Here’s more information regarding coffee before a run. We know it is NOT a diuretic and actually has some “pre-run” benefits.
Nothing gets me functioning in the morning better than strong coffee. And if I’m going to start my day with a dreaded workout, that steaming cup of caffeine is the exact motivation I need to get going. Although coffee might not seem like the best beverage to drink before hitting the gym, it actually has a few hidden benefits over water that may surprise you.
Source: Why You Should Be Drinking Coffee Instead of Water Before a Workout « Mind Hacks