Resources required
The following resources are usually required in addition to trained personnel:
- Combined sensors
- Interface (e.g. USB)
- Software (for intialisation/download/analysis)
- Charger
As for heart rate monitoring, resources will be required for individual calibration and this will vary according to the degree of calibration. A step test, feasible for field-based research, has been shown to be a suitable means for individual calibration.
Data handling
Branched equation modelling was examined in a study that used the combination of heart rate monitoring and accelerometry against whole-body calorimetry as the criterion standard (Brage et al, 2004). In this analysis method physical activity energy expenditure is estimated with four different weightings for the accelerometer data and heart rate data depending on the intensity of the activity (Brage et al, 2004). That is, in low levels of activities the accelerometry data is relied upon mainly, and at very high intensities heart rate data, with two interim weightings in between. Increasing the range i.e. mode and intensities of activities undertaken in such studies will increase the quantification of the accuracy of the equations used to estimate physical activity energy expenditure, but this study indicated that individual calibration may not be necessary (Brage et al, 2004).
Alternative modelling techniques have been investigated (Strath et al, 2001; Johannsson et al, 2006; Zakeri et al, 2008). Estimates of physical activity energy expenditure from an accelerometer worn at the hip, heart rate alone, and the combined information from heart rate and two accelerometers on wrist and thigh were compared during 14 simulated activities of daily living (Strath et al, 2001). For the combined model, the wrist and thigh motion sensors were used to discriminate which heart rate energy expenditure regression to use and this resulted in greater precision of the physical activity energy expenditure estimation.
The authors of two of these approaches (wrist-thigh motion with heart rate, trunk motion with heart rate) compared modelling techniques, and the influence of two different levels of individual heart rate calibration in a field-based study in 10 men and women using indirect calorimetry as the criterion validation method. Combined sensing, irrespective of modelling technique was shown to accurately reflect physical activity energy expenditure estimation at both a group and individual level (Strath et al, 2005).
Basic analysis software is provided with the Actiheart device. However, new researchers are advised to collaborate with experienced researchers in the field given the complexity of the data.