Just thought I'd share my experience, I haven't been running, but just started doing hot yoga again. My son is 3mths old. Even though I sweat profusely during the 90min class, there has been no negative effect on my supply and my son has been OK with my milk. Have fun running!! it's so hot outside!! I was thinking of running (i used to before I had my babies) but I think i'll wait until the cooler months. Haha, my poor dogs!! they will have to wait another few months before they get a good run!