Women are not small men. Some of you may be familiar with this phrase as made famous by Dr. Stacy Sims, a leading researcher on female physiology and endurance. This statement could not be more true. Though some women may train just the same as their male counterparts, the truth is our physiology differs from theirs in more ways than just our menstrual cycles. Even today in 2021, women and their periods are not as highly discussed and understood when it comes to endurance training as one would think. With so much literature produced regarding the field of physiology, comparatively, research into women’s specific physiology does not come close.
Women’s endurance sports are highly competitive and growing day by day. We want to get the best out of ourselves and in order to do this, we need to work with our physiology, not against it. The better informed you are about what is occurring prior, during, and after your period can help you understand why you feel the way you do, how to help boost your performance regardless of the time in your cycle, and ways to manage side effects.
Understanding Your Cycle
As a refresher in case you have forgotten: Your cycle averages approximately 28 days, though there are ranges between 21-35. These 28 days are broken down into two 14 day phases: the follicular and luteal phases. Days 1-14 are known as the follicular phase, while days 15-28 are known as the luteal phase. Ovulation will occur within the middle of these phases and your changing hormone levels are the catalyst for all of this.
Hormones at a Glance
The follicular and luteal phases both contain differing levels of hormones. This cascade of rising and falling hormone levels causes changes within our physiology and in turn, affects how we feel during training/racing.
- Days 5-6 your ovaries gradually ramp up the production of estrogen
- Rise in FSH (follicular stimulating hormone)
- Approximately day 12, your estrogen levels surge along with LH (luteinizing hormone)
- Due to surges: ovulation occurs
- Luteal Phase begins
- Hormones ramp-up
- Estrogen and progesterone will peak approximately 5 days prior to menstruation
- PMS kicks in!
- If the egg is not fertilized (aka your body is not preparing for pregnancy) then your period occurs and you repeat the process from day 1.
Periods and Performance
While many believe it to be better to not have race day fall during their menstrual cycle, you have no reason to fear if it does! For women, your hormones are favorable for performance once your period begins. Let’s examine a bit closer: if you are not preparing for pregnancy, then your body begins to relax. This phase of relaxation allows the body to direct all of the energy systems that were being utilized during the high hormone phases toward your desired activity. This same logic is true when it comes to the low hormone phase. When you begin your low hormone phase (first day of menstruation) this is when activity will be perceived as feeling “easier.”
This is no means for causing panic if you find yourself entering competition during a high hormone phase. You are a woman, after all, you got this! In fact, research has shown that there show no statistically significant changes in either VO2 max or lactate threshold efforts during any phase of the menstrual cycle. That being said, there is no denying that exercise can feel harder and you may find that your performance is slightly impaired. So if you feel like at least once a month your training is a bit off…there is a reason why! During the luteal phase, your heart rate will be higher overall. If you are struggling with adjustments to training, try focusing on something objective such as your power, speed, or pace.
Tip: If aiming to ace key high-intensity sessions during training, try aligning these sessions during the follicular phase.
On that same note, you can place lower-intensity/general endurance sessions during your luteal phase.
What to Expect During High Hormone Phases
Difficulties Building Muscle: Upsurges in estrogen and progesterone have large effects on muscle buildup and breakdown.
- Estrogen decreases anabolic (muscle building) growth
- Progesterone increases catabolic (muscle breakdown) processes
Therefore, this combination makes it harder for women to maintain muscle.
Metabolism Changes: Craving something sweet or salty right before your period? No surprise there! You can see a 5-10% uptick in metabolism in the days preceding your menstrual cycle (approximately 100-200 kcal.) Throughout your cycle, estrogen reduces your carb-burning ability while simultaneously increasing your fat burning and fatty acid availability. This is a good thing for endurance activities but requires extra carbohydrate consumption when it comes to high-intensity activity such as VO2 work. You will need to increase carbohydrate intake during pre-menstrual phases (when estrogen is rising).
Blood Volume: While most of us will experience the all too familiar bloating that accompanies your period, water and fluid changes do not stop there. Due to effects from estrogen and progesterone, you also experience a loss in blood volume. This reduction in blood volume will impact your cardiac output as well as blood pressure. Due to hormones, your body’s plasma volume will drop as well. Plasma volume is a reflection of the volume of fluid in our blood. Increased plasma volume is an adaptation to training that yields greater abilities in your body’s thermoregulatory responses such as sweating.
Tip: to combat fluid losses (especially if exercising in the heat) try using a preload hydration product the night before that contains higher levels of sodium.
Cramping and GI Issues: While not all female athletes experience these symptoms during menstruation, it is better to be prepared should this occur during competition. Cramping and GI issues are a result of prostaglandins, not estrogen and progesterone. Prostaglandins are chemicals responsible for the contraction as well as the shedding of the uterine lining. If your body creates more prostaglandins than you need, this is where you can run into some discomfort.
Tip: Talk to your healthcare professional about products that reverse the negative side effects of prostaglandins if you find these effects affect your sports performance.
Keep a Period Log: If you are someone who meticulously tracks workouts, then perhaps consider adding in your menstrual cycle. Take note of not only when your cycle starts, but how you feel and how your body reacts. Tracking these metrics over time can help you prepare accordingly for training/competition no matter which part of your cycle you are in.
The Training Athlete and Missed Menstrual Cycles
The understanding of the effects endurance training has on female athletes has evolved over the years. While there are large amounts of research that have been conducted regarding this topic, much of the conclusion remains the same: insufficient fueling can lead to a cascade of hormonal disruption. In a time where certain diet trends can become popularized within athletics, it is important to be mindful of replacing what you lose. This fueling includes carbohydrates, protein, and fats! If you find yourself in a situation where you are missing or skipping menstrual cycles, speak with your healthcare provider to discuss ways to help get your cycle back on track.