Hydration for Race Day Heat: What You Need to Know Before Chattanooga 70.3
Running the Walnut Street Bridge — Ironman 70.3 Chattanooga, 2021
Race day is May 17th. If history holds, you'll be running through downtown Chattanooga in temps pushing the upper 70s to low 80s with humidity around 75%. That's not a sufferfest by July standards, but it's enough to tank your run if your hydration plan was built for a cooler day.
Here's what actually matters.
The day before
Sip your hydration mix of choice all day. Not plain water, your actual mix. Target 4 to 5 liters throughout the day, spread out steadily rather than front-loaded.
Food the day before matters too:
Breakfast: big, carb-heavy, with protein. Skip the fatty breakfast meats.
Lunch: normal but lean into the carbs.
Dinner: keep it simple. Protein and carbs. Think chicken and sweet potatoes. Nothing fancy, nothing that's going to sit heavy.
Race morning
Wake up 2.5 to 3 hours before your wave. Eat something familiar. Continue sipping your hydration mix. Don't try to catch up on fluids in the last 30 minutes before the swim. By then it's too late to help and may just make you uncomfortable in the water.
Sodium is the thing most people underestimate
You can drink every aid station and still fall apart on the run if you're not replacing sodium. Sweat contains significant sodium, and the more you sweat, the faster you deplete it. Most people think dehydration looks like thirst and dry mouth. But low sodium can also just feel like your legs hit a wall, or show up as headache, bloating, nausea, and mental fog. Drinking more plain water without electrolytes makes it worse.
On a hot day for a 70.3, you're looking at 4 to 6+ hours of racing. Individual sweat rates vary a lot, but sodium needs are higher than most people plan for. I personally aim for around 1,800mg per hour. If you're a heavy or salty sweater (white residue on your kit, eyes that sting), you likely need more than the conservative estimates you'll see on most gel packaging.
Bike leg is your best hydration window
You're not bobbing in a river or running. Use it. Start drinking within the first 15 to 20 minutes, before you feel thirsty. Carry at least two bottles and plan to use them. Front-load your fluid and electrolyte intake so you're starting the run in a good place rather than a deficit.
The Chattanooga run: two loops, full sun
The run along the Riverwalk and through downtown is exposed. Two loops means you'll know exactly how you feel at the halfway point and there's nowhere to hide from the heat. Use the aid stations. Grab ice and use it: under your hat, down the back of your shirt or bra. It makes a real difference when the sun is out.
If you feel foggy, crampy, or like your legs just stopped working mid-run, reach for sodium first, not just water.
Skip the alcohol race week
Not just the night before. The whole week. Alcohol is a diuretic and it disrupts sleep, both of which work against you when you're trying to show up ready.
You've put in the training. Your hydration plan deserves the same attention as your brick workouts. If you want to talk through what this looks like for your specific body, sweat rate, or race nutrition setup, I'm Kristin Evans, FNP-C. I work with endurance athletes through Groundwork Health and I'm happy to connect.
Good luck on the 17th.
