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

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 (VT₁). 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/VO₂) was used to determine VT₁. Accelerations at VT₁ 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 VT₁ (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 VT₁ independent of the device or placement in pregnant and nonpregnant women. Therefore, we recommend individually tailored cut points such as the VT₁ to better assess the effect of the intensity of PA.