[Study on anaerobic threshold in normal pregnant women]

We evaluated the anaerobic threshold (AT) in 104 normal pregnant women mainly in their second trimester. Each exercise testing was performed by using incremental bicycle ergometry at a pedal frequency of 60rpm while monitoring maternal heart rate, maternal blood pressure, minute ventilation (VE),oxygen uptake (VO2) and carbon dioxide output (VCO2) every 30 seconds. The AT was determined by estimating the point of departure from linearity of the plot of VE as a function of VO2. We could determine the AT in 100 cases (96.2%), and their AT values and the heart rates at AT point were 14.7 +/- 1.7ml/min/kg (mean +/- S.D.) and 128 +/- 12bpm, respectively. AT decreased significantly (p < 0.01) with the length of gestation, because of increased maternal body weight. The heart rate at the AT also declined significantly (p < 0.05) with gestational age, but it had no relation with maternal body weight. These results show that the maternal heart rate becomes hard to increase with gestational age, so that the maximal heart rate, as an index of exercise intensity during exercise should decrease with advancing gestational age.