French swimmer Caroline Jouisse has been keeping track of her periods using her phone over the last year, collecting information for her coaches ahead of competing in the Paris Olympics this summer.
The data helps her plan the best time to work on building her muscles, which is ideally in the middle and at the end of her menstrual cycle when her testosterone levels are at their highest.
"It's important to know when my testosterone peaks are, because that is when you feel your best and will be at your strongest in training," said the 29-year-old, who will compete in the 10-kilometer open water event at the Paris Games.