The effect of the menstrual cycle and hyperglycaemia on hormonal and metabolic responses during exercise

Abstract

Purpose: Variations in substrate metabolism have been identified in women during continuous steady-state aerobic exercise performed at the same relative intensity throughout discrete phases of the menstrual cycle, although some evidence exists that this is abolished when carbohydrate is ingested. This investigation examined the effects of a supraphysiologic exogenous glucose infusion protocol, administered during two phases of the menstrual cycle (follicular and luteal) in eumenorrheic women to identify differences between metabolic, hormonal and substrate oxidative responses.

Methods: During the experimental conditions, blood glucose was infused intravenously at rates to "clamp" blood glucose at 10 mM in seven healthy females (age 20 ± 1 y, mass 55.0 ± 4.1 kg, [Formula: see text] 40.0 ± 1.8 ml/kg/min). Following 30 min of seated rest, participants exercised on a cycle ergometer for 90 min at 60% [Formula: see text]. During the rest period and throughout exercise, blood metabolites and hormones were collected at regular intervals, in addition to expired air for the measurement of substrate oxidation.

Results: Significant differences between ovarian hormones and menstrual phase were identified, with estrogen significantly higher during the luteal phase compared to the follicular phase (213.28 ± 30.70 pmol/l vs 103.86 ± 13.85 pmol/l; p = 0.016), and for progesterone (14.23 ± 4.88 vs 2.11 ± 0.36 nmol/l; p = 0.042). However, no further significance was identified in any of the hormonal, metabolite or substrate utilisation patterns between phases.

Conclusion: These data demonstrate that the infusion of a supraphysiological glucose dose curtails any likely metabolic influence employed by the fluctuation of ovarian hormones in eumenorrheic women during moderate exercise.

Keywords: Estrogen; Follicular; Glucose infusion; Luteal; Moderate exercise; Progesterone.

Fig. 1

Mean (± SEM) A Plasma glycerol, B serum NEFA and C plasma lactate concentration during the follicular and luteal Phases. *significantly lower than at − 30 min, #significantly greater than at − 30 and 0 min, †significantly greater than at 15 min, ψ significantly greater than at 30 min, **significantly greater than at − 30 and 0 min

Fig. 2

Mean (± SEM) serum progesterone and estrogen concentrations. *significantly greater than in the follicular phase p < 0.05

Fig. 3

Mean (± SEM) A serum insulin concentration, B serum cortisol and C HGH concentration during the follicular and luteal phases. *significantly greater than at − 30 min, #significantly greater than at 30 min, †significantly greater than at 0 min

Fig. 4

Mean (± SEM) A lipid oxidation rate B carbohydrate oxidation rate and C glucose utilisation rate during the follicular and luteal Phases. *significantly greater than at − 30 and 0 min, **significantly greater than at 0 and 15 min

Fig. 5

The percentage contribution of substrates to total substrate oxidation using pooled data from both phases