Exercise During Pregnancy: Increased Oxygen Uptake and Metabolic Demand

Current guidelines for exercise during pregnancy are limited in their precision on exercise intensity as the established compendium for exercise modes and intensities is based on estimates in non-gravid adults. To address this gap, we used indirect calorimetry to measure prenatal exercise energy demand during standard aerobic exercises in order to compare intensity to published standards.

Participants (n = 7; 30.7 ± 3.3 yrs of age) completed 5 minutes each of exercise at low and moderate intensity for walking and cycling, on the same testing day, separated < 1 minute. For the first 5-minute bout, the participant performed an external work rate that elicited low intensity exercise, i.e., 40 - 59% peak aerobic capacity (VO₂ peak). This was followed by 5 minutes of the same exercise mode at moderate intensity, i.e., 40 - 59% VO₂ peak. This process was repeated on a cycle ergometer. Measured VO₂ was compared with ACSM-estimated VO₂ at each trimester. Reported results were presented separately for low and high exercise intensities.

Measured absolute and relative VO₂ during walking and cycling exercises were significantly higher (p < .001) in all trimesters compared with predicted values, which corresponded with a 35% higher measured MET value.

These findings highlight a critical underestimation in the quantification of effort during prenatal exercise, which is essential to address to safely prescribe exercise for this unique population.