Among the techniques to assess the amount and patterns of physical activity, accelerometry has received particular attention due to ease of use, reliability, and objectivity of the results. These factors combined with technological advances in the last decade led to substantial increase in accelerometers use for the PA measurement in various populations including youth Accelerometers are movement monitors that have the ability to capture intensity of physical activity. They are attached typically to a person waist with a belt clip; however, some monitors can also be work on the wrist or ankle
Accelerometers operate by measuring acceleration along a given axis, using any of a number of technologies including piezo–electric, micro–mechanical springs, and changes in capacitance. Multiple sensors can also be bundled into a single monitor, allowing movement to in multiple planes of movement to be captured. The major function of accelerometers is that the sensor converts movements into electrical signals (counts) that are proportional to the muscular force producing motion. These counts are summed over a specified time period (epoch) and stored. The counts recorded by accelerometers can be compared to laboratory-established cut points to relate to metabolic equivalents (MET) values.
Accelerometers have been utilized in a variety of research settings and proven a reliable and valid assessment of physical activity in various populations ranging from children to older adults. However, it is important to note that each population has its own challenges and can require a range 3–12 days of monitoring for accurate assessment.
Accelerometer equations have been developed for specific activities (e.g. walking, running, rest) and do not accurately estimate other activities (e.g. stationary biking, elliptical trainer). The consensus is that for activities entirely composed of flat-ground ambulation and rest, accelerometers can provide objective measures of activity. Accelerometers also do not capture upper extremity movement causing underestimation of activities such as typing, playing computer games, washing dishes or performing specific exercises including weight-bearing activities.