I like to run as well as step. I can run a 9 minute mile. I want to increase my endurance. I can only run 30-40 minutes at this point. My legs feel good. I feel tired, but it is the heat that gets to me. My face gets so red and I feel like I am going to explode. Is this purely a fitness issue? Does this happen to even fit people who run in 80-90 degree weather? I like to run between 7-8 pm. The sun is not intense but it is still hot and usually humid. I'd appreciate any physiological insight you can provide.