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Metabolism and Muscle Glycogen
Menstrual phase variations in running performance may largely be a consequence of changes to exercise metabolism stimulated by the fluctuations in estrogen and progesterone concentrations. The magnitude of increase in these hormones between menstrual phases and the ratio of estrogen to progesterone concentration appear to be important factors determining an effect on metabolism.
Estrogen may improve endurance performance by altering carbohydrate, fat, and protein metabolism, with progesterone often acting antagonistically to estrogen. Estrogen promotes both the availability of glucose and uptake of glucose into slow-twitch muscle fibers, providing the fuel of choice during short duration exercise.
The ability to run for a long time is greatly influenced by the amount of glycogen stored in your skeletal muscles, with fatigue coinciding with glycogen depletion. Research comparing the amount of muscle glycogen in women eating either a normal diet (2.4 grams of carbohydrate per pound of body weight per day) for three days or a high carbohydrate diet (3.8 grams of carbohydrate per pound of body weight per day) for three days has shown that muscle glycogen content is highest during the mid-luteal phase after both normal and high carbohydrate diets. Muscle glycogen is lowest during the mid-follicular phase.
However, a female runner can increase the amount of muscle glycogen in the follicular phase by eating a high carbohydrate diet. There is also a glycogen-sparing effect to the luteal phase, with a greater reliance on fat during submaximal exercise.
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Theoretically, with less reliance on carbohydrate for energy, less lactate (and, therefore, other metabolic byproducts) is produced. Some studies have documented that less lactate is indeed produced during exercise in the mid-luteal phase, while other studies have not. Interestingly, when men are given a synthetic version of progesterone, they produce less lactate during maximal exercise, suggesting that progesterone, which is elevated during the luteal phase, may lower lactate levels.
Female runners can expect to perform better during times of the menstrual cycle when estrogen is the dominant hormone and perform the worst when progesterone is the dominant hormone. Many of the female runners I’ve coached have experienced their worst training days in the few days leading up to and including menstruation. You may find that while harder workouts may be more challenging during your period, easy running may actually improve your mood and alleviate physical symptoms associated with it.
Avoid challenging workouts around menses, especially if you don’t feel well at that time or if you feel bloated due to the rapid drop in progesterone as you transition from the luteal phase to the follicular phase. For example, if you have a 28-day cycle starting on Monday, and menses occurs on the first three days, plan your hard workout on Thursday or Friday that week. If you have two workouts planned, schedule them on Thursday and Saturday, or schedule just one workout the week of menses and two workouts during the other three weeks of your cycle. If menses lasts five days, schedule one workout the week of menses and two workouts during the other three weeks of your cycle.
About The Author:
Dr. Jason Karp is a nationally-recognized running and fitness expert, 2011 IDEA Personal Trainer of the Year, and owner of RunCoachJason.com. He holds a Ph.D. in exercise physiology. A prolific writer, he has more than 200 articles published in international running, coaching, and fitness magazines, is the author of five books, including Running for Women and Running a Marathon For Dummies, and is a frequent speaker at international fitness and coaching conferences. For his popular training programs and an autographed copy of his books, go to RunCoachJason.com.