Menstrual Cycle. Sex and exercise the science behind it
Menstrual cycle. Why a woman’s primary sex hormone estrogen, is the single biggest thing that influences everything from metabolism to muscle glycogen storage to bone health.
Testosterone in women
Don’t want big, manly muscles? Don’t worry! Women have up to 20 times less testosterone as men. (Before puberty, testosterone level is similar between the sexes, which is why young girls can often run and jump just as fast and as far as boys.) Your testosterone is highest around age 20 and is half as high in your 40s. If you recently met the man of your dreams, you’re in luck: research shows that falling in love increases women’s testosterone level (but it returns to your normal level after the honeymoon stage of the relationship). As in men, testosterone in women stimulates sexual desire, increases libido, heightens arousal, and increases sexual satisfaction. It’s also important for bone strength and development of lean muscle mass and strength.
A few minutes into your high-intensity intervals, you notice your legs feel sluggish. “That’s odd,” you think since you felt fine just a few days earlier. You shrug it off as just a bad day at the gym and return the next week to do another interval workout. After the first sprint, you can’t believe how good your legs feel. You try another, thinking it may just be a fluke. Again, you feel like you’re flying, like the treadmill belt can’t keep up with you! “How can this be?” you ask yourself. “Just last week I felt so sluggish!” Overhearing your conversation with yourself, a woman on the treadmill next to you whispers as if she were describing a disease, “It’s estrogen.”
Your primary sex hormone, estrogen is the single biggest thing that differentiates you from that guy grunting during bench presses at the gym. It’s a powerful hormone, influencing everything from metabolism to muscle glycogen storage to bone health. Indeed, estrogen is so important to bones that its deficiency, often caused by irregular or absent menstruation from a high level of training and not consuming enough calories, is the most significant risk factor for osteoporosis inactive women.
While your hubby’s or boyfriend’s hormonal environment is pretty stable (don’t you hate that?!), your hormonal environment is constantly changing. The levels of estrogen and its sister hormone progesterone change continuously throughout your menstrual cycle, which occurs monthly from menarche (age 11- 14) until menopause (age 45-50).
Although your menstrual cycle is complicated, an easy way to think of it is that the first 2 weeks (follicular phase) begins with your period and is dominated by estrogen, and the second 2 weeks (luteal phase) begins with ovulation and is dominated by progesterone, although estrogen is also elevated in the middle of the luteal phase. The luteal phase ends with the start of your period, and the cycle starts all over again.
In general, you can expect to feel better and have better workouts during times of the month when estrogen is the dominant hormone and feel the worst during your period and when progesterone is the dominant hormone. And you may find that, while harder workouts may be more challenging during your period, easy workouts may actually improve your mood and alleviate physical symptoms associated with your period. But there’s a lot of variability between women. Keep a menstrual log to determine how your menstrual cycle affects you and your training.
Perhaps the most significant effect of estrogen is a shift in your metabolism during submaximal aerobic exercise to a greater reliance on fat, which spares your muscles’ limited store of carbohydrate. By sparing the amount of carbohydrate used and relying more on fat for energy, fatigue is delayed and your endurance is improved. And because your muscles use less carbohydrate during exercise, they also use less protein, since protein only provides significant energy for muscle contraction when muscle glycogen is low.
Since muscular strength and power are proportional to muscle size, you can’t get as strong or as powerful as your boyfriend or hubby since men typically have bigger muscles and more testosterone to make those muscles even bigger. But you can cheat the system a bit if you alter your training based on your hormones and capitalize on being a woman. Although you’re not any stronger at certain times of the month than you are at any other, your menstrual cycle can influence how you respond to your workouts. The fluctuations in estrogen and progesterone throughout your menstrual cycle alter the ability to build muscle and recover. For example, a study in International Journal of Sports Medicine found that weight training with 3 sets of 12 reps every second day during the follicular phase of the menstrual cycle and once per week during the luteal phase increased maximal quadriceps strength by 32.6 percent compared to just 13.1 percent by training once every third day over the whole menstrual cycle. It seems that doing more training in the estrogen-dominant follicular phase and less training in the progesterone-dominant luteal phase leads to greater strength gains. Estrogen rocks!
Your menstrual cycle also influences your muscles’ sensitivity to storing carbohydrate as fuel. From the mid-follicular to mid-luteal phase of your cycle (day 6 to day 20), women can take advantage of the body’s increased storage of carbohydrate and consequent favorable conditions for enhanced muscular endurance during aerobic and high-intensity workouts. During the early follicular phase and late luteal phase, glycogen stores decrease and endurance wanes. Nutrition is importance in these phases because with less carbohydrate, there’s greater protein breakdown and suppression of the immune system. Focus on consuming more immune-enhancing ingredients such as probiotics (yogurt), antioxidants (fruits, vegetables, green tea, and wheat germ), and vitamin D (tuna, eggs, fortified dairy foods, pork loin, wild salmon, and mushrooms).
Many women who train hard and train a lot who have a low body fat percentage often experience irregular or even absent menstrual cycles, which reduces estrogen levels. Amenorrhea (0 to 3 periods per year) causes constant low levels of estrogen and progesterone. 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.
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. Although a very low body fat percentage is desirable if you want to look good or compete in certain sports, it can negatively impact your menstrual cycle and your health.
Research shows that inadequate caloric intake to match caloric expenditure, rather than the stress of exercise, is responsible for the loss of menstrual activity and that consuming more calories to compensate for the large caloric expenditure from exercise can prevent amenorrhea.
Training around your cycle
To paraphrase a well-known antiperspirant commercial, your training program is strong enough for a man but made for a woman. The principles of strength training to increase muscle definition or aerobic training to increase endurance or sprint training to increase speed and power are the same for both sexes. The differences, however, lie in the program’s subtleties. Unlike your boyfriend’s or hubby’s training program, your training program incorporates more adjustments based on fluctuations of hormones and other female-specific conditions, like amenorrhea and pregnancy.
If you have a bad workout, don’t beat yourself up over it. There are probably female-specific reasons why you had a bad workout, including the physical influence of your menstrual cycle, the emotional influence of hormones, or the psychological stresses of motherhood. The “secret” is knowing how and when to manipulate your workouts to optimize your training and maximize your results so you can get the largest return on your investment. For example, do highintensity workouts in the lower hormone phases of your cycle, and endurance workouts when estrogen is elevated.
If you don’t feel well during your period or 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 challenging 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 2 hard workouts planned, schedule them on Thursday and Saturday, or schedule just 1 hard workout the week of your period and 2 hard workouts during the other 3 weeks of your cycle. If your period lasts 5 days (Monday to Friday), schedule 1 hard workout the week of your period and 2 hard workouts during the other 3 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!
Jason R. Karp, Ph.D.