But they are at risk as well when the heat index rises. Keeping ahead of their thirst is the key, not just drinking when they feel thirsty, taking breaks is essential when intensely exercising in the heat for more than one hour. This includes rest, finding shade from the sun, and drinking water mixed with sugar and electrolytes. Salty pretzels, fruit and nuts are always a good option if you don't have access to a drink with sugar and electrolytes.