EFFECT OF REGULAR EXERCISE ON RATINGS OF PERCEIVED EXERTION DURING PREGNANCY

Abstract

A woman's heart rate (HR) response to exercise changes over the course of pregnancy. However, it is less clear how her perception of effort required during physical exertion relates to HR and energy expenditure, and if these relationships are moderated by regular physical activity. It was our purpose to determine the relationship between maternal Ratings of Perceived Exertion (RPE) with HR and energy expenditure (measured as VO2) during exercise. METHODS Study articipants were either regular exercises (n = 27) or sedentary control (n = 25) women, recruited in early pregnancy. Women were tested twice during pregnancy (20 and 32 wks) and again 12 weeks postpartum. Each woman walked or ran continuously on a motorized treadmill over three, five-minute incremental exercise stages. Expired respiratory gases and HR were measured continuously. RPE was measured at the end of each treadmill stage using a 15 point Borg scale. Regression lines for the relationships between RPE vs HR, and RPE vs VO2, were calculated for each woman for each testing occasion. Slopes and y-intercepts were tested using mixed design (group vs pregnancy state) ANOVA. RESULTS There were significant (P < 0.01) main effects of group and pregnancy state for the slope of RPE vs HR, but no interaction between the two conditions. Specifically, change in RPE for a given change in exercise HR was greater in sedentary women (0.14 vs 0.12), and change in RPE was greater during pregnancy (0.13 and 0.15) compared to postpartum (0.10), regardless of exercise behavior. In contrast, in addition to showing significant main effects (P < 0.01), exercise training and pregnancy state interacted with respect to the slope of the RPE vs VO2 regression. At 32 weeks gestation, sedentary women showed greater change in RPE for a given VO2 (0.71) compared to any other condition (0.42–0.53). There were no significant differences in y-intercept in any test condition. CONCLUSIONS Pregnancy heightens a woman's perception of effort required to perform incremental aerobic exercise. This change in perception appears to be blunted in chronic exercisers who remain active throughout gestation. These results have important ramifications when considering how to estimate intensity levels of maternal exercise programs at different stages of pregnancy. Supported by NIH 08-R3HD35080A