Accelerometer

Accelerometers measure body movement in terms of acceleration.
- Placement
  - Belt or waistband
  - Wrist-worn (less obstruction)
- Outcomes
  - Counts
    - Product of amplitude and frequency of the acceleration
  - Energy expenditure
    - Linear regression equation: counts + personal info
  - Intensity classification
    - Intensity cut offs for activity counts
  - Steps
- Mechanisms
  - Registration of acceleration on 1, 2 or 3 axes
  - Piezo-electric sensors
    - Voltage proportional to acceleration
    - Filtering of raw signal
Research devices
Consumer devices
Pros
- Accurate
- Information on patterns of PA: minute by minute data
  - Duration, intensity, frequency
- Multiple days of monitoring possible
- Access to raw data
Cons
- Missed activities
  - Upper body, load carrying, cycling, water based
- Requires technical expertise (research)
- Different intensity cut-offs (generalisation)
- Underestimation at highest intensities