Absolute Accelerometer-Based Intensity Prescription Compared to Physiological Variables in Pregnant and Nonpregnant Women

Estimation of the intensity of physical activity (PA) based on absolute accelerometer cut points (Cp) likely over- or underestimates intensity for a specific individual. The purpose of this study was to investigate the relationship between absolute moderate intensity Cp and the first ventilatory threshold (VT(1)). A group of 24 pregnant and 15 nonpregnant women who performed a submaximal incremental walking test with measures of ventilatory parameters and accelerations from three different accelerometers on the wrist (ActiGraph wGT3X-BT, GENEActiv, Axivity AX3) and one on the hip (Actigraph wGT3X-BT) were analyzed. Cp were determined corresponding to 3 metabolic equivalents of task (MET), using the conventional MET definition (Cp(3.5)) (3.5 mL/kg×min) and individual resting metabolic rate (Cp(ind)). The ventilatory equivalent (VE/VO(2)) was used to determine VT(1). Accelerations at VT(1) were significantly higher (p < 0.01) compared to Cp(3.5) and Cp(ind) in both groups. Cp(3.5) and Cp(ind) were significantly different in nonpregnant (p < 0.01) but not in pregnant women. Walking speed at VT(1) (5.7 ± 0.5/6.2 ± 0.8 km/h) was significantly lower (p < 0.01) in pregnant compared to nonpregnant women and correspondent to 3.8 ± 0.7/4.9 ± 1.4 conventional METs. Intensity at absolute Cp was lower compared to the intensity at VT(1) independent of the device or placement in pregnant and nonpregnant women. Therefore, we recommend individually tailored cut points such as the VT(1) to better assess the effect of the intensity of PA.