Increasing environmental temperature during exercise leads to earlier quitting due to cardiac drift.

“Increasing temperature increases the rate of quitting in part, not entirely, but in part because of this thing called cardiac drift which you've probably experienced if you've been out on a hot day and you're walking uphill you might stop to take a breath.”

“Increasing temperature increases the rate of quitting, in part, not entirely, but in part because of this thing called cardiac drift. Heat increases heart rate. Effort increases heart rate. At a steady effort, you'll have a steady heart rate. If you increase the heat in the environment that you're engaging in that steady heart rate, your heart rate will now go up due to cardiac drift, and you will quit.”