The paper reviewed here is ‘Distinguishing Four Components Underlying Physical Activity: A New Approach to Using Physical Activity Questionnaire Data in Old Age’ by Verweij and colleagues published in BMC Geriatrics and freely available here. Exercise is an activity that has important health benefits across the spectrum although the relationship is undoubtedly complex. The possibility of reducing the prevalence of illnesses or reducing morbidity means that this is an important area of investigation. In terms of the complexity of the relationship between exercise and health, the researchers in this study investigate how physical activity can be deconstructed allowing an examination of exercise components from self-reported data.
Aims: The researchers clearly state their aim thus:-
‘The aim of this methodological study was to propose a method for distinguishing four components underlying self-reported physical activity of older adults: intensity, muscle strength, turning actions and mechanical strain‘
Method: The researchers sampled 1699 older adults from another study – the Longitudinal Aging Study Amsterdam. In this study, 3107 people aged between 55 and 85 years were recruited from ‘three areas in the Netherlands and were stratified for age, gender and 5-year mortality at baseline‘. The researchers excluded people experiencing difficulties with mobility and this population would benefit from more specialised research in this area. The researchers used the answers to the LASA Physical Activity Questionnaire (LPAQ). However a copy of the questionnaire was not included in the paper. Although frequencies of responses to items on the questionnaire are given, inclusion of the original questionnaire would better guide a fuller understanding of the results. Several components were chosen – intensity, muscle strength, mechanical strain and turning actions. An objective measure of muscle strength was used but for the other measures expert consensus provided estimates for the component scores on each activity (I thought there might be the possibility of undertaking future quantitative research to supplement the consensus scores). In order to examine construct validity, the researchers compared the measured strength scores with the component scores. They also undertook a principal components analysis using the four constructs with the self-reported data.
The average age in the sample was 73 years.
Three components were identified
‘1. Intensity and muscle strength loaded on the same factor
2. Mechanical strain and
3. Turning actions‘
The correlation of muscle strength and measured muscle strength provided evidence of construct validity. The principal component analysis provided evidence of three distinct categories as noted above with intensity and muscle strength grouped together as a single component.
Conclusions: The researchers conclude with a comprehensive discussion outlining how these results might be used to inform guidance as well as to investigate the relationship between specific illnesses and exercise. I thought that this was an elegant paper with simply stated methodology, robust statistical analysis and long term clinical applications via further research together with a detailed discussion of the results. It would be interesting to see what results this type of analysis might produce when applied to illnesses such as psychosis, depression and dementia.
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