Running in the Heat

​I’ll keep this short, much like my run this morning in 90% humidity.  We all know summer running feels harder, but ever wonder the real impact on your body and performance?    You may think you are just powering through it but that easy run may actually translate into an effort day if you don’t dial it back enough.  When we run in high heat and humidity, not only does our body temperature rise, but our bodies use more oxygen, and use glycogen stores faster and impact our ability to handle the lactate output.  Your aerobic system is working harder to keep up and your heart rate shows it.  From an optimal 50-55 degrees, about every 10 degrees of heat costs you 2-3% in performance and efficiency.  When the temps hit the 80s and above, your body has to work more than 10% harder to achieve the same performance result.  If your goal race is expected to be in hot and humid weather, by all means you should seek to train in race day conditions as much as possible.  Your body can adapt to running in heat but it takes time.  You really need a few weeks of heat training to start acclimating, even longer if you aren’t able to get 60-90 minute runs in.  Your body will start adapting right away but the more time you give it to get acclimated, the better off you’ll be on race day. 
When running in heat, start out slow.  Those first few runs should be shorter and slower so you aren’t taxing your system.  Hydrate early and often.  Even if you don’t usually drink a lot during a race, you will need more liquid when it is hot. Help your body retain fluids by using fuel that contains electrolytes, use salt tablets or try salty snacks before your run.  Experiment during your hot training runs so that you aren’t trying something new on race day.
If you aren’t training for anything, just take it easy.  Slow down, drink water and enjoy your miles.  And if you live in a four season climate, remember these days when the snow starts flying!