Co-authored by Brenna M. Lynn, PhD Candidate, MSc., CSCS
The great physiologist Olaf Astrand once wrote, “Women should not swim during menstruation because of the possibility of infection.” Although our schools of thought have evolved past this unqualified assumption, the female menstrual cycle is still a mysterious topic for most athletes and coaches. Over the past number of decades, women have made dramatic gains in athletics, both with the increase in overall participation and the elevation of performance standards. There has also been an increase in scientific research involving studies focusing on women’s health and sport performance issues. Throughout puberty to menopause, it is the fluctuating levels of endogenous hormones that impact a number of physiological variables. The question is whether or not these hormones directly affect a female athlete’s sport performance. In the land of fact and fiction, this article answers the questions of: Can I compete when I am menstruating? How do hormone levels fluctuate and change over the cycle? Do hormone levels affect muscle strength and fatigability? How do hormone changes affect prolonged endurance activity?
The menstrual cycle is the result of an intricate system of feedback that involves the hypothalamus, anterior pituitary and the ovaries. Hormones released by the pituitary include follicle stimulating hormone (FSH) and luteinizing hormone (LH). These hormones regulate activity of the ovaries. Estrogen and progesterone, hormones from the ovaries, regulate changes within the uterus in preparation of a fertilized egg. Each month, an egg (ovum) is released from an ovary where it migrates to the fallopian tube. The follicle it leaves behind grows into a small endocrine gland, called a corpus luteum. This stimulates the hormone progesterone to line the uterus with blood in preparation for possible fertilization of the egg. If this does not occur, the uterus sheds its lining. This is termed menstruation. Two weeks later, the same cycle begins again.
A typical menstrual cycle lasts about 28 days but may range from 20 to 45 days in healthy women. The phases of the menstrual cycle are characterized by changing levels of the two primary hormones: estrogen and progesterone. The follicular phase starts with menstruation and ends with ovulation. In this phase, levels of estrogen and progesterone are relatively low. In a typical 28 day cycle, ovulation occurs around day 14 (with day one being characterized as the first day of menstruation). Just prior to ovulation, there is a dramatic rise of estrogen in the absence of progesterone. Around this time, there is also a surge of LH. It stimulates the production of androgen from the ovary and increased FSH that promotes the growth of the follicle and the production of estrogen. Ovulation is the result of the sudden surge of LH and produces the corpus luteum as mentioned earlier. The luteal phase is the last phase of the menstrual cycle that occurs from ovulation to the onset of menses and is characterized by increased levels of estrogen and progesterone. During the luteal phase, there is a point-three to point-five degree Celcius increase in basal body temperature.
This information is based on an average 28 day cycle.
* Note: The gold standard for determination of menstrual is hormonal verification with blood samples. Ovulation prediction kits detect LH through an ELISA assay in the urine, but LH surge does not always precede ovulation. De Souza et al found about 10 to 55 percent of women did not show ovulation after the peak LH surge. Well conducted research must qualify this by using an ovulation prediction kit.
The important aspects of exercise physiology to consider are if and how women are affected by the hormones that regulate the menstrual cycle. In the literature, scientists have examined the subject’s response to exercise stress during different phases of the menstrual cycle. Examinations have shown that the fluctuating endogenous hormones estrogen and progesterone are known to possibly affect cardiovascular, respiratory, thermoregulatory and metabolic parameters. Past research literature has utilized maximal as well as sub-maximal oxygen consumption protocols, lasting anywhere from 15 to 90 minutes. Some research has also been done using anaerobic testing protocols. Subjects of all ages, training backgrounds and fitness levels have been measured.
Aerobic performance, as measured by maximal oxygen uptake, was not altered between menstrual phase during a normal ovulatory menstrual cycle. However, a slight decrease in VO2max was shown during the mid-luteal phase of the menstrual cycle in 16 elite athletes. The mid-luteal phase tends to show more respiratory strain as studies have shown increased minute ventilation and greater subjective breathlessness that is thought to be caused by elevated progesterone levels present during this phase of the menstrual cycle. Conversely, Jurkowski et al found that exhaustive exercise (i.e., time to exhaustion at a workload of 90 percent of maximum) was prolonged or rather improved in performance during the luteal phase of the cycle.
Masterson found power performance in a Wingate cycle test was higher in the luteal phase, whereas another study by Miskec et al concluded that repeated maximal intensity exercise was not affected by any phase of the menstrual cycle.
A well-designed study performed by Lebrun, where the phase was confirmed with documentation of ovulation, measured the anaerobic power of active females during the Cunningham and Faulkner Anaerobic Speed Test. It found there was no influence on performance with each phase of the menstrual cycle. Other studies have also found that the menstrual cycle does not affect blood lactate concentration in response to exercise. Literature and research by Giacomoni focused on alactic and lactic power included a multi-jump test, a squatting jump test and a force-velocity test on a cycle ergometer. It concluded that there was also no influence on the phase of the cycle but did add that those subjects with premenstrual and menstrual symptoms (i.e., lower back pain, cramping, headache, anxiety, loneliness, anxiety, etc) did have significantly lower maximal cycling power.
The current literature suggests that the fluctuations in female hormones throughout the menstrual cycle may not affect muscle strength and fatigability. A unanimous finding of all of these different studies suggest that regularly menstruating female athletes competing in either strength/power sports or intense anaerobic or aerobic sports do not need to adjust their competition schedule for menstrual cycle phase to maximize their performance.
However, just like most rules, there seems to always be one exception: Prolonged, aerobic exercise in the heat. In this case or scenario, the menstrual cycle may have an affect on an athlete’s performance. During prolonged exposure to hot conditions, there is scientific evidence of a decrease in exercise time to exhaustion shown during the mid-luteal phase (days 15-22) when the body temperature is elevated. This was mentioned earlier with respect to respiratory strain and increased core body temperature. This small elevation in core body temperature increases the heart rate and can place an abnormal strain on the cardiovascular system. Therefore, there should then be an adjustment of the competition schedule in hot, humid conditions when the athlete is working above 65 percent of their VO2 max during days 15 through 22 of the menstrual cycle.
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