Indication
Accelerometers were initially used as an outcome measure in small studies and a criterion measure to compare self-report data. As accelerometers have advanced and become cheaper they have increasingly been used in large studies, including thousands of participants in for example the European Youth Heart Study (Riddoch et al, 2005), the UK Avon Longitudinal Study of Parents and Children (ALSPAC) (Golding et al, 2001) and the NHANES (Troiano et al, 2008). An overview of accelerometry processing and compliance patterns in the ALSPAC study has been described (Mattocks et al, 2008). Nowadays, accelerometry is even used in sub-samples of national diet surveys in both the UK and US, e.g the National Health and Nutrition Examination Survey in the US and the Health Survey for England. The collection of physical activity data in real time is an important advantage over self-report methods in large surveys. It should be noted that evidence from accelerometry studies have identified relationships between physical activity, sedentary behaviour, obesity and cardiovascular risk factors (Andersen et al, 2006; Balkau et al, 2008; Ekelund et al, 2007; Ness et al, 2007); these associations are partly attributable to the more accurate and precise measure of physical activity (Reilly et al 2008).
Accelerometers are therefore suitable for large-scale observational cohort studies, and studies undertaking association analyses between exposure(s) and outcome (s). They can also be used in interventions and randomised controlled trials to examine intervention or treatment efficacy.
There are, however, limitations with accelerometry and improvements to make the method more feasible and provide a more detailed, accurate picture of physical activity are required.