I from time to time get on my own case for being a bit not-so-fit in a cardiovascular type fashion despite the fact that I exercise regularly and also kind of watch what I eat. It is always nice to discover that my shortcomings are not necessarily because of anything that I am doing wrong but instead, where I live and perhaps what kind of person I am.
Right now I am in the Dominican Republic, and in case you didn't know, this is a hot country (never has any winters) and I spend most of my life living in Thailand, a hot country also. When I run / jog in Thailand outdoors, I can rarely accomplish very much. Normally I can only get a few kilometers in before I am dead on my feet, about to collapse from heat exhaustion, breathing extremely hard, and feel like I will be dead soon.
Today, in the Dominican Republic, I easily ran nearly 8 km on the beach with no shoes on, in the sun with zero problems. I could have run further but again, I ran out of beach. The reason for this is not something I investigated in any sort of scientific sense but I can sense these things, and it boils (pun intended) down to this: It is far less humid here than in Thailand.
It seems as though I am negatively affected by humidity as far as my exercise regimen is concerned. Basically, I am simply not cut out for it. To be honest with you I can't really understand who would be since I easily sweat through all I am wearing in just a few km in Thailand and today, on the beach, in the sun, at mid-day in the Dominican Republic, i felt like I could have kept going for a loooooong time.
I have never had to think about this because I have never been trying to exercise in multiple climates in a short span of time. In a shell (and someone with more knowledge, please feel free to expand on this,) the sweat on your body must have a chance to evaporate in order for you to ever cool down. When the humidity is super-high (like it is pretty much all the time in Southern Thailand) you will never reach that point because the air is so heavy and hot anyway - therefore you never cool down and are just uncomfortably hot and wet.
Sorry if it took to long for me to get to the point and even sorrier if this is boring. Basically, I am just really happy that I am not in horrible cardiovascular shape and that there were other factors at play. If you live somewhere super-humid, you might be in the same boat as I am.