PT on the Net Research

Estrogen, Menstrual Cycle, and Exercise


A few minutes into your client’s high intensity intervals, she notices her legs feel sluggish. “That’s odd,” she thinks, since she felt fine just a few days earlier. She shrugs it off as just a bad day at the gym, and returns the next week to do another interval workout. After the first sprint, she can’t believe how good her legs feel. She tries another, thinking it may just be a fluke. Again, she feels like she’s flying, like the treadmill belt can’t keep up with her. “How can this be?” she asks herself. “Just last week I felt so sluggish!” Overhearing her conversation with herself, a woman on the treadmill next to her whispers as if she were describing a disease, “It’s estrogen, dear.”  

Learning Objectives:

  1. To understand the estrogen-specific issues related to training female clients.
  2. To show how and why women should train differently than men.
  3. To explain how women can manipulate their training around their menstrual cycle.

A woman’s primary sex hormone, estrogen is the single biggest thing that differentiates a woman 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 in active women.

While a man’s hormonal environment is pretty stable, a woman’s hormonal environment is constantly changing. The levels of estrogen, and its sister hormone progesterone, change continuously throughout the menstrual cycle, which occurs monthly from menarche (age 11 to 14) until menopause (age 45 to 50).

Although the menstrual cycle is complicated, an easy way to think of it is that the first two weeks (follicular phase) begins with the woman’s period and is dominated by estrogen, and the second two 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 the period, and the cycle starts all over again.

In general, a woman 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 her period and when progesterone is the dominant hormone (Karp & Smith, 2012). And she may find that, while harder workouts may be more challenging during her period, easy workouts may actually improve her mood and alleviate physical symptoms associated with her period. But there’s a lot of variability between women. While some women may have few noticeable effects during their cycles, others may notice fatigue, difficulty working out in hot weather, cramping, bloating, and increased perception of effort, particularly in the days leading up to and the first few days of their period.

Metabolism

Perhaps the most significant effect of estrogen is a shift in metabolism to a greater reliance on fat and a lesser reliance on carbohydrate during submaximal aerobic exercise compared to men (Tarnopolsky, 1998). Because the ability to exercise is influenced by the amount of glycogen in muscles, by sparing the amount used and relying more on fat for energy, fatigue is delayed and endurance is improved. Because a woman’s 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.

Muscular Strength

Since muscular strength and power are proportional to muscle size, a woman can’t get as strong or as powerful as her boyfriend or hubby since men typically have bigger muscles and up to 20 times more testosterone to make those muscles even bigger. (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.) In women, testosterone is highest around age 20 and is half as high in her 40s.

To get stronger, a woman can cheat the system a bit if she alters her training based on her hormones and capitalizes on being a woman. Although a woman is not any stronger at certain times of the month than she is at any other, her menstrual cycle can influence how she responds to her workouts. The fluctuations in estrogen and progesterone throughout the menstrual cycle alter the ability to build muscle and recover from workouts. For example, Reis et al. (1995) 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.

Muscle Glycogen

The menstrual cycle also influences muscles’ sensitivity to storing carbohydrate as fuel. From about day 6 to day 20 of the cycle (mid-follicular to mid-luteal phase), women can take advantage of the body’s increased storage of carbohydrate and consequent favorable conditions for enhanced muscular endurance during both aerobic and high-intensity workouts. Nutrition becomes of paramount importance in these phases because with less carbohydrate, there’s greater protein breakdown and suppression of the immune system. Women should focus on consuming more immune-enhancing ingredients such as probiotics (low-fat kefir and yogurt), antioxidants (green tea, fruits, vegetables, and wheat germ), and vitamin D (wild salmon, tuna, pork loin, eggs, fortified dairy foods, and mushrooms).

Menstrual Irregularities

Many women who train hard, train often, and who have a low body fat percentage often experience irregular or even absent menstrual cycles, which reduces estrogen levels. Amenorrhea (defined as 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 to look good and for performance of many athletic activities, it can negatively impact a woman’s menstrual cycle and health.

Inadequate caloric intake to match caloric expenditure, rather than the stress of exercise, is responsible for the loss of menstrual activity (Williams et al., 2001). Consuming more calories to compensate for the large caloric expenditure from exercise can prevent amenorrhea.

Training around the Cycle

To paraphrase a well-known antiperspirant commercial, a woman’s training program should be 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 a man’s training program, a woman’s training program should incorporate more adjustments based on fluctuations of hormones and other female-specific conditions, like amenorrhea and pregnancy. The secret of a woman’s training program is knowing how and when to manipulate her workouts to optimize her training and maximize her results so she can get the largest return on her investment.

Women should hit the high-intensity workouts in the lower hormone phases of her cycle, and more endurance-type activities when estrogen is elevated. They should also increase consumption of quality protein before and after training during times of elevated progesterone because progesterone is catabolic, which reduces the body’s ability to recover and build muscle.

If a woman doesn’t feel well during her period or if she feels bloated from the rapid drop in progesterone as she transitions from the luteal phase to the follicular phase, she may want to avoid challenging workouts during those few days. For example, with a 28-day cycle starting on Monday and the period occurring on days 1 to 3 (Monday to Wednesday), plan the hard workout on Thursday or Friday that week. If two hard workouts are planned, schedule them on Thursday and Saturday, or schedule just one hard workout the week of the period and two hard workouts during the other three weeks of the cycle. If the period lasts five days (Monday to Friday), schedule one hard workout the week of the period and two hard workouts during the other three weeks of the cycle.

Conclusion

For your female clients to get the most from their workouts, understand their cycle and make estrogen work for them. And if they train smart enough, not only will they feel better during their next interval workout, they may even be able to challenge the grunting guy on the treadmill next to them.

References

Karp, J.R. & Smith, C.S. (2012). Running for women. Champaign, IL: Human Kinetics.

Reis, E., Frick, U., & Schmidtbleicher, D. (1995). Frequency variations of strength training sessions triggered by the phases of the menstrual cycle. International Journal of Sports Medicine, 16(8), 545-550.

Tarnopolsky, M.A. (1998). Gender differences in lipid metabolism during exercise and at rest. In M.A. Tarnopolsky (Ed.). Gender Differences in Metabolism: Practical and Nutritional Implications. Boca Raton, FL: CRC Press.

Williams, N.I., Helmreich, D.L., Parfitt, D.B., Caston-Balderrama, A., & Cameron, J.L. (2001). Evidence for a causal role of low energy availability in the induction of menstrual cycle disturbances during strenuous exercise training. Journal of Clinical Endocrinology and Metabolism, 86, 5184-5193.