By Jason R. Karp, PhD, MBA
Adapted from the book Running Periodization: Training Theories to Run Faster, by Dr. Karp. This is the third article in this series.
“Understanding the menstrual cycle is the key to unlocking the female runner’s training secret.”
Atalanta, the Greek goddess of travel and adventure, was known for her athletic prowess that rivaled that of most men. Warned against marriage by an oracle, Atalanta came up with a plan to marry only a suitor who could beat her in a race, killing those who failed to outrun her. “I am not to be won till I be conquered first in speed. Wife and couch shall be given as prize unto the swift, but death shall be the reward of those who lag behind,” she exclaimed in the Roman poet Ovid’s Metamorphoses.
Many would-be suitors were beaten until Hippomenes fell in love with Atalanta and wanted to marry her. When hearing of the challenge, he was skeptical, but when Atalanta took off her outer garments for her next race, that was all he needed to send in his race entry. There was one problem, however. He knew he could not beat Atalanta, so he asked for help from—who else?—Aphrodite, the goddess of love. Aphrodite provided Hippomenes with three golden apples to drop on the race course to distract Atalanta. During the race, whenever Atalanta pulled ahead of Hippomenes, he rolled one of the golden apples off the course, tempting a curious Atalanta to stop and pick up the apple. Atalanta’s frequent stops to fetch the apples were just enough for Hippomenes to win the race and Atalanta’s hand in marriage.
While men have been running for as long as physical labor has been deemed masculine and heroic, running was not considered an appropriate female activity for most of the 20th century. We now know better. In fact, when it comes to distance running, women can be quite good.
Ever notice that women and girls tend to be able to run for long periods of time, even be able to hold a solid pace for a while, but they often lag behind when running fast for short bursts? There are exceptions, of course, as there always are in sport, and in the rest of life, but, on average, females tend to be better at long endurance than at either sprinting or short endurance (800 meters and 1,500 meters/mile).
From the time we are boys and girls, it is evident there are many differences between males and females. Many of these differences—anatomical, muscular, physiological, hormonal, and metabolic—influence girls’ and women’s running abilities, race performances, and responses to training.
Women and men are even more different than we think: More than 3,000 genes are expressed differently between the muscles of females and males. Scientific research has revealed that there seem to be two main reasons why females are so good at endurance: (1) estrogen, which shifts muscle metabolism toward a greater reliance on fat as fuel and hastens muscle repair and recovery, and (2) proportion of slow-twitch muscle fibers, which are better suited for aerobic endurance than the more powerful, anaerobic fast-twitch fibers.
Muscle biopsy research on the vastus lateralis (the largest of the quadriceps muscles) has shown that women have 35 percent more slow-twitch fibers, 30 percent less fast-twitch A fibers, and 15 percent less fast-twitch B fibers compared to the vastus lateralis of men. Another study showed that the average fiber type percentages in the female vastus lateralis muscle are 41 percent slow-twitch, 36 percent fast-twitch A, and 23 percent fast-twitch B, whereas men have 34 percent slow-twitch, 46 percent fast-twitch A, and 20 percent fast-twitch B. The area the fibers take up in the muscle is also different between females and males: Slow-twitch fibers account for 44 percent of the area in women and 36 percent in men, and fast-twitch A fibers account for 34 percent of the area in women and 41 percent in men. The more slow-twitch muscle fibers in women make female muscles less fatigable than male muscles.
Given the metabolic and muscle fiber differences between females and males, it does appear that women, in general, have a greater capacity for aerobic endurance and long-distance running. My experience as a coach of female runners for many years tells me the same thing. Once in a while, you come across a female distance runner who is better at the middle distances (800 and 1,500 meters/mile) than at the longer distances, but, when looking at a cross-section of the population, it is much more common for females to be better at the longer distances. Of note is the narrowing in performance differences between females and males as the race distance gets longer, especially beyond a marathon. At the elite level, there is a 13.1 percent difference in the men’s and women’s world records for one mile and a 12.1 percent difference for 5K, but only a 10.2 percent difference for the marathon and a 6.5 percent difference for 100K ultramarathon. In 2002 and 2003, ultramarathon runner Pam Reed showed how good women can be at long races by winning the 135-mile (217K) Badwater Ultramarathon, beating all the men. Research is revealing that female ultramarathon runners seem to have a greater resistance to fatigue than do equally trained men whose performances are superior up to the marathon distance.
Among all the differences between females and males, perhaps the greatest female-specific implication for training is the menstrual cycle, which is the defining physiological characteristic of females. The menstrual cycle occurs monthly from a woman’s first period (called menarche; age 11 to 14) until menopause (age 45 to 50). It used to be taboo to talk about the menstrual cycle. It sometimes still is. It’s not often talked about at the dinner table, and hardly ever by a coach. In the 1800s, doctors in Europe and North America thought physical activity would make a woman’s uterus fall out. As a result, women were not allowed to run races. After women’s distance running was introduced at the Olympics in 1928, the visible exhaustion of some of the women at the end of the 800 meters was taken as affirmation that distance running was too dangerous for women, and it was dropped from the Olympics until 1960. We’ve come a long way since then. Women compete in many athletic events. And women run marathons without their uteruses falling out.
It’s hard to suddenly talk openly as an adult about a subject that we’ve learned for years to be so silent about. But understanding the menstrual cycle is the key to unlocking the female runner’s training secret.
Female Physiology
The two major sex hormones of the menstrual cycle—estrogen and progesterone—change continuously throughout the cycle, as a complex interaction of positive and negative feedback mechanisms regulate the timing and amount of hormone secretion. With the large fluctuations in the levels of these hormones, the phases of the menstrual cycle significantly affect the female runner’s hormonal environment, and, therefore, her physiology. Variables such as oxygen consumption, body temperature, lung function, hydration, muscle glycogen storage, fat and carbohydrate metabolism, and exercise performance are all affected by the menstrual cycle.
A textbook menstrual cycle is 28 days (but can last up to 35 days) and is divided in half by ovulation on day 14, as the ovum (egg) is released from the ovary. Although the menstrual cycle is complicated, an easy way to think of it is that the first half—the follicular phase—begins with the period and is dominated by estrogen; the second half—the 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 over again.
The follicular phase typically lasts 14 days but can last 11 to 21 days. (If you’re doing the math, that means that when the cycle is shorter or longer than 28 days, the difference is because of a shorter or longer follicular phase.) Following the period, which typically lasts 3 to 5 days, estrogen rises, peaking around day 14, right before ovulation, when it is 10 times the level it was at the beginning of the follicular phase. During the follicular phase, progesterone remains low.
The luteal phase always lasts 14 days. Progesterone rises after ovulation, while estrogen drops before rising again toward the middle of the phase. The increase in progesterone, which, at its peak in the middle of the luteal phase, is 25 times the level it was during the follicular phase, causes body temperature to increase to prepare for the fertilization of an egg. If fertilization does not occur, both estrogen and progesterone levels decrease abruptly in the second half of the luteal phase.
The exact duration of the menstrual cycle can vary from woman to woman, a cycle to cycle, and year to year. Changes in hormone levels can also affect the duration of the cycle, as it does in teenagers and women in their forties nearing menopause, who tend to have low or changing progesterone levels. Birth control pills, a low percentage of body fat, weight loss, being overweight, stress, and intense exercise can also change the cycle duration.
Menstrual Irregularities
In a perfect physiological environment, your athletes’ menstrual cycles will occur every month and always be the same duration. But that doesn’t always happen, especially among many girls and women who train with high volumes and high intensities and have a low percentage of body fat. They often experience irregular or even absent menstrual cycles, which reduce estrogen levels.
Girls who start intense training before their first period delay their menstruation nearly a year later than girls who already have menstrual periods when they start training. Once menstrual activity starts, its continued occurrence is also sensitive to training. In response to heavy training, the first change in the menstrual cycle is a shortening of the luteal phase, followed by cycles without ovulation, and, finally, cessation of menses, called amenorrhea, which is defined as having three or fewer periods per year, and results in constantly low levels of estrogen and progesterone. A female runner with amenorrhea has about one-third the estrogen concentration and about 10 to 20 percent the progesterone concentration of a normally menstruating woman. Thus, endocrinologically, an amenorrheic runner experiences an estrogen-deficient state similar to that of a postmenopausal woman.
The incidence of menstrual irregularity or amenorrhea varies from woman to woman. Some female runners can train at high volumes and never disrupt or lose their menstrual cycle, while other women notice changes in their cycles with relatively little training. Long-distance runners, in particular, are at an increased risk for menstrual irregularity or amenorrhea, in large part due to the enormous number of calories that are burned from running high volume. However, consuming fewer calories than what is burned, rather than the stress of exercise itself, is responsible for the loss of the menstrual cycle. Consuming enough calories to replace the calories burned from running can prevent amenorrhea. Therefore, if your athletes run a lot, they need to increase the number of calories they consume throughout the day to keep up with the large number of calories they burn by running.
One of the biggest consequences of menstrual irregularity or amenorrhea is poor bone health. Estrogen is extremely important in facilitating the absorption of calcium into bones. Any disruption to the menstrual cycle can cause a decrease in bone density, increasing the risk for osteoporosis and stress fractures, which can occur with only minimal impact to the bones. Female runners with irregular or absent menstruation have significantly lower bone density than runners with regular menstruation and even compared to nonathletes, particularly at the lumbar spine.
How should your athletes train when they don’t have a period, or if their menstrual cycle is irregular? An irregular menstrual cycle makes planning the training more complicated than when not having a menstrual cycle at all, because you can’t predict the months they will have a normal cycle and the months they won’t, unless their cycle is regularly irregular and therefore predictable. If their cycle is irregularly irregular, you need to plan the training month-to-month or even week-to-week. With no menstrual cycle, they can train without consideration to the hormonal environment, since estrogen and progesterone won’t fluctuate throughout the month. It’s perfectly okay to run a lot without a menstrual cycle (plenty of girls and women do). However, in the face of a lack of bone-protecting estrogen, you need to take extra precaution in regard to their bone health, especially if they run a lot. It’s a good idea to regularly get their bone density evaluated as part of an annual medical check-up to determine whether or not they’re at risk for a running-related stress fracture. Strategies like meticulously-planned training that avoids rapid increases in volume and intensity, calcium and vitamin D supplements, oral contraception to provide estrogen, and intense strength training to increase bone density can all help mitigate the risk for bone injuries.
Training
The female runner’s training program must always be open to change, moving workouts around based on the menstrual cycle’s hormonal fluctuations and on how she feels. However, few female runners or coaches of female runners take the menstrual cycle into consideration when planning training, in regard to both optimizing the training and injury prevention.
They spend too much time working in their training rather than working on their training.
Working on the training means developing a system of training that is specific to female runners. It means developing a system that works. The menstrual cycle is that system. But guess what? You don’t need to create the system yourself. The menstrual cycle already exists. The system is already made for you! You only need to listen to it and follow it.
Before trying to get fancy or sophisticated with menstrual cycle-based training, the simplest (and insightful) way to implement the system is to keep track of how your athletes feel and perform during their normal training. Have them write down each day of their menstrual cycle, the data from their workouts, and how they felt during each run. After a few months of documentation, you’ll likely notice a pattern. Many female runners I have coached haven’t felt as good during workouts and experience subpar training days in the few days leading up to and including their periods. While harder workouts may be more challenging during their period, easy running may actually improve their mood and alleviate physical symptoms associated with their period. (Since estrogen begins to rise, albeit slowly, when their period starts, it’s possible your athletes may actually feel better when running during their period compared to the few days prior.)
Once you have the pattern, organize your athletes’ training around the menstrual cycle so that they run more and harder when they feel good, and less and easier when they don’t feel good. That may sound simple, but most runners and coaches like to stick to a training plan, rather than be flexible, with their plan being fluid. To squeeze the most out of your athletes’ training, your plan should be fluid, working with, rather than against, their physiology.
Through the effects of estrogen and progesterone, the menstrual cycle exerts its greatest training-related influence on aerobic endurance training. When anaerobic workouts are included in the training, the menstrual cycle isn’t so much of a consideration outside of whatever aerobic training is still being done. That’s because the menstrual cycle does not seem to affect anaerobic capacity and power (speed). Therefore, no specific times of the month are better suited for speed and power training. When it comes to strength training, however, there is some evidence that training during the follicular phase is better for increasing muscle size and strength.
Plan increases in training volume to coincide with the follicular phase (especially week 2), when estrogen is high. Refrain from increasing (or slightly reduce) weekly mileage during their period and at times of the month when estrogen is low—early and late luteal phase (early in week 3 and late in week 4). Avoid challenging workouts around your athletes’ periods, especially if they don’t feel well or if they have major cramps or feel bloated (bloating occurs from the rapid drop in progesterone as the athlete transitions from the luteal phase to the follicular phase).
Sample Training Program
This sample training program exploits the power of the menstrual cycle to plan the training, using a block and linear periodization format. The program, which assumes a four-week (28-day) menstrual cycle, begins with week 2 of the menstrual cycle, with week 1, which includes the period, as the recovery microcycle that completes each mesocycle. Thus, the mesocycles are planned in the order of weeks 2, 3, 4, and 1 of the menstrual cycle. Adjust the microcycle and mesocycle duration if your athletes’ cycles are longer or shorter than four weeks (remember, you don’t have to make each microcycle seven days).
The training load increases in a concentrated block during estrogen-dominant week 2. An extra week is added to the end of the program so the target race occurs at the end of week 2 of the menstrual cycle, when estrogen is at its peak.
Given the variability in the menstrual cycle between runners and in how female runners feel during it, I suggest you have your athletes first find their own unique pattern by keeping menstrual cycle and training logs. With a regularly-occurring menstrual cycle, they should discover a predictable pattern over a few months that you can then use to organize their specific training.
