Yes, the heat, I rode this morning at 9:00 AM and I just lasted 20 minutes at a walk, no trotting. It was getting to be too much for me! I could have ridden the full half-hour without too many problems, but the mare was muttering beneath her breath about my insanity of riding when it is so hot!
I LOVE my long sleeve technical fabric shirt (FITS, white). I LOVE my Kerrits IceFil silicon full seat tights. I LOVE my Moxie ventilated half-chaps. I love my ventilated helmet (Ovation, white.) Beside the technical fabrics, when I feel a breeze I stop for a minute and I drink plenty of water. There is NO SHADE where I ride so my sunglasses help a lot too.
Years ago I tried an ice-vest, it was heavy and while it cooled my torso the rest of my body got HOT. I also found the ice vest to be heavy and tiring to wear. I tried the evaporation cooling vests, but they did not work AT ALL in the high humidity and I ended up hotter when I wore the vest and the evaporative “cooling cap” (as in my skin was HOTTER when I wore the evaporative vest and cap when I took them off.)
The technical fabric shirts and tights work better for me in the high heat and humidity, and with the long sleeves the sun does not heat up my skin. When I use the technical fabric shirt, tights, and the ventilated half chaps I feel cooler that when I wore my ice vest. When I ride in the direct sun I think the sunlight helps evaporate my sweat from the technical fabrics.
The modern technical fabrics made for the heat have helped me the most when I ride in the high heat and humidity.
I just wish that the technical fabric people made a human scalp covering, human face mask and neck covering combination that would help with the sweat on my head, face and neck. That would help me SO MUCH in this brutal heat and humidity!