Fuelling Your Cycle

The effects of the menstrual cycle on physical performance are being increasingly recognised as a key consideration for women’s sport and flagged as a critical topic for further research. Sex hormones have influence over our metabolism and other key aspects of physiology both during exercise and at rest. It is important to consider how sex hormones may affect exercise performance, as understanding when performance may be improved or impeded by the cycle allows women to tailor their nutrition, exercise program and recovery accordingly.

Most women are somewhat familiar with the stages of the menstrual cycle, however many aren’t aware of the non-reproductive physiological effects, including metabolism, altered fluid retention, mood, sleep, sexual function and modified cardiovascular, muscular, thermoregulatory and metabolic responses.

For the many female athletes questioning the role of the menstrual cycle in their performance, data is conflicting, with no real consensus on whether exercise performance is affected by menstrual cycle phase.

A recent 2020 review in Sports Medicine examined data from 51 studies in order to find a possible reduction in performance during the early follicular phase compared to all other phases of the cycle, however the effect size was low, with no uniform recommendations established. The authors recommended that a personalised approach be taken based on an individual’s response to exercise performance across the cycle, with emphasis placed on examining and understanding the potential influence of hormonal fluctuations.

The purpose of this article is to share evidence based physiological effects that may be experienced during the cycle to equip women with the knowledge to support themselves physically and nutritionally throughout the different stages to optimise athletic performance.

Tracking Your Cycle

To understand how the menstrual cycle affects performance, it’s imperative to begin to track your cycle to understand what phase you are in. Doing so can help you become more aware of any resulting symptoms, provide guidance on how to adjust your training and teach you how your period can truly become an ergogenic aid.

Every woman’s cycle is different and many factors can play a role including the use of contraceptives, low energy availability and medical conditions including Polycystic Ovarian Syndrome (PCOS). When there is an imbalance between estrogen and progesterone, multiple parameters can be affected, including adverse symptoms of pain, fatigue, increased water retention, sleep disturbances, mood disorders and heavy menstrual bleeding, all of which will affect athletic performance.

The menstrual cycle is not just the bleed phase. If we have regular periods, then we are healthy enough to adapt to training. If a woman is not bringing in enough nutrition and doesn’t have enough recovery time, then they will start to have a depression in the endocrine system with thyroid rate going down, LH starting to drop and we start seeing menstrual cycle dysfunction such as longer cycles. When we start to see changes in the bleed or length of cycle, it is an early sign that our bodies are not adapting well and we are under too much load.

Fortunately, there are many tracking apps out there on both Apple and Android devices which make tracking a simple process. Some popular apps include:

• Flo
• Clue
• FitrWoman
• Apple Watch

The menstrual cycle is a monthly series of hormonal changes a woman’s body experiences in preparation for potential pregnancy. The cycle is counted from the first day of menstruation up until the first day of the next cycle, when bleeding begins again. A menstrual cycle lasts ~28 days, with most falling between 25-31 days.

The menstrual cycle is divided into four phases:

1. Menstruation (the bleed): Typically lasts 3-7 days, it is when a woman gets her period and estrogen and progesterone levels drop to their lowest point. Menstruation (the bleed) kicks off the follicular phase.
2. Follicular Phase: Typically lasts 12-14 days, begins day one of a woman’s period and continues until ovulation, this phase is marked by the beginning of estrogen rising. During this phase, Follical Stimulating Hormone (FSH) and Luteinising Hormone (LH) levels increase, with FSH levels higher than LH in the preovulatory phase.
3. Ovulation: The surge in LH triggers ovulation where a mature follicle ruptures releasing an egg into the uterus. This phase lasts between 24-36 hours. Progesterone and estrogen levels begin to rise.
4. Luteal phase: During this phase, the ruptured follicle becomes the corpus luteum and secretes progesterone and small amount of estrogen. The mid luteal phase contains the peak in progesterone and the second, smaller, peak in estrogen to prepare the endometrium for the implantation of a fertilised egg. The luteal phase ends in pregnancy if a fertilised egg is implanted, however if the egg remains unfertilised, the corpus luteum degrades, causing a decline in progestogen and estrogen as the cycle starts again. The uterine lining detaches, and menstruation starts again.

Follicular Phase Considerations

The follicular phase, also known as the low hormonal phase, where estrogen and progesterone levels are at their lowest. With the onset of the bleed, and the effects of lower hormone levels, the following points should be considered:

1. During the follicular phase, there may be some physical symptoms associated with menstruation, e.g. bloating, cramping, inflammation and fatigue, however, periods should never be painful or heavy and most Premenstrual syndrome (PMS) symptoms can be addressed through diet and specific supplementation such as a quality magnesium. For reference, a normal bleed is anywhere up to 80mL over the entire period. If you are experiencing discomfort or heavy bleeding, please book in for a consultation with a member of our team who can complete an assessment.
2. During this phase, aim to consume iron rich foods including red meat, chicken, fish and eggs to replete iron stores, however don’t forget that whole grains and legumes like beans, fermented tempeh/tofu, peas, chickpeas and lentils can also deliver iron. You should also get fishy! In addition, aim to consume foods high in omega-3 fatty acids to help fight increased inflammation. Think salmon, mackerel, tuna, herring and sardines, along with nuts and seeds such as chia and walnuts.
3. The way our bodies metabolise macronutrients, in particular carbohydrates and protein, changes throughout the cycle. Studies have indicated that progesterone and estrogen may alter substrate utilisation (glucose and fats), which can affect endurance performance. The nature of the follicular phase also makes the female body more insulin sensitive meaning the body can handle and access carbohydrates for fuel much more efficiently.
4. The follicular phase of the cycle may be an optimal time to focus on high-intensity and strength efforts, think PBs in the gym and sprint/hard out efforts on the track/field. This is not only due to an increased pain tolerance and anabolic/muscle-building effects of estrogen, however women have been reported to have more vigor and more confidence around ovulation. Therefore, from a training perspective we can leverage these times in the menstrual cycle where the body is saying ‘bring it on’!
5. During this phase, the immune system is geared to be more innate and primed to capturing pathogens through macrophage. If you’re going to hit it super hard and evoke that post exercise inflammatory response, your body has a better ability of understanding that as an acute response due to exercise stress and overcoming it. However, after ovulation, there is a switch in the immune system to be pro-inflammatory. This makes sense, as the body doesn’t want to be potentially attacking a fertilized egg. Therefore, there are more pro-inflammatory responses after ovulation which can dampen adaptation.
6. Estrogen receptors are present in all musculoskeletal tissues including muscle, bone, ligament and tendon. In the late follicular phase, just before ovulation occurs, females should consider that the surge in estrogen may lead to decreased stiffness of tendons and ligaments and an increased risk of both muscle and tendon injuries e.g. ACL injuries.

Luteal Phase Considerations

The luteal phase, also known as the high hormonal phase, is when the body prepares for a potential pregnancy. During this phase there are high levels of progesterone and estrogen which can affect the body in several ways:

1. Increased levels of estrogen and progesterone have been shown to suppress gluconeogenesis. Gluconeogenesis is a cellular process necessary to utilise energy stores in the body. External carbohydrate sources will therefore become more critical for sustained energy during endurance exercise, especially when the duration is longer than 60 minutes. This glycogen sparing state may also make it more challenging to reach higher intensities without appropriate fuelling. The take home message is that athletes preparing for an endurance training session or event must ensure they take in adequate carbohydrates to meet their body’s increased requirements.
2. Estrogen increases the availability of free fatty acids for fuel during cardiovascular exercise by promoting lipid oxidation in skeletal muscle. A study found carbohydrate oxidation rates were lower and fat oxidation rates were higher in the luteal phase than the follicular phase during 60 minutes of running at 65% VO2 max, meaning the body is more efficient at using fat stores for fuel during exercise. Studies have also found that greater fat oxidation in the luteal phase is magnified by a period of low carbohydrate dietary intake and the change in substrate oxidation between the luteal and follicular phase appears to be intensity-dependent. Therefore, as exercise exceeds the lactate threshold, the demand for increased carbohydrate consumption will begin to outstrip the fat oxidation influences of estrogen.
3. Progesterone promotes protein catabolism, so it is imperative to ensure adequate protein is consumed. The recovery window is a lot tighter for women, as they return to basal metabolic rates within a few hours. Look to consume at least 30g of complete protein within the hour post training and continue consuming adequate protein in intervals throughout the day to meet your personal daily requirements.
4. During the luteal phase there may be a slight decrease in anabolic, or muscle-building ability as progesterone is thought to have anti-estrogenic effects. It could therefore be speculated that the beneficial performance effects of estrogen are likely to be greater in the late follicular and ovulatory phases when estrogen is high without the interference of progesterone, compared to the mid-luteal phase when both estrogen and progesterone are high. More research in the late follicular phase is needed to validate this.
5. Fluid status changes throughout the cycle and has an impact on the ability to exercise, especially in hot and humid climates. Performance in heat and humidity can be more difficult during the luteal phase due to an elevated core temperature (of a least 0.3 degrees Celsius) and a reduction in blood plasma volume due to fluid redistribution throughout the body. This drop compromises the amount of oxygen delivered to the muscles and reduces sweat rate – since sweat helps the body cool down, it can also result in an increase in body temperature. The take away – women should be more aware of their hydration and fluid intake during the mid-luteal phase and not just drink to thirst, especially when exercising in hot and humid environments.

Reframing your cycle, the power is yours!

Taking a closer look at how the female body changes throughout the menstrual cycle is an incredibly helpful tool for females. Having knowledge of the basic physiological changes attributed to hormonal fluctuations, enables women to set themselves up as best they can to reach their health and fitness goals.

The menstrual cycle should be considered as a part of the female athlete profile so that women can maximise rewards and minimise risks to achieve their full athletic potential. This emerging field of study will play out over the coming years and decades – it’s truly exciting to see where it goes from here.

Learn More, Join the Masterclass Fuelling Your Cycle on April 26th

I’d love for you to join me for my upcoming masterclass – Fuelling Your Cycle, we will cover the stages of the menstrual cycle, what’s normal and what isn’t, nutrients and supplements to focus on and how you can fuel appropriately through different stages of the menstrual cycle to optimise performance and health. Book your ticket here.

References

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Wohlgemuth K-J, Arieta E, Brewer G-J, et al. Sex differences and considerations for female specific nutritional strategies: a narrative review. J Int Soc Sports Nutr. 2021;12(27). doi: 10.1186/s12970-021-00422-8

Meignie A, Duclos M, Carling C, et al. The Effects of Menstrual Cycle Phase on Elite Athlete Performance: A Critical and Systematic Review. Front Physiol. 2021;12. doi: 10.3389/fphys.2021.654585

Freemas J-A, Baranauskas M-N, Constantini K, et al. Exercise Performance Is Impaired during the Midluteal Phase of the Menstrual Cycle. Med Sci Sports Exerc. 2021;53(2):442-452. doi: 0.1249/MSS.0000000000002464

Jonge X-J, Thompson B, Han A. Methodological Recommendations for Menstrual Cycle Research in Sports and Exercise. Med Sci Sports Exerc. 2019;51(12):2610-2617. doi: 10.1249/MSS.0000000000002073

Sims S-T, Minson C-T, Paul B. Menstrual Cycle Hormonal Changes and Energy Substrate Metabolism in Exercising Women: A Perspective. Int J Environ Res Public Health. 2012;18(19). 10.3390/ijerph181910024

Oertlet-Prigione S. Immunology and the menstrual cycle. Autoimmunity Reviews. 2011;11(6-7). doi: 10.1016/j.autrev.2011.11.023