Background: Maternal physical activity declines across gestation, possibly due to changing perception of physical activity intensity. Our purpose was to a) determine whether rating of perceived exertion (RPE) during a treadmill exercise changes at a given energy expenditure, and b) identify the influence of prepregnancy physical activity behavior on this relationship.
Methods: Fifty-one subjects were classified as either exercisers (N = 26) or sedentary (N = 25). Participants visited our laboratory at 20 and 32 weeks gestation and at 12 weeks postpartum. At each visit, women performed 5 minutes of moderate and vigorous treadmill exercise; speed was self-selected. Heart rate (HR), oxygen consumption (VO2), and RPE were measured during the last minute at each treadmill intensity.
Results: At moderate intensity, postpartum VO2 was higher compared with 20- or 32-week VO2, but there was no difference for HR or RPE. For vigorous intensity, postpartum HR and VO2 were higher than at 32 weeks, but RPE was not different at any time points.
Conclusions: RPE does not differ by pregnancy time point at either moderate or vigorous intensity. However, relative to energy cost, physical activity was perceived to be more difficult at 32 weeks compared with other time points. Pregnant women, then, may compensate for physiological changes during gestation by decreasing walking/running speeds.