The late Larry Olsen was a big proponent of over-dressing for workouts whenever he could. He may have had other proprietary secrets that he took to the grave with him. However I took the overdressing tip from him in 1995 when I trained for the World Masters Cross-country Championships. The first t-shirt/shorts day of the spring, I resisted the urge to enjoy that textile freedom. Instead, I wore my Jacket and tights. I continued to dress for 10-15 degrees cooler than the day actually was until the big race (July). I race very well that year, especially in the heat.
Now, University of Oregon Human Performance Lab lends scientific support to his idea.