaluate with 6–9-year-old children. They have recruited 10 schools to the study and plan to randomize them to intervention (n = 300 children) or control (n = children) groups and assess children’s physical activity pre and post-intervention. They would like to determine if there has been an increase in school-based physical activity during physical education, recess, and lunch, and in the duration of different types of physical activity out of school hours and on weekends.

In this scenario, the researchers are interested in changes in physical activity over a 20-week period. The relatively large sample comprises children who are too young to self-report, and the study requires details of levels and types of physical activity. This limits the choices to cost-effective objective methods and proxy-reported subjective methods.

For activities performed at school, teacher proxy-reports would be preferred, although teachers’ assessments are likely to be more valid for structured classroom activity than free play at recess and lunch. For free play at recess and lunch, direct observation of participation in a physical activity setting (such as an oval or quadrangle) could be undertaken by trained assessors. For an overall assessment of school-based physical activity, pedometers could be worn from the beginning to the end of the school day, with readings taken at the beginning and end of recess and lunch breaks to isolate these periods.

It would be recommended that multiple assessment days be used to minimise the inflation in the intra-class correlation coefficient arising from assessments being conducted in a school on the same day. A parent proxy-report could be used to assess physical activity types and durations out of school hours.

A clinical application

A clinician is interested in determining the physical activity status of a 14-year-old child with Type-2 Diabetes prior to advising or prescribing physical activity / exercise. A number of potential approaches could be applied in this clinical setting, including: self-report questionnaire or diary/log; pedometer; HR monitor; or a combination of methods. In this example, the importance of using a multi-method approach should not be underestimated.

A rudimentary assessment of physical activity level (including the young person’s preferences for physical activities), may be performed using a standardised self-report questionnaire screening survey or diary, and a pedometer as a component of initial health screening. A pedometer may be used as a screening tool and as a source of motivation (self-monitoring) for the child to adopt a more physically active lifestyle.

A major advantage of establishing an objective measure of an individual’s baseline activity is the ability to provide a quantifiable and tailored dose of physical activity or exercise prescription. The starting point in the use of a pedometer should be to determine the number of steps an individual takes to cover a defined distance (for example, 1 km) and then a baseline number of steps over a minimum of 1 week (including weekend and weekdays). Consequently, the clinician is able to recommend a realistic number of ‘steps per day’, working towards the recommended number of steps for young people or if this is already met, a realistic number beyond.

For further information see:
Dollman J, Okely AD, Hardy L, Timperio A, Salmon Jo, Hills AP. A hitchhiker's guide to assessing young people's physical activity: Deciding what method to use. Journal of Science and Medicine in Sport 2009; 12(5):518-525. Abstract