Physical activity assessment – Diary or log
Self-reports of physical activity by a diary or log method provide a detailed record of an individual’s physical activity on a daily basis; these records are generally completed prospectively as the activities are completed. In a physical activity diary (also known as a record), individuals are instructed to record the individual bouts of activity as they occur during the day. In contrast, logs capture the time individuals spend in broad categories of activity: inactive, sitting, light, moderate, vigorous and very vigorous and examples of activities in each intensity level are provided (Bouchard et al, 1983).
In both the diary and log, the 24 hour period is typically broken down into 15 minute segments and individuals record their activity. Completing diaries and logs every 15 minutes may lead to the omission of some activities, but reducing the period has been shown to be too intensive and lead to non completion (Bratteby et al, 1997).
In diaries, individuals are asked to record their activity often from a pre-defined list which is coded, but space is provided for other activities to be recorded. The list of activities is typically grouped according to their metabolic equivalents (MET) value. The intensity of the activity (low, moderate or vigorous) is also recorded.
Ainsworth et al (2000a) have developed and tested a logbook which is a page long per day and contains 48 items (7 resting/light; 25 moderate; 16 hard/very hard) organised as home, transport, occupation, conditioning, sports and leisure activities (intensity was not sought in the later version). Individuals are instructed to complete the log book at the end of each day and record only activity with duration of more than 10 minutes. This log book is less burdensome than others. Correlations with accelerometry were moderate and ranged from 0.26-0.54 depending on the comparisons.
Diaries produce more detailed information i.e. types of activity, intensity and patterns, than logs but are more burdensome for individuals to complete and the data are more complex to reduce and enter. The recent development of palm-top personal digital assistants has enabled this electronic medium to be utilised for the collection of physical activity data by a diary method (Mathews, 2002).
The compendium of physical activities first published by Ainsworth et al (1993) was crucial to a uniformed approach to analysing self-reports, particularly from diaries and logs, to estimate energy expenditure from physical activity. This compendium was updated in 2000 (Ainsworth et al, 2000b) and a compendium for children has recently been published (Ridley et al, 2008). Both compendia provide energy cost over a wide range of categories of activities and provide examples of activities within each category. An electronic version of the revised adult compendium is available. It should be remembered that the compendia represent average values of the energy costs of an activity over the population and cannot be used in a precise manner at an individual level. The frequency and duration are combined with the MET intensity value to calculate relative energy expenditure and generally reported as MET hours for the time period (e.g. 7 days). One study has investigated the use of the adult compendium in practice, by assessing agreement between raters in assigning MET codes and values, and also raters’ objectivity (Masse et al, 2002). The study had strict training protocols for training raters and the diary described was detailed and generally good agreement was seen, ranging from 44-92%; high objectivity was also noted.
Bouchard’s activity diary has been used in adults and older children and adolescents; associations with physiological measures have been demonstrated (Bouchard 1983). Bratteby et al (1997) compared total energy expenditure estimated from a diary and measured by doubly labelled water in 15 year olds. There was a small mean difference of 1.2% indicating the validity of the diary to estimate energy expenditure at a group level. Another study also demonstrated the validity of an activity diary to estimate energy expenditure at a group level and to record bouts of moderately vigorous activity (Ekelund et al, 1999). Using diaries in young children via proxy reports has been shown to have low reliability (Freedson and Evenson, 1991). In a recent review of the measurement of physical activity in pre-schoolers, only one of the eight studies found for self-report measures used a diary (Oliver et al, 2007). In this study, accelerometer determined activity was compared to results of an activity diary completed every 30 minutes for nine children aged 4-17 months. A moderate association (r=0.42) and low-to-moderate concordance (57-78%) was found between methods (Tulve, et al, 2007).
Accelerometry was compared to a physical activity log in 59 women over 7 days and overall moderate associations were found, ranging from 0.45 to 0.86 depending on the cut-off chosen for the accelerometry data (Schmidt et al, 2003). High test retest reliability (r=0.94) has been reported using the Child/Adolescent Activity Log (CAAT) (Garcia et al, 1998).
There is a concern that keeping a diary or log book of activity will cause individuals to change (increase) their physical activity i.e. a reactivity effect. A study described the determinants (age, body mass index, body fat percentage, physical activity level) associated with over and under reporting activity using a physical activity diary (record), a recall questionnaire, and doubly labelled water (Irwin et al, 2001). Estimation of energy expenditure was found to more accurate with the activity record compared to the seven day recall; higher age and increased percentage body fat was associated with greater over-estimation of activity (Irwin et al, 2001) One study has uniquely examined if keeping physical activity logs influence estimates of validity of 7-day recall physical activity questionnaires and no influence was found (Timperio et al, 2004). In another study it appeared logs were kept more accurately in leaner women compared to those who were overweight (Schmidt et al, 2003).