Evaluating Physical Activity

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How to Measure / Quantify Physical Activity

There are many reasons that, as physiotherapists we might want to measure PA levels.  Before you think about how to measure, think about why you want to measure and who the information is for.  For example you might want to measure for any of the following reasons;

1. To understand baseline levels in the population of interest?
2. To see whether a certain intervention is having an impact on PA levels?
3. To motivate patients by showing progress?

Each of the above reasons might require a different type of data, for a different audience with a different objective.

There are also different components of PA that can be measured, for example you could measure the frequency with which some one is physically active, the intensity of their activity, the type of activity they engage in and the duration of that activity.  In some situations it's more appropriate to measure one of these aspects of activity but frequently it's more practical to try to get an overall meaurement of someones activity (their total physical activity over a given period of time).  It's really important to keep in mind that none of these measures are perfect and they all have advantages and disadvantages, it's a case of weighting up the pros and cons of a selection of measures in a given context.

Ways of Gathering PA data

Exisiting Records

This might include using information that is routinely collected, for example census information, surveys, polls, government data.  There is more information available than ever before, think back to week one, you were asked to identify local sources of PA data.  Sometimes the existing data doesn't quite meet our needs, this could be for many reasons including; it may be too broad and not focus on our population of interest, it may be in a format that doesn't suit us, it may have been gathered in a way that we don't feel is sufficiently detailed or it may be out of date.

Indirect Measures

These rely on self-report i.e. they ask the patient to estimate how much activity they have done in a given period.  They are useful because they are cheap and easy to complete.  There are obvious issues with relying on recall though, they may not be appropriate for some older populations and people with dementia for example.  There are also other issues such as trying to give a favourable result to please the assessor.  

There are lots of questionnaires and surveys available, in 2011 the UK National Obesity Obervatory produced a report which reviewed the available tools and suggested the following shortlist are the most robust measurement tools (this doesn't mean that they are user friendly though!).   

Shortlist of selected questionnaires Physical activity: children and young people

1. The Physical Activity Questionnaire for Older Children/Adolescents (PAQC/PAQ-A)
2. Youth Risk Behaviour Surveillance Survey (YRBSS)
3. The Teen Health Survey

Physical activity: adults

1. Stanford 7-day recall (7-DR)
2. International Physical Activity Questionnaire Long version (IPAQ-Long)
3. New Zealand Physical Activity Questionnaire (Short Form) (NZPAQ-Short)
4. 7-day Physical Activity Diary
   

The IPAQ is a very well known method of quantifying physical activity levels, it's a useful document to find out more about quantifying and measuring physical activity:

• International Physical Activity Questionnaire (IPAQ) 
  

Direct Measures

Direct measures use technology to measure activity levels, this is usually in the form of a device that will measure and record movement.  This might be a simple pedometer, an app on a smart phone or a sophisticated movement tracker.  

Direct measures are considered to be more accurate than self-report measures but they are costly and may not be appealing to some patients.  They also have limitations including;

• Variable ability to detect very slow walking speeds; obvious implications for clinical populations.
• Variable ability to measure movement in abnormal gait patterns.
• Variable ability to gather data on certain types of activity.  Walking is usually fine but if the monitor is worn on the lower limb, upper limb activity is unlikely to be detected.  This has implications for wheelchair users or anyone who engages in chair-based exercise.

Literature suggests that there is little agreement between indirect and direct measures.  However because of the barriers to accessing technology indirect measures are still frequently used.  This article by Skender et al 2016 explores correlations between self-reported PA and accelerometer data.</span>

Kowalski 2012 performed a systematic review of studies that had used direct and indirect tools to measure PA in older adults. Sylvia et al 2014 give a comprehensive  but very readable overview of different measures.  This article by Sallis 2011 gives an example of direct and indirect measures are used in evaluating a PA programme for a specific population. 

Challenges
The more robust and reliable these are the more detailed and time consuming they become. Trying to find something that it valid, reliable AND user-friendly in clinical practice is a really difficult!  It's important to remember;

• Health and PA behaviours are complex.
• Changes may take a long time to become apparent.
• Different stakeholders are interested in different things.
• You simply can't measure everything.

To finish this section have a look at this short clip on Youtube on PA measurement; https://www.youtube.com/watch?v=kKHjnAzK86o and then review this webpage from Medical Research Council. http://dapa-toolkit.mrc.ac.uk/physical-activity-assessment/methods/index.php</span>

References

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