If you train for endurance in Dallas, you already know the summer is not something you can outrun. Temperatures regularly push past 100 degrees and the humidity makes it feel worse than the thermometer says. For runners, cyclists, and anyone logging serious miles outdoors, understanding how the heat affects your body is the first step toward training smarter instead of just suffering through it.

The most immediate impact is on your heart rate. In hot and humid conditions, your cardiovascular system has to work harder to cool you down, which means your heart rate climbs faster and peaks higher than it would at the same level of effort in cooler weather. A pace that felt comfortable in March can feel like a tempo effort in July. This is not a fitness problem. It has to do with physiology, and it’s important to understand the difference.

Humidity compounds everything. When the air is saturated with moisture, sweat evaporates slower, which is your body’s primary cooling mechanism. Dallas summers regularly combine high temperatures with humidity levels that make effective cooling difficult, especially during morning hours when dew points are at their highest. Even early starts don’t fully escape it.

During extended efforts in the heat, you lose electrolytes through sweat, primarily sodium, and replacing fluid without replacing electrolytes can leave you feeling flat or, in serious cases, create a dangerous imbalance. A sports drink, electrolyte tablet, or salted food source during workouts lasting longer than an hour makes a real difference.

Training by pace in Dallas summers is a setup for overtraining. Heart rate is a more honest metric. If your goal pace requires more effort than your body can sustain safely, running by effort or heart rate zone instead of hitting a specific split protects your fitness and keeps you healthy into the fall racing season.

Shorter intervals, earlier start times, and more recovery between hard sessions are not signs of weakness. They are the adjustments that let you come out of summer in better shape than when you went in.

Dallas summers are long and unforgiving. The athletes who handle them best are the ones who stop trying to train around the heat and start training with it in mind.