The effects of L-carnitine supplementation in different phases of menstrual cycle on the metabolic responses after exhausted exercise in active women

Reports in the literature on the menstruation cycle and its effect on exercise performance are contradictory, while consumption of nutrient supplements by women aiming at enhancing performance is invreasing. The purpose of this study was to investigate the effect of L-carnitine supplementation in the follicular and luteal phases of the menstrual cycle on the aerobic capacity and metabolic responses and performance after exhausted exercise in active women. The study design was a double-blind cross-sectional trial. Twenty-six active volunteer college girl-students, 22.8 ± 3.0 years old, with a regular menstrual cycle with the folowing anthropometric measurements were selected: weight, 56.6±6.0 Kg; height, 163.3±4.0 cm; BMI, 20.8 ± 1.2 kg/m2. They were invited to come to our laboratory 3-9 days (i.e., in the follicular phase) and 18-25 days (i.e., in the luteal phase) after bleeding, at 2 consecutive months. They took either L-carnitine or placebo (40 mg/Kg body weight) capsules 2 hours before the Brunce test. The statistical tests used for data analysis were the one-way ANOVA with repeated measurement for parametric, and the Freidman test for non-parametric, data. The maximal oxygen consumption and time to exhaustion in both follicular and luteal phases increased significantly with L-carnitine supplementation by 5.5% and 6.7% (as compared to placebo), respectively. Also, L-carnitine supplementation in both phases led to a statistically significant decrease in blood lactate accumulation (F3,66 = 5.235, P =0.003); the magnitude of reduction in the follicular phase was 28.2% higher than in the luteal phase. On the other hand, the respiratory ventilation in the luteal phase increased significantly with L-carnitine supplementation (15% higher compared to the follicular phase). L-carnitine supplementation in the follicular phase, when estrogen is at its minimal level, can help decrease a reduction in VO2max and excrcise performance. The increased serum L-carnitine level may cause an increase in ß-oxidation and, thereby, increase VO2max and enhance performance.