Women’s Cycles and Triathlon: the Real Effects on Training and Racing

The author and CBCG athlete Amy VanTassel chilling in The Dead Sea

The author and CBCG athlete Amy VanTassel chilling in The Dead Sea

by CBCG Coach and Co-Founder Molly Balfe

Several years ago, a fellow coach referred a female athlete to me for help with what he called “women’s issues.” In my experience, as it relates to triathlon, this term typically applies to one of the following: whether you are supposed to wear underwear under your tri shorts, or how to train and race throughout your menstrual cycle. This athlete fell into the latter category; after spending the better part of a year training for her first Ironman, she realized that she would almost certainly get her period on race day.

CBCG Athletes Becky Matro and Cher Vasquez at our yearly Tucson Training Camp

CBCG Athletes Becky Matro and Cher Vasquez at our yearly Tucson Training Camp

Her understandable concern was exacerbated by a lack of reliable information, not to mention the nuances of approaching her male coach about the issue. Within the last century, a lack of understanding about female anatomy combined with outdated ideas about gender roles gave rise to the absurd belief that a woman should not participate in sports lest she rattle her uterus loose. It was this type of thinking that contributed to the ban on women’s ski jumping, which persisted until the 2014 Olympics in Sochi!

This history of misinformation has also contributed to a lack of evidence-based research about the specific needs that female endurance athletes have regarding nutrition, training, and racing. A recent article on USAT’s website about “Fueling the Female Athlete,” cites that “when all 2015 publications from the three leading sports science journals were analyzed, women made up only 3 percent of the 254,813 participants in 188 studies.” The unsurprising result of limiting women’s representation in sports science research is that traditional recommendations for endurance athletes are often appropriate only for men.

The good news is we are starting to see some progress. In the past few years, more resources have become available to help equip women with the tools they need to work with their physiology. Stacy Sims’ book Roar provides a tremendous amount of information for women on how hormones impact performance throughout their lifetime. The book clearly states that “women are not small men,” and therefore should not assume that fueling and training based on recommendations that were developed for men will work equally well for them.


The book also details how hormonal changes throughout the menstrual cycle can impact training. Surprisingly, the athlete who came to me because she was worried about racing while she had her period had little to worry about regarding her performance. The biggest hormonal challenges for female athletes present themselves during the high hormone luteal phase of their cycles, when blood sugar levels, breathing rates, heat tolerance, and mental focus can all be impacted. Once the low hormone phase starts on the first day of their period, performance potential and pain tolerance tend to increase.

Research about women’s specific training needs is still being done, but here are a few key points to think about when developing a plan that works for you:


For long-term training and racing, it seems pretty clear that most women will not thrive on low carbohydrate diets. As Sims’ book says, “Low-carbohydrate diets increase fatty acid oxidation during exercise and encourage intramuscular fat storage. The body is smart; if there isn’t enough primary fuel to support the stress it’s under, it’ll go for a secondary source—in this case fat—then store more of it for the next time it encounters that stress. But this does not translate into improved performance.” Female athletes are also at risk of undershooting their protein needs, especially in the post-workout recovery window. We urge all of our athletes to consume protein in the post-workout window, but for women this is extra-important: the window is shorter than for their male counterparts.



No doubt your coach has told you that recovery is a critical part of training. Strength and speed gains happen when we work and then rest, so a good training plan should include periods of lower intensity to allow you to repair the damage done to your body during periods of heavy training. Moreover, women’s ability to access stored carbohydrates is typically lower than men’s, and lower still when our estrogen levels are high, so you and your coach should develop a recovery routine that allows you to reap the gains of all your hard work. 


Postmenopausal athletes may find that they need to adjust their nutrition plans for optimal performance. Increases in insulin resistance during this time may require a move away from traditional high-carb endurance products to regulate blood sugar and prevent GI distress. Postmenopausal women should also consider adding more high intensity training (along with commensurate recovery!) to their training regimen to support muscle strength and to fight muscle atrophy/loss. 


The author on deck at a recent training camp, image courtesy of Dylan Haskin

The author on deck at a recent training camp, image courtesy of Dylan Haskin

Even with recent additions to the body of research on how women respond to training, there is much work to be done. I found a lot of the information in Roar to be extremely valuable for determining possible solutions to common issues that female endurance athletes face. I also thought it was somewhat limited in its discussion of how athletes respond to the hormones used in contraceptives and hormone therapies. My recommendation to all of my athletes is to evaluate your sources of information and find what works for you.

Our sport requires balance, and finding that balance means being clear about your goals and your needs. So tell your coach about your period! In fact, all CBCG Coaches condone tracking your cycle in Training Peaks, so if your coach is male and demurs at “women’s issues,” show him this blog post.