Science has known for a long time that the sensation of thirst is not the best indicator of how much you need to drink when training and racing [1] . Studies have also shown that losing as little as 2% of your body weight due to dehydration impairs physical and mental performance and losing 5% of your body weight by dehydration can reduce your work capacity by 30% [2] . And here we are, most of us, training in Central Texas in summer. So how do we know how much we should drink to stay hydrated in extreme heat and humidity? We need to determine our sweat rate in conditions that will mimic the warmest race temperatures that we'll face. Luckily, we don't need to see a doctor or go to a lab to find this out. Here's a simple protocol to determine your sweat rate and plan for hydration before, during and after training: Select a training session where the temperature and humidity (as well as your intensity) are like what you'll experience racing. At the conclusion of your