CHICAGO (CBS) — Chinese swimmer Fu Yuanhui surprised the world in Rio last week when she spoke candidly about how getting her period had negatively impacted her Olympic performance during the 4X100 meter relay.

When asked about “stomach pain,” she said, “yes, I’m having my period.”

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lynn-rogersHow does menstruation affect female athletes? We asked Lynn Rogers, Ph.D., the director of the Neuralplasticity Laboratory at the Rehabilitation Institute of Chicago. Rogers is also an assistant professor at Northwestern University’s Feinberg School of Medicine.

CBS 2: How can one’s period potentially affect female athletic performance?

Dr. Rogers: Fu answered the question of whether she was experiencing stomach pain with the truthful response that her period had started the night before. She was very clear that she did not feel this was an excuse for what she considered to be “not swimming very well.” Yet, in mentioning her period at all, a worldwide conversation has been triggered.

Hormones impact how people function. All people. Debates regarding hormones and athletic performance extend across a number of topics at this Olympics, from anabolic steroid use, to intersex athletes, to a female athlete on her period. And the massive take-home message is that there is not yet nearly enough information available to give clear answers.

Women are unique in that their hormones fluctuate cyclically. The levels of the female sex hormones vary from day to day across the month and can impact a variety of systems that influence performance. Everything from energy metabolism, to heat management, to neuromuscular control are influenced by sex hormones.

CBS 2: What are the possible implications of women competing with their periods? What about other points during their cycle?

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Dr. Rogers: Women’s hormone levels are at their lowest during their periods. They remain low until about halfway through the month, and then — with different timings — both estrogen and progesterone levels rise and remain high. What we are coming to understand is that different hormones impact different systems in different ways, and depending on the specific demands of a sport, performance may be uniquely affected.

As an example, we know that women are approximately nine times more likely to experience ACL (anterior cruciate ligament in the knee) injuries than men, and those injuries occur disproportionately during the first half of the cycle when hormone levels are low.

What is unclear is exactly why. Research into how hormones directly impact the laxity of a joint and its ligaments has not fully accounted for these injuries, leaving open the possibility that other systems — from the brain all the way down to the muscle — are specifically influenced by hormone levels in a way that impacts how well the joint is protected from injury.

CBS 2: Will Fu’s coming forward about her period have a positive impact on other female athletes?

Dr. Rogers: I think it’s important to recognize that she simply stated a fact that is true for fully one half of the earth’s population on any given day. That we refer to this as “coming forward” may speak to why there exists an unprecedented dearth of specific, scientific information regarding how fluctuating sex hormones may impact everything from performance, to injury, to rehabilitation.

CBS 2: Do you worry that this feeds into negative stereotypes about what women can and can’t do when they have their periods?

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Dr. Rogers: There’s more to be discussed than societal taboos regarding a woman’s period. Menses is a very small piece of a repeating monthly cycle, each phase of which has its own specific characteristics. A woman’s distinct physiology has its own requirements, and the more we discuss — and investigate — that basic fact, the more we will move understanding forward to benefit all women.