6 Tips to Effectively Train at Intensity in the Heat

The US (and a good part of the rest of the world) has been experiencing a serious heat wave. In fact, one of the storylines of the ongoing Paris Olympic Games has been the high temperatures. And just like Olympians, for most endurance athletes (and those just looking to stay in shape), hard training and exercise doesn’t stop for hot weather. 

Over the years, I’ve posted about how to exercise, train, and race in the heat on a few occasions. We all know the dangers of dehydration, heat exhaustion, and even heat stroke that are associated with strenuous exercise in hot conditions, yet even the most experienced among us can still get things wrong. At best, we end up with a poor training session, and at worst we can end up with a trip to the ER. 

Most of us have done the “low and slow” pure aerobic efforts in hot temperatures- whether that be in a race, or just a training run or ride. But what about when we have to do threshold work, or Vo2 max repeats, or hill sprints? Do we just forget about those hard training sessions during 4 months of insufferable heat?  Herein lies the conundrum: How in the world can we SAFELY execute high-intensity workouts in hot, humid conditions? 

Let’s dive in:

Before we address how to handle a high-quality (high intensity) workout in the heat, it’s helpful to understand what happens to the body when it gets too hot while exercising. In short, we can overheat which leads to heat exhaustion. I took a bit of the following from an article on Johns Hopkins website about heat exhaustion: 

“Exercise-related heat exhaustion is an illness caused by getting too hot when you exercise. During heat exhaustion, your body temperature rises above normal.Your brain usually keeps your body temperature within a degree or two of 98.6°F (37°C). This temperature control is important because many processes in your body only work well within a certain range of temperatures.”​

The body can regulate temperature a few different ways: 1)  The body can cool itself by sweating. When sweat evaporates, it lowers core temperature. (This is why humidity can be such a challenge to adapt to, as when humidity levels are high, the moisture in the air negates the evaporative effects of sweating) 2) The body lowers its  temperature by sending more blood to your skin and to your arms, legs, and head. This lets more heat escape. However, during hard efforts, blood is already sent to the legs (and arms) to generate movement, which diminishes its cooling effects.  If the body cannot get rid of the extra heat, the body temperature will rise, along with the heart rate and perceived effort, even if the effort stays uniform. 

So in essence, we struggle when the effort is high and it’s warm and humid outside. However, we can’t just drop all of our high intensity workouts just because it’s July in Virginia. Of course, we know of the importance of staying hydrated, maintaining an adequate electrolyte balance, and training while properly fueled - and their importance cannot be understated while training in the heat- but there are a few other levers we can pull to help us specifically during hard efforts outside. By manipulating a few important variables, we can optimize our high-intensity training sessions (aka- keep that effort high throughout the workout and maximize it’s benefit) AND safely navigate the heat by allowing the core temperature and HR to remain as low as possible:

1) We can adjust the duration or frequency of our high intensity intervals. An ‘intensity-based ’ interval workout can take many forms, from High Intensity Interval Training (HIIT) strength sessions in the gym,  to mile repeats on the track, to hill sprints on the bike, and any number of other efforts. When we do these in the heat, however, the effort required to do them increases as our body continues to heat up. So, one way we can still maintain the quality of the session and the integrity of the workout is to simply shorten the TIME  of the effort OR the overall number of efforts. This way, our body still gets the stimulus of the hard effort, but we can prolong our body’s rise in core temperature  due to the shorter time period of the effort. 

2) Adjust the recovery interval. Another way to keep the core temp and HR lower longer is by increasing the time in between efforts. The RI (or ‘Recovery Interval) is the easy effort in between the hard intervals. For example, if we are doing mile repeats at our lactate threshold on the track and the recovery interval is 2 min walking/easy jogging, then maybe we extend that to 4 minutes, allowing the HR to recover a bit more before the subsequent harder effort. 

3) Run/ride/swim by feel instead of pace. As a coach, I give athletes pace and power ranges to help govern their high-intensity efforts. However, after several of these types of workouts, most experienced athletes are pretty good at running, riding, or swimming in a particular pace range based on feel. Now that doesn’t mean we all can nail a pace on the track within a few 100th’s of a second- what I’m referring to is that we know what it FEELS like when we’re running at our approximate threshold pace, or cycling near our Vo2 max. So, in the heat, train by feel instead of focusing on your watch. On a track it could be 15-30 seconds slower per mile running in 85 degrees instead of 55 degrees. 

4) Go indoors…sometimes. Optimizing high-intensity workouts should be the goal of every session, and that may necessitate the need to go indoors. In fact, many times is preferable. Indoors, we can control all aspects of the session - temperature, humidity, access to hydration and nutrition, etc. However there are drawbacks. We are unable to hone our bike handling skills, practice downhill running at speed, or perfecting our open water skills. So, many times in hot conditions, a hybrid approach can be the best of both worlds. When performing high intensity running intervals in the heat, many times I do my warm up-easy running . Then, mid run I go indoors and do the hard intervals in my climate controlled studio on the treadmill, finishing up any remaining low intensity running outdoors at the finish. A hybrid or even pure indoor approach is a great way to preserve the integrity of the session without overheating. 

5) Be flexible when you train (if possible). We know that the coolest time of the day is usually between 6-7 am. Early morning and late evening offer more shade from direct sun early. Also, if you live in a humid environment, the humidity levels are typically higher in the morning and lower later in the day, which can affect the heat index. So by paying attention to these factors, and moving your workout times accordingly, can significantly affect the quality of your higher intensity workouts. Obviously, some may not be able to alter the times they train, but if you can, you’ll see a big difference between running track intervals at 6 am in full shade and 68 degrees before work versus, 6 pm in full sun and 88 degrees. 

6) Above all else…know when to quit. We all need to understand our limitations, and our physiology. When training in the heat and our interval times are becoming increasingly slower, or the rest intervals need to be increasingly longer, or the HR continues to climb even though the effort is the same, have the mental discipline to stop. YES, TO STOP.  When this occurs, many athletes continue to push, trying to ‘will’ themselves to go faster or farther- to ‘suffer’ unnecessarily. That’s a dangerous game for two reasons- First, we need to be aware that overly high HR, dizziness or headaches, or sudden fatigue can be warning signs of heat distress or even heat exhaustion, which can land us in the hospital. Second, we don’t get any of the adaptations we’re looking for (which happen during our recovery after a hard session) because our body is in such distress that it’s just trying to climb back out of a hole. And if that happens, kiss any adaptations (‘gains’, as the kids say) made in that (or any previous sessions) goodbye. The sign of a truly mentally tough athlete is knowing when to stop and ‘fight another day’. 

So, essentially, when we train in the heat, we need to be willing to make adjustments. To ‘adapt and overcome’, as they say in the military. Using these 6 tips, we can safely and successfully execute even the toughest of workouts in hot conditions, and reap the benefits. Good luck and bring on Summer!