Nearly 10 years after winning gold in the heptathlon, at the London Olympics, the mother-of-two is launching Jennis, a menstrual-cycle mapping app.
It aims to tell users how to use their hormones to their advantage by exercising in different ways at different times of the month.
But experts say everyone experiences their menstrual cycle differently.
Dame Jessica remembers starting her period in the middle of the heptathlon at the Junior European Championships in Lithuania, in 2005.
“I was so preoccupied and worried that anyone was going to see that I started my period and that I didn’t have the right protection to sort myself out,” she said.
“I remember just running that 800m thinking I’m trying to run for a gold medal here but I’m also very aware that I’ve just started my period.
“I just rushed off the track and felt that I couldn’t absorb that amazing, gold-medal moment.
“That was something that really stuck out to me as an athlete.”
Period tracking is a tool anyone who menstruates, not just professional athletes, could benefit from, experts say. There are a number of popular apps on the market, including FitrWoman, Clue and Flo.
For most, the cycle is about 28 days, with four phases, during which the two main sex hormones, oestrogen and progesterone, ebb and flow, producing varying levels of energy:
The period phase: On the first day of a period, oestrogen and progesterone levels are at their lowest but begin a gradual rise – those with abdominal cramps are recommended stretching and yoga
The follicular phase: In the week after a period ends, oestrogen levels begin rising quickly in preparation for ovulation – those feeling energised are encouraged to train and push their fitness
The luteal phase: Around the time of ovulation, about 14 days before the next period for most, oestrogen levels peak – muscle building is recommended to increase endurance, with fat-burning exercise such as running, cycling and swimming
The pre-menstrual phase: In the week before the next period, oestrogen and progesterone levels are falling and symptoms include mood swings, fatigue and bloating – those with anxiety are recommended a low-intensity workout, those feeling frustration something more high impact
The US women’s football team head coach Dawn Scott said tailoring their diets and exercise around their periods helped optimise performance.
But for some, something about periods still feels taboo.
“I always remember it being an awkward conversation,” Dame Jessica said.
“I had a male coach and it was predominantly a male environment.
“I remember having those small conversations of, ‘I’m on my period, or I’m bit tired, or I’m not feeling 100%,’ but never feeling fully confident about having an open conversation about how I felt and how it was making me feel when I trained.
“That was just something that was still very much a taboo and something that we didn’t really focus on unless it was having a negative impact on my training.”
Sarah Taylor, 45, who has been using the Jennis app for months, after coming into the perimenopause, said: “Given my age, I wanted to see how things were working with my body.
“I noticed how little information there is out there about women’s health.
“It still seems to be a taboo to talk about periods – and especially the perimenopause.
“The dialogue is beginning to change though – and I want to be part of that.”
The more data users feed the app, the Jennis team says, the more bespoke the algorithm becomes – and it will work for those on irregular cycles.
“It’s definitely in its early stages – but we want to reach as many women as possible and help them understand their bodies and hormones,” Dame Jessica said.