Studies have shown that marathon performance in 75 degrees negatively affects performance by 7% and at 85 degrees by 10%. There is a metabolic response to exercising in the heat that includes increased sweat loss, resulting in the heart pumping less blood; therefore less blood is being delivered to the muscles. In addition, with less oxygen there is an increase in lactate levels; while our individual level of fitness can determine our ability to efficiently clear lactate, it may affect muscle contraction and overall performance. In addition, your body’s core temperature rises and your heart rate increases as it works to compensate for the dehydration.
The good news is that adaptation can occur. It can be a constant evolution to discovering what is ideal for our situation; even the elite’s make mistakes, learn, and go back to the drawing board for moving forward. After struggling with dehydration at the Olympic Trials, Shalane Flanagan knew that she needed to reevaluate her race nutrition and hydration strategy going into the 2016 Summer Olympics in Rio. If interested, you can read more about this here. While the majority of us do not have access to the technology and individual scientific studies of experts in the field, there are steps that we can take to dial in our individual hydration profile.
What can we do to adapt and minimize risk?
The good news is that you will acclimatize to the heat. Studies show that this adaptation can start happening in a few days, but full adaptation make take a couple of weeks.
- Wear clothing that wicks moisture and helps regulate core temperature. Some garments will have an SPF in the fabric. Wear a cap with a brim to keep your face shaded. Use sunglasses to guard your eyes from harmful UV rays
- Adjust pacing- this is a time to slow down to offset the lower oxygen debt and lactic acid thresholds (for about the first three days in the heat); If you have not had time to adapt to the warmer temperatures, the first thing to do is slow down. Talk with your coach about calculating a new pace range based on race-day temperatures.
- Proper fueling: Hydrate and increase your carbohydrate intake to counteract the glycogen depletion. Make sure you are drinking regularly throughout the day. Know your sweat rate and hydrate regularly and early during your run. (See Calculating your Sweat Rate and the Basic Hydration Chart below).
- Adjust your workout times to go earlier in the morning before temperatures are highest and sun is most intense. If you will be racing in the warm temperatures, you may want to sprinkle in some heat training, but you don’t want to jeopardize the quality of all of your workouts by dong them in the heat.
- Find the shade: go to the tree lined side of the street, run in wooded areas
- Wear sunscreen to reduce the chance of a sunburn which will further complicate things
- If you are weighing yourself before and after your workout and know your fluid loss, you will want to replace each .lb lost during exercise with 2.5 cups of water (20 oz.) Not all at once, as our bodies can only process about 4 cups (32 oz.) an hour; this also might be a good time to add a pinch of sea salt to your water. Water follows salt, and the salt is going to aid re-hydration at a cellular level.
Calculating Your Sweat Rate
- Weigh yourself prior to your run and convert your weight to ounces (16 oz. per lb.)
- Exercise for 60 minutes without urinating and track your water consumption.
- Weigh yourself post-run and convert your weight to ounces.
- Subtract your post-workout weight from your pre-workout weight, add the number of ounces you consumed. And the remaining number will be your sweat rate per hour.
- For accuracy, you will want to do this in varying temps.
There are a number of sources to get your electrolytes. Again, not all agree with everyone’s chemistry. So during training is the time to experiment. Below we list some options, but there are many more on the market to choose from and some athletes create their own.
As you are experimenting during training, these are warning signs that should not be ignored or pushed through:
1) Heat Cramps: muscle cramping, beginning to notice thirst, profuse sweating, and fatigue
2) Heat Exhaustion: Weakness, pale and cool skin, fatigue, profuse sweating, and thirst,
beginning to notice early signs of faintness or dizziness, cessation of sweating, chills or goose
bumps, headaches and nausea
3) Heat Stroke: Confusion, hot and dry skin, strong and rapid pulse, faintness or dizziness,
cessation of sweating, chills or goose bumps, headaches and nausea
A safe plan is to be patient in allowing your body to adapt and slow down, drink to your sweat rate and with the right balance of electrolyte to water based on your needs, don’t let it “get in your head” that you are needing to slow down, and don’t ignore any warning signs.