Hydration

Dehydration is bad for your health and exercise performance. During exercise we only need to lose 2-3% of our body weight before our cycling performance drops 13%. It doesn’t just stop there. The more dehydrated we become the bigger the impact. And it’s not only our FTP or time to exhaustion on the bike that suffers. There are studies that show a decrease in cognitive function, skill execution, and balance. These are not things we want to deal with when cornering at 50 mph! Since dehydration is so detrimental and drinking fluids is so easy a baby could do it, proper hydration should be something that we pay much attention to. Hydrating properly is the easiest and biggest performance enhancer out there.

How much should we drink in general?

We should strive to drink around one ounce of fluid for every two pounds of body weight. If I weigh 200 pounds I need 100 ounces per day. For reference, if you’re ball parking how much you have a day, a regular sized cycling water bottle is about 25 ounces. A Starbucks venti (large) cup is about 20 ounces.

We can easily fine tune that guideline by using the color test. “Pale, odourless and plentiful urine usually means that you are well hydrated.” Anything darker than that means you are probably dehydrated. Completely clear urine might mean you are overhydrating. Adjust your fluid intake accordingly.

Sweating out and absorbing fluids.

When we exercise, we sweat, and therefore will require more intake than the average person. Sweat rate is impacted by many factors including temperature, humidity, how fast we are going, if we are using an ice sock, and exercise intensity. Some research suggests we can lose 1-2 liters per hour at moderate intensities and up to 3-4 liters per hour at high intensities. One to four liters is 34-136 ounces. It is surprisingly easy to lose a water bottle full of sweat every hour.

Just like there is a limit to how many carbohydrates we can absorb per hour, so is the case with fluid. Experts say that the upper limit of absorption is 34 ounces. Maximum absorption decreases below 34 ounces as outdoor temperatures decreases. People who weigh less have a maximum absorption of less than 34 ounces.

How much should we drink during exercise?

We are fighting a losing battle against dehydration in basically every event we do which makes it even more important to take hydration seriously. Our goal isn’t to prevent it but to delay its arrival and slow down its rate.

Past a certain point (up to 34 ounces per hour) fluids will not be absorbed. That’s one reason to make sure to not drink too much. Why carry the extra weight sloshing around? Another more important reason is hyponatremia. Hyponatremia can happen when we are sweating a lot and drinking too much plain water or drinks low in electrolytes. Simply put, this messes with our sodium levels and we can die. (Check out signs and symptoms of hyponatremia.) As the temperature and duration increases make sure to add something to your water that has electrolytes. Many carbohydrate drink mixes contain electrolytes so you may be all set already.

A range that some experts suggest to ingest is 20-25 ounces per hour. A lighter person may be closer to 20 while a heavier person may be closer to 25. If it’s colder you may get away with a few ounces less. If it’s warmer you may benefit from a few more.

Long story short, about one standard bottle per hour is what we are shooting for. I wonder if that’s how they chose the size?

Rehydrate

Even if we fight perfectly we will lose our battle against dehydration. One simple way to rehydrate well is to use your bathroom scale. Measure your bodyweight right before and after your exercise. For every pound you lost try to add 16 ounces to your usual daily consumption. Remember not to drink too much too fast. Hyponatremia.

Total

half of your body weight in pounds + 20-25 ounces per hour of exercise + 16 ounces for every pound lost during exercise

= a good estimate of the total ounces of water/fluid you need per day

If this is a huge increase compared to normal then start slow. Your bladder might need to be retrained to handle the increased input! Another thing to remember is that things like coffee, tea, soup, and cereal all count towards this total. Fruits and vegetables can even help to hydrate you. This is why the equation above is a good place to start but it’s also important to utilize the color test.

A few other points

• If we keep our core temperature down we can reduce our sweat rate. Consider using an ice sock in warm conditions. Using an ice sock can increase our performance in other ways as well.

• When we have more than an 8% concentration of carbohydrate mix in our bottle it starts to reduce the amount of fluid we absorb. It’s important to not put too much drink mix into our bottles. Two scoops of my favorite drink mix is about 60 grams of carbohydrates and total weight. If my calculations are correct, two scoops in my cycling bottle is about 8%.

• I was surprised to learn that the menstrual cycle might not have an impact on whole body sweat rates.