Carbohydrate-loading during the follicular phase of the menstrual cycle: effects on muscle glycogen and exercise performance.
The effects of employing a high-carbohydrate diet (carbohydrate-loading) to increase glycogen storage in skeletal muscle are not well established in female athletes. On 4 occasions--2 familiarization trials and 2 experimental trials--6 well-trained female subjects completed 6 x 15-min continuous intervals of cycling (12 min at 72% VO2max, 1 min at maximal effort, and 2 min at 50% VO2max), followed by a time trial 15 min later. The women consumed their habitual diets (HD; 6-7 g carbohydrate/kg lean body mass) for 3 days after the second familiarization trial and before the first experimental trial. During the 3 days following the first experimental trial, the subjects consumed a high-carbohydrate diet (CD; 9-10 g carbohydrate/kg lean body mass) prior to the second experimental trial. Mean (+/-SEM) pre-exercise muscle glycogen concentrations were greater after CD versus HD (171.9+/-8.7 vs. 131.4+/-10.3 mmol/kg wet weight, P < 0.003). Although 4 of the 6 subjects improved their time-trial performance after CD, mean performance for the time trial was not significantly different between diets (HD: 763.9+/-35.6 s; CD: 752.9+/-30.1 s). Thus, female cyclists can increase their muscle glycogen stores after a carbohydrate-loading diet during the follicular phase of the menstrual cycle, but we found no compelling evidence of a dietary effect on performance of a cycling time trial performed after 90 min of moderate-intensity exercise.
Paul
D R
DR
Diet and Human Performance Laboratory at the Beltsville Human Nutrition Research Center, ARS, USDA, MD 20705, USA.
Mulroy
S M
SM
Horner
J A
JA
Jacobs
K A
KA
Lamb
D R
DR
D001642:Bicycling; D001786:Blood Glucose / Q000032:analysis; D004040:Dietary Carbohydrates / Q000008:administration & dosage*; D015444:Exercise / Q000502:physiology*; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005260:Female; D005498:Follicular Phase / Q000378:metabolism / Q000502:physiology*; D006003:Glycogen / Q000096:biosynthesis*; D006801:Humans; D007328:Insulin / Q000097:blood; D019344:Lactic Acid / Q000097:blood; D018482:Muscle, Skeletal / Q000378:metabolism*; D010101:Oxygen Consumption; D013997:Time Factors
D001786:Blood Glucose; D004040:Dietary Carbohydrates; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D019344:Lactic Acid; D006003:Glycogen