No changes during pregnancy in the net cost of cycling exercise.

OBJECTIVE: To investigate whether work efficiency improves during pregnancy. DESIGN: Longitudinal; energy expenditure measurements (ventilated hood system) before the onset of pregnancy and in weeks 13, 24 and 35 of gestation. SUBJECTS: Healthy Dutch women (n = 26), recruited with advertisements in local newspapers and posters displayed in public buildings. MAIN OUTCOME MEASURES: Resting metabolic rate (RMR); metabolic rate during cycling at workloads of 30, 45, 60 and 75 W (CMRgross); post-cycling metabolic rate (PCMRgross); net energy costs of cycling (CMRnet = CMRgross - RMR); net recovery costs after cycling exercise (PCMRnet = PCMRgross - RMR). RESULTS: RMR, CMRgross and PCMRgross increased during pregnancy; under all conditions, metabolic rates were 0.9 kJ/min higher at 35 weeks gestation than before pregnancy (P < 0.05). CMRnet and PCMRnet showed no significant change during gestation. CONCLUSIONS: Changes in metabolic rate during cycling exercise suggest that pregnancy does not induce an improvement of work efficiency.