It started warming up after the first 2 hours into the race. Runners really appreciated the hoses and misting stations! "As much as 70% of the total chemical energy used during muscular contraction is released as heat rather than as athletic endeavor" (Tim Nokes, MD, Lore of Running). That is why Runner's World says to add 30 seconds/mile to your pace for every 5 degrees over 60°F. Runners slow down in the heat/humidity because your body allocates some of the oxygen previously used to fuel the muscles to the skin capillaries for cooling.