NYC Marathon Training - Custom Performance NYC

What is a period?


In honor of all the badass runner ladies out there, I’m taking a page out of Kathleen’s book to talk about periods! Sorry men, this blog is not directly applicable to you. However, it’s helpful to understand normal menstrual biology for the women in your life!

Kathleen has previously written blogs about losing your period (“amenorrhea”) with running, which is a symptom of Relative Energy Deficiency in Sport (RED-S). If this is something you’re dealing with, it’s time to investigate. This is not normal. If you want more information on the “why”, check out those previous blogs.

The purpose of this blog is to understand what is considered “normal” when it comes to monthly cycles and to introduce you to some hormones you may not know about. This is the first step in understanding what’s abnormal!

So what is a period? In the simplest of terms, a period, also known as menstruation, is when the body sheds its monthly buildup of the lining of your uterus. Throughout the monthly cycle, the uterus builds lining to prepare for pregnancy while the ovaries simultaneously mature follicles that contain eggs. In a normal cycle, an egg is released each month. About two weeks later, if you aren’t pregnant, your hormone levels (estrogen and progesterone are the key players here) drop to a level that tells your body to begin menstruation.

So generally speaking, if you don’t ovulate, you won’t get a period. There is also something called an anovulatory cycle where you get a period despite not ovulating, but this is usually found in women with irregular cycles.

The menstrual cycle is counted from day one of your period to the first day of your next period. A regular cycle is considered to be anywhere between 24-38 days. The words “regular” and “normal” become important when talking about cycle length. Your personal cycle may vary in length by a few days or maybe predictable up to the hour, but both scenarios are normal.

Every woman’s cycle is split into two phases: the follicular phase and the luteal phase. The follicular phase begins on day one of your cycle and goes until ovulation. During this phase your brain is producing a hormone called the “follicle-stimulating hormone” which does exactly that: it tells the ovaries to start growing an egg for ovulation. You have multiple follicles (which contain eggs) growing during this phase, accompanied by a rise in estrogen, but only one follicle will become dominant and release an egg. This phase can last anywhere from 10-22 days and is considered normal to vary from cycle to cycle.

The second phase is the luteal phase, which is from ovulation until day one of your next period. The follicle that released the egg becomes something called a corpus luteum which produces progesterone as well as estrogen. PMS symptoms are a result of progesterone peaking about halfway through this phase. The corpus luteum then breaks down about one and a half weeks after ovulation (if you aren’t pregnant) resulting in dropping estrogen and progesterone levels. This causes menstruation and begins the next follicular phase. The luteal phase is typically 14 days, but between 9-16 days is still considered normal.

If you just read this blog and thought “whoa I had zero idea about any of this” or, “I have no clue how long my cycle actually is” you aren’t alone! Unlike our male counterparts, women have hormonal fluctuations happening in our body on a regular basis. Understanding what’s happening and when can give you more insight on why you may feel super energized during some parts of the month and a little sluggish during others.

As always, we’re here to answer any questions you may have!

Menstrual cycle tool. (2018, March 16). Womenshealth.Gov. Link to the source

Skip to content