Image copyright Getty Images

In July 2019, the US women's football team won the World Cup. Their success was, in part, attributed to having tracked each player's menstrual cycle and adapted individual training loads and diet accordingly.

It is an approach which many think is long overdue.

In recent years, a number of top sportswomen have talked about the impact of their menstrual cycle on their training and performance.

British tennis player, Heather Watson attributed her first round loss at the 2015 Australian Open to period symptoms, including dizziness and nausea, while British Olympic athlete Eilish McColgan believes her period contributed to a hamstring injury last year.

Research from 2016 shows that more than half of elite female athletes say that hormonal fluctuations during their menstrual cycle hampered their training and performances.

Image copyright Reuters Image caption Heather Watson says period symptoms were the reasons for her early exit from the 2015 Australian Open

Yet many women - whether elite or recreational athletes - are loath to talk about their periods to their coaches and performance teams due to embarrassment.

Now there are apps for that.

FitBit launched a "female health tracking" feature last year, enabling users to log their periods and record their symptoms.

"By having all your health and fitness information in one place and looking at your cycle trends and data over time, you can better understand the connections between your activity, sleep and cycle symptoms," says Jennifer Mellor, engineering manager at Fitbit.

"When it comes to working out, everybody is different. Energy levels may vary at different points in a woman's cycle, or they might feel strong all month long. By using the female health tracking feature, users can see clear, personalised signals to either slow down or ramp things up."

Image copyright CLue

The female health app Clue also enables users to track exercise and energy levels throughout their cycle.

"By consistently inputting this data into the app, users can gain a better understanding of how their training can differ at various points in the cycle, and adjust accordingly," says Clue boss Ida Tin.

"For example, they might find that some days are better for strength training as energy levels are higher, whereas on others, energy is lower than usual, so stretching and light exercise might be better options."

One app takes this a step further by using insights from elite athletes and making them available to others. FitrWoman is owned by sport technology company Orreco, and was co-founded by elite runner and research scientist Dr Georgie Bruinvels and product development manager Grainne Conefrey.

The training app enables users to track their periods, report symptoms, log training activity, and access nutrition and physiology support during each phase of their cycle.

The app is used by a number of top sportswomen, and Dr Bruinvels has worked with numerous elite females including USA Soccer, USA swimming and a number of Red Bull athletes.

Users enter the details of their last cycle and its duration, allowing the app to provide personalised training and nutritional suggestions, explaining the changes in the body at that time.

Image copyright Fitr Woman Image caption FitrWoman uses insights from elite athletes and makes them available to others

"The menstrual cycle has long been viewed as a barrier to training and performance," says Dr Richard Burden, physiology technical lead at the English Institute of Sport (EIS), which is currently running a SmartHER campaign aimed at promoting awareness of female athlete health.

"But if you flip it on its head, there is real potential to utilise hormone fluctuations to be more specific and precise about the training you do rather than just not training."

Monthly female hormone fluctuations can affect a whole range of physiological and psychological functions, from the way women move and adapt to training to the way they think and feel. So understanding when these phases will occur in individuals allows coaches to optimise training.

Jamie Main, head coach at Derbyshire-based Derventio Excel Performance Swim Squad, began using Orreco's coaching app five months ago. This shares athletes' profiles (with their permission) so he can monitor their status in real-time and plan ahead.

"Straight away, it normalised the conversations between myself and the athletes," says Mr Main. "It broke the false taboo on the subject.

"We could be proactive in adapting high intensity sessions when it didn't fit their cycle. There's also points in a cycle where there's higher chances of injury - increased awareness of this allowed us to build in more recovery work and progressive warm ups."

Image copyright Jamie Main Image caption Mia Slevin (l) and coach Jamie Main say the app they use has helped improve training efficiency

On the flip side, the app shows Mr Main at which points during an athlete's cycle training intensity can be increased with "back to back tough sessions", an approach which has some scientific backing.

British swimmer Mia Slevin (European junior medallist and four-time British champion) says that the app "tells me which foods are important to eat at certain times, without tracking my cycle I wouldn't know this".

For example, at times in the cycle when a users' blood sugar level may be more unstable, the FitrWoman app will advise including protein at each meal and choosing snacks with complex carbohydrates.

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British middle and long distance runner Emelia Górecka says the app has helped log her symptoms - including heavy menstrual bleeding - and adapt her training regime.

Image copyright Getty Images Image caption Emelia Górecka says she's now able to work out when she is prone to disrupted sleep patterns

"After a few months I began to notice patterns and could relate my symptoms to different aspects of training. The app would then supply tips and information around the four phases of my cycle.

"For example, disrupted sleep in phase four of my cycle is very prominent for me, so this is something I try to keep on top of - particularly in hard training blocks and around races." This includes eating foods that are rich in melatonin before bed, such as bananas.

While more research and data is still needed, the impact of such technology on women who exercise and compete at any level could be marked - and it could prove transformative for professionals.

"Technology is going to play a huge role," says Dr Burden, "in enabling us to tailor training to each individual and to find the 0.5-1% difference in performance that may make a difference between winning a gold medal and not."