I am exclusively nursing my 4 month old (3rd kid I've nursed) and training for 2 marathons in the next 2 months. I have been diligent about hydration to make sure we both get what we need. It doesn't appear as though lactic acid creeps into breastmilk much- never had a baby refuse to nurse after long runs. I think hydrating is key- keep it up, you can do both!
