Glucose kinetics and substrate oxidation during exercise in the follicularand luteal phases

The purpose of this investigation was to determine whether plasma glucose k inetics and substrate oxidation during exercise are dependent on the phase of the menstrual cycle. Once during the follicular (F) and luteal (L) phase s, moderately trained subjects [peak O-2 uptake ((V) over dot (O2)) = 48.2 +/- 1.1 ml . min(-1) . kg(-1); n = 6] cycled for 25 min at similar to 70% o f the ire, at their respective lactate threshold (70%LT), followed immediat ely by 25 min at 90%LT. Rates of plasma glucose appearance (R-a) and disapp earance (R-d) were determined with a primed constant infusion of [6,6-H-2]g lucose, and total carbohydrate (CHO) and fat oxidation were determined with indirect calorimetry. At rest and during exercise at 70%LT, there were no differences in glucose R-a or R-d between phases. CHO and fat oxidation wer e not different between phases at 70%LT. At 90%LT, glucose R-a (28.8 +/- 4. 8 vs. 33.7 +/- 4.5 mu mol.min(-1). kg(-1); P < 0.05) and R-d (28.4 +/- 4.8 vs. 34.0 +/- 4.1 <mu>mol . min(-1) . kg(-1); P < 0.05) were lower during th e L phase. In addition, at 90%LT, CHO oxidation was lower during the L comp ared with the F phase (82.0 +/- 12.3 vs. 93.8 +/- 9.7 <mu>mol . min(-1) . k g(-1); P<0.05). Conversely, total fat oxidation was greater during the L ph ase at 90%LT (7.46 +/- 1.01 vs. 6.05 +/- 0.89 <mu>mol . min(-1) . kg(-1); P < 0.05). Plasma lactate concentration was also lower during the L phase at 90%LT concentrations (2.48 +/- 0.41 vs. 3.08 +/- 0.39 mmol/l; P < 0.05). T he lower CHO utilization during the L phase was associated with an elevated resting estradiol (P < 0.05). These results indicate that plasma glucose k inetics and CHO oxidation during moderate-intensity exercise are lower duri ng the L compared with the F phase in women. These differences may have bee n due to differences in circulating estradiol.