Objective: This study aims to compare maternal and fetal responses during two physical exercise types. Design:A randomized clinical trial compared 120 pregnant women, gestational age of 35-37 weeks, 56 exercising on a stationary bicycle (Group A) and 64 on a treadmill (Group B). Methods:Participants were monitored for three 20-minute phases:resting, exercise and recovery. Fetal heart rate (FHR) and maternal heart rate (MHR) were monitored. Glucose and lactate levels were evaluated at rest and during exercise. Results:After the beginning of exercise, maximum lactate (L) levels were reached at 20 minutes and never exceeded 4 mmol/l. FHR decreased by 22 bpm during exercise in relation to resting values, irrespective of the exercise type (p<0.001). Comparing the exercise types, the incidence of bradycardia after 10' was 23.2% in Group A and 35.9% in Group B (p>0.05), increasing at 20' to 32% and 40.6%, respectively, (p>0.05). The FHR decrease during exercise was accompanied by a simultaneous increase in its variability (p<0.001), nevertheless a rapid return to resting values was observed shortly after exercise end. Glucose decreased in both groups irrespective of the exercise type (85 mg/dl at rest; 79 mg/dl during exercise and 81 mg/dl during recovery; p<0.001). There were no hypoglycemia cases.Conclusions: FHR variability increase and the rapid return to resting values after exercise suggests that the FHR fall and the presence of bradycardia during exercise is the fetal physiologic response to blood flow redistribution, with maintenance of fetal well-being.

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