Thermoregulatory and metabolic responses to jogging prior to and during pregnancy

Ten joggers were serially studied prior to and during pregnancy at their individual training intensity levels to estimate their thermal and metabolic response to exercise in the field. Prior to conception, a 20-min run at 74% of VO2max (range = 62 to 90%) increased the respiratory exchange ratio to 0.90 +/- 0.01 (range = 0.87 to 0.96) with a rise in whole blood glucose (5.19 +/- 0.14 to 6.63 +/- 0.23 mM X l-1), lactate (0.61 +/- 0.06 to 2.62 +/- 0.74 mM X l-1), and rectal temperature (37.5 +/- 0.1 to 39.0 +/- 0.1 degree C). Despite a spontaneous decrease in exercise intensity to 57 +/- 5% of VO2max (range = 34 to 79%) at 20 and to 47 +/- 2% of VO2max (range = 36 to 59%) at 32 wk gestation, the rise in respiratory exchange ratio with exercise was maintained at 0.92 +/- 0.02 (range = 0.88 to 0.97) and 0.93 +/- 0.01 (range = 0.88 to 0.97), respectively, suggesting a shift to the left in the relationship between exercise intensity and fractional carbohydrate utilization by muscle during exercise in pregnancy. The concomitant changes in whole blood glucose before and after exercise at 20 (4.46 +/- 0.16 to 4.45 +/- 0.08 mM X l-1) and 32 (5.30 +/- 0.19 to 4.55 +/- 0.15 mM X l-1) wk further strengthen this view. Post-exercise, whole blood lactate levels at 20 (0.53 +/- 0.06 to 1.59 +/- 0.30 mM X l-1) and 32 (0.77 +/- 0.07 to 0.89 +/- 0.11 mM X l-1) wk were lower than those observed prior to pregnancy.(ABSTRACT TRUNCATED AT 250 WORDS)