Accurate quantification of physical activity energy expenditure is a key part of the effort to understand disorders of energy metabolism. The Actiheart, a combined heart rate (HR) and movement sensor, is designed to assess physical activity in populations.

Objective:

To examine aspects of Actiheart reliability and validity in mechanical settings and during walking and running.

Methods:

In eight Actiheart units, technical reliability (coefficients of variation, CV) and validity for movement were assessed with sinusoid accelerations (0.1–20 m/s 2) and for HR by simulated R-wave impulses (25–250 bpm). Agreement between Actiheart and ECG was determined during rest and treadmill locomotion (3.2–12.1 km/h). Walking and running intensity (in J/min/kg) was assessed with indirect calorimetry in 11 men and nine women (26–50 y, 20–29 kg/m 2) and modelled from movement, HR, and movement+ HR by multiple linear regression, adjusting for sex.

Results:

Median intrainstrument CV was 0.5 and 0.03% for movement and HR, respectively. Corresponding interinstrument CV values were 5.7 and 0.03% with some evidence of heteroscedasticity for movement. The linear relationship between movement and acceleration was strong (R 2= 0.99, P< 0.001). Simulated R-waves were detected within 1 bpm from 30 to 250 bpm. The 95% limits of agreement between Actiheart and ECG were− 4.2 to 4.3 bpm. Correlations with intensity were generally high (R 2> 0.84, P< 0.001) but significantly highest when combining HR and movement (SEE< 1 MET).

Conclusions:

The Actiheart is technically reliable and valid. Walking and running intensity may be estimated accurately but further studies are needed to assess validity in other activities and during free-living.