Anecdotal evidence shows that some people can feel fatigued when on their period, however scientific evidence shows that during exercise there’s no effect on performance or effort level during the early follicular phase of the menstrual cycle (day 1-7).
For some athletes who suffer badly from menstrual cramps/heavy bleeding they may want to plan racing around their cycle, however exercise is great for easing menstrual tension, can elevate your mood and make you feel better. If need be, take medication to deal with any pain but make sure these aren’t taken on an empty stomach.
For shorter races you may not need to change your tampon, however on longer races, i.e. half/full Ironman, have some available either in transition or in your bike saddle bag just in case you come unstuck. Some athletes use a menstrual cup, this collects blood rather than absorbs it like a tampon, and doesn’t need to be changed as often. Make sure you try this out before race day, though.
During the luteal phase of the menstrual cycle (days 19-25), when exercising in hot conditions (32oC and above) heart rate and effort level can be higher during exercise (review in Jonge, 2003), so if it’s feeling harder than usual during your race then your hormones may be to blame.
Dr Joanne Mallinson is a British Triathlon level 3 coach with Her Spirit a personalised coaching app for your Mind, Body and Fuel. Her day job is a research scientist in human metabolic physiology at the University of Nottingham which allows her to use current scientific approaches within her coaching.