Some women can train a lot and never disrupt or lose their menstrual cycle, while others notice changes in their cycle with relatively little training. High training volumes, low body weight, and endurance sports like distance running increase the incidence of menstrual irregularities. Many women who train hard and have a low body fat percentage experience irregular or even absent menstrual cycles (amenorrhea), which means a reduced estrogen level. A woman with amenorrhea has about one third the estrogen concentration and about 10 to 20 percent the progesterone concentration of a normal menstruating woman.
"Cessation of the menstrual cycle is not encouraged nor is it a healthy response to training," Mueller says. "Hormonal imbalances over the long term can negatively impact metabolic rate, bone density, immunity, longevity in sports, fertility, and overall athletic performance."
Simply increasing your caloric intake can help reverse amenorrhea, as can cutting back on a hardcore and strict running program.
Training Around Your Cycle
Since your hormones may be to blame if you have a bummer workout, don't beat yourself up over it. The trick is knowing how and when to do which kinds of workouts to maximize your results and get the largest return on your running investment.
"Hit the high intensity in the low-estrogen phases of your cycle, and more endurance-type activities when estrogen is elevated," advises Sims.
If you feel bloated from the rapid drop in progesterone as you transition from the luteal phase to the follicular phase, you may want to avoid high-intensity or long-endurance workouts during those few days. For example, if you have a 28-day cycle starting on Monday, and your period occurs on days 1 to 3 (Monday to Wednesday), plan your hard workout on Thursday or Friday that week.
If you have two hard workouts planned, schedule them on Thursday and Saturday, or schedule just one hard workout the week of your period and two hard workouts during the other three weeks of your cycle. If your period lasts five days (Monday to Friday), schedule one hard workout the week of your period and two hard workouts during the other three weeks of your cycle.
If you want to get the most from your training, understand your cycle and make estrogen work for you. And if you train smart enough, not only will you feel better during your next interval workout, you may even be able to challenge the grunting guy on the treadmill next to you.Sign up for your next race.