There are several areas of weakness within the existing literature on physical activity in older people. The first concerns the robosity of studies conducted, particularly the design and sampling aspects of the methodology. Robosity is a challenge for all studies, not just those involving older people. Secondly, there are relatively few reviews that focus specifically on older people, raising concerns about the generalisability of studies of the overall adult population. Thirdly, there has been relatively limited use of data collection instruments specifically designed for use with older people. These influences upon the interpretation of data from the evidence base were noted throughout the production of this discussion document and are briefly discussed below.
Common methodological limitationsMethodological weaknesses highlighted in the general physical activity literature also pertain to studies involving older people. The limitations include: small samples, lack of detail regarding the intervention, variable means of recording physical activity behaviour, absence of intention to treat analyses and limited follow-up periods. All impact on the validity and generalisability of the findings and make cross-study comparison difficult.
Whilst a statistical or clinical benefit may be reported, there is often little reference to whether national guideline criteria have been met, i.e. whether the physical activity behaviour level is sufficient to produce health benefits overall. Indeed, several studies with older people may have reported statistically significant differences between intervention and control groups, but the additional amount of physical activity achieved may be relatively modest.
There is also limited evidence for the sustainability of physical activity behaviour change and associated health outcomes over time. Recent reviews of physical activity programs for older people have reported that the impact is often short term and relatively small (van der Bij, Laurent et al. 2002). Notable exceptions are the CHAMPS study, which had a one year follow-up (Stewart, Mills et al. 2001) and Campbell et al’s home based falls prevention exercise program that had a two year follow-up period (Campbell, Robertson et al. 1999).
Internal and external validity: generalising to older peopleTwo fundamental methodological issues hamper the evidence for physical activity promotion in older people. Firstly, there are relatively few reviews that focus specifically on older people. For example, the recent Cochrane review (Hillsdon, Foster et al. 2005) included four studies that focused on older people. Seven had samples with a maximum age of sixty or below and the remaining ten contained people 60 or above. Some provided a maximum age, but more often the paper only states 60+, which does not allow for any discrimination across the older adults represented. Where studies have included older people, it is not always possible to determine the intervention’s impact on this sub-group. Only one study (Stewart, Mills et al. 2001) compared outcomes between those above and below 75 years old: no difference in outcomes between the two age groups was reported.
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Secondly, many studies have used instruments meant for the general adult population. Details of physical activity are key in older people. For example, the absolute intensity of activity measured on a scale may not reflect the relative underlying capacity of the person to exercise. To date, only four instruments have been developed for use with older people (Washburn 2000). These are the Physical Activity Scale for the Elderly (PASE) (Washburn, Smith et al. 1993), the Yale Physical Activity Survey (DiPietro, Caspersen et al. 1993), the Zutphen Physical Activity Questionnaire (Caspersen, Bloemberg et al. 1991) and the Modified Baecke Questionnaire for Older Adults (Baecke, Burema et al. 1982). The instruments have been psychometrically tested and are reasonably robust, but further testing is needed. Objective measures, such as calorimetry and doubly-labelled water techniques, are likely to be infeasible in community implementation trials. Self-report measures are impeded by recall and over-reporting bias. Further, the instruments have often been designed for males living in Western cultures, so their appropriateness for not only older people, but women and those from CLDB backgrounds, is unclear (Seefeldt, Malina et al. 2002). Evaluation of the impact of future programs clearly requires accurate measurement of physical activity behaviour, using measures appropriate for a multicultural older population.
A recent systematic review (Jorstad-Stein, Hauer et al. 2005) found that none of the currently available tools is wholly suitable for future trial usage. They recommended that new tools be developed, or the more robust ones, such as the Stanford 7-day Physical Activity Recall and the Community Health Activities Model Program for Seniors Questionnaires, be further developed.
Thirdly, the heterogeneous nature of the older population makes measurement challenging even when age relevant tools are used. This is because disability and impairments associated with chronic disease can influence the conduct of physical activity and the reporting of its duration and intensity. For example, it can take longer for a mobility impaired person to walk a set distance and it can involve more effort. This means that their reporting of such activity can be skewed to make it appear to be longer and of greater intensity than in a healthy person. Thus it is preferable to focus on the frequency of physical activity rather than duration or intensity. Alternatively, data could be adjusted according to the person’s functional status.
In summary, measurement limitations impact on our ability to assess the effectiveness of physical activity interventions and different people’s responses thereto. Measurement tools have given us some understanding of physical activity patterns and barriers to physical activity. There is an ongoing need for methodologies that allow researchers to capture why people do maintain physical activity behaviours, so that this information can be used in motivating others.
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