Mistake #1: Neglecting sodium leading up to the race.
During your taper, you’ll reduce your food intake, which consequently decreases your sodium intake. You need to replace this loss through extra 
electrolytes in a fluid. Nutrition and performance coach Krista Austin, Ph.D, suggests maintaining sodium stores in two ways in the lead up: 1) Consume electrolyte beverages throughout the day, with drinks that provide at least 200mg of sodium per 8oz and/or 2) Load up by consuming about 3,500–4,000 mg of sodium 18–24 hours before competition. The additional sodium, which should be above your normal intake, can be spread out between 2–4 meals or snacks. If you drink water, do so only at meals.
Mistake #2: Sticking to your typical warmup.
One of the worst things you can do is warm up too much before a race with high expected temperatures. “The warm temperatures will heat the muscles naturally and in a race as long as a 70.3 or Ironman, you have plenty of time to gradually bring up the pace,” Austin says. Stick to the plan of going out easy and finishing strong, and use pre-race time to keep your core temperature down—Austin suggests wrapping ice around your primary muscles.
Mistake #3: Dressing inappropriately.
We know your black tri kit is slimming and all, but lighter colors will keep you cooler longer, especially when it comes to headwear (bring the white hat to throw ice cubes in). If you’re used to wearing compression sleeves while racing, skip them in high temps. Consider arm coolers, such as the Zoot IceFil Triathlon Arm Coolers or Craft Body Control ArmCOOLers, which will reduce skin temps and provide protection from the sun. Depending on how your body typically reacts to heat, you may want to wear a normal helmet instead of an aero one. Also, although it’s a small detail, wear low-cut socks.
Tip: While preparing for the Ironman World Championship in 2005, Torbjørn Sindballe tried wearing a latex glove while running, putting ice cubes in it to stay cool. He found a reduction in heart rate, and the ice melted quicker than it did in his hat—showing that the palms emit a lot of heat.
Mistake #4: Shooting for a PR.
You can’t keep the same goals you had for your dream cloudy, 73-degree day. Get more realistic about the pace you had in mind and adjust performance goals according to the temperature. Don’t base goal race pace on miles per hour. Instead, go by power (if available), heart rate or simply perceived exertion. Forcing your body to adhere to a set pace regardless of weather conditions will make you more susceptible to dehydration and exhaustion.
Mistake #5: Trying a new fueling strategy on race day.
You’ve heard it before but we’ll repeat it again: Don’t do anything new on race day. If it’s hot, you may be tempted to grab additional fuel and fluid from aid stations that your body isn’t used to. “The body must be trained to absorb and transport carbohydrate and fluids,” Austin says. “Try to avoid taking in carbohydrate sources and extra fluid that the body is not use to processing—use what you have trained on and hopefully you have found the best solution well in advance of the race!”
Mistake #6: Overhydrating or drinking only water in the race.
Often athletes go into “must hydrate as much as possible” panic mode when it gets hot, but drinking too much (especially only plain water) is also a risk and can lead to hyponatremia, a condition resulting from too much fluid and not enough sodium in the blood. Hyponatremia can lead to, ironically, similar GI issues brought on by dehydration, such as nausea and cramping.
Sports dietitian Lauren Antonucci suggests taking in an average of 800–1000mg per hour of sodium during a race, using electrolyte beverages and/or salt tablets. Also, do an at-home sweat test in similar conditions to those you’ll be racing in. Weigh yourself nude. Work out at race pace for an hour. Empty bladder and weigh yourself nude again. If you lost two pounds (32 ounces), your sweat rate is 32 ounces per hour and you should aim to replace 60–80 percent of that.
