I find as I am getting older I am much more fatigued during my period. It is like I am just a slug. During other times I can sustain a higher HR but not during my period. It also seems I dehydrate easier and have a more sensitive stomach so while most of the time nutrition is not as relevant for me it is super relevant during that week or so. I also have a lot of issues with being more prone to chafing, not a fan of chamois butter but have to use it during that time.