This study compared 3 d of carbohydrate loading (CHOL; 8.4 g·kg−1·d−1 carbohydrate) in female eumenorrheic athletes with 3 d of an isoenergetic normal diet (NORM; 5.2 g·kg−1·d−1 carbohydrate) and examined the effect of menstrual-cycle phase on performance, muscle-glycogen concentration [glyc], and substrate utilization. Nine moderately trained eumenorrheic women cycled in an intermittent protocol varying in intensity from 45% to 75% VO2max for 75 min, followed by a 16-km time trial at the midfollicular (MF) and midluteal (ML) phases of the menstrual cycle on NORM and CHOL. Time-trial performance was not affected by diet (CHOL 26.10 ± 1.04 min, NORM 26.16 ± 1.35 min; P = 0.494) or menstrual-cycle phase (MF 26.05 ± 1.10 min, ML 26.23 ± 1.33 min; P = 0.370). Resting [glyc] was lowest in the MF phase after NORM (575 ± 145 mmol·kg−1·dw−1), compared with the MF phase after CHOL (728 mmol·kg−1·dw−1) and the ML phase after CHOL and NORM (756 and 771 mmol·kg−1·dw−1, respectively). No effect of phase on substrate utilization during exercise was observed. These data support previous observations of greater resting [glyc] in the ML than the MF phase of the menstrual cycle and suggest that lower glycogen storage in the MF phase can be overcome by carbohydrate loading.
McLay and Thomson are with the Dept of Human Nutrition; Williams, the Dept of Preventive and Social Medicine; and Rehrer, the School of Physical Education and Dept of Human Nutrition, University of Otago, Dunedin, New Zealand.