Accelerometry has been proposed as an objective method for measurement of physical activity. Detailed information on the technical performance of these devices is lacking.

PURPOSE

To study the intra- and inter-instrument reliability and validity of the Computer Science & Applications (CSA) Model 7164 accelerometer, along with the nature of the analogue filter in the device with sinusoidal movements in a mechanical setting.

METHODS

Six CSA units were tested with 17 different frequencies (0.5–4Hz) on three radius settings (0.022–0.049m), yielding 51 different acceleration settings (0.1–19.7 m·s⁻²).

RESULTS

Intra-instrument reliability was relatively good (mean CV of 4.4%), although questionable on extreme values of acceleration (< 1 m·s⁻² and > 16m·s⁻²). Analyses on inter-instrument reliability revealed both overall systematic bias and acceleration-specific differences between units, approaching unit error magnitudes of 20% from the mean of all 6 units. The correlation between CSA output and acceleration (i.e., validity) was significant but the relationship was clearly nonlinear. Applying equations to cancel the frequency-dependent filtering restored this linearity (r² = 0.97).

CONCLUSION

The CSA exhibits reasonable intra-instrument reliability but large unit differences call for unit-specific calibration or alternatively statistical adjustment. Linearity between CSA output and acceleration is achieved only by correcting for movement frequency filtering.