Sports Nutrition – During Exercise 614 411 Visual Veggies

Sports Nutrition – During Exercise

This article is Part 2 of a series of three articles.  Last month’s article covered Sports Nutrition – Before Exercise, and next month’s will cover Sports Nutrition – After Exercise.

Sports Nutrition – During Exercise

Keeping with the article trend for summer, this month’s article focuses on sports nutrition specifics for use during exercise.  Some key items we will be covering here include fueling, hydration, stomach comfort, and factors, such as exercise duration and climate.

Fuel the Activity!

Every movement and activity the body does requires energy.  Even while you’re sitting here reading this article, your body is needing fuel for your heart to pump blood, while you hold your proper posture, your stomach digesting that Greek yogurt you just ate, and every other involuntary action happening in your body.

But what is the body burning for energy?  In a sedentary state (such as reading or watching tv), the body is burning a higher percentage of calories from fat, some carbohydrates, and a very little protein, though not a lot of total calories.  Now if you put the book down and take a brisk walk, you would be burning a slightly lower percentage of fat calories, a bit more carbohydrates, and a tiny increase in protein.  Finally, you lace up your shoes and go out for a high intensity run, and your nutrients burned for energy shifts to mostly carbohydrates, less fat, and still some protein.  The latter is the basis of this article, and the emphasis on energy needs during exercise is on carbohydrates as explained below.

We store carbohydrates in the muscle cells in the form of glycogen (glycogen is also stored in the liver, but that is another story), which can be thought of as tiny fuel tanks.  In a properly-fueled athlete, the amount of glycogen can carry his energy needs through roughly 90 minutes or more of exercise without supplementing with exogenous carbs.  After the fuel tanks run out, the athlete needs to stop the activity and replenish.  Runners call this “hitting the wall”, and to cyclists, it’s known as “bonking”.  To prevent this glycogen depletion, it is recommended to consume carbohydrates throughout the activity.

If the activity is 60 minutes or less, carbohydrate consumption is not necessary, but also not harmful if taken during this period of exercise time.  Workouts lasting longer than 60 minutes require continuous fuel to maintain the high energy needs and prevent fatigue.  Previous recommendations suggested taking in 60 grams of carbs per hour of exercise as the maximum amount that can be tolerated.  More recent data (Currell 2008 and Triplett 2010) illustrates that the maximum amount of carbs taken during exercise can be increased to 90 grams per hour when taken in a 2:1 ratio of glucose and fructose, utilizing separate transport systems.  Individual needs will vary, and athletes should be encouraged to practice their nutrition strategies during training and perfect them for race day.

Athletes can use various types of sports nutrition products to meet their energy needs, including sports drinks, gels, carbohydrate chews, fruit purees, and sports bars.  There are so many types of products from which to choose, and they can be mixed and matched based on individual preference and tolerance.  For example, products with only simple carbohydrates might be preferred for athletes who run as this will leave the runner less susceptible for stomach discomfort.  Cyclist might utilize the time on the bike to opt for products that contain some complex carbs and protein for long-lasting energy.  Athletes engaged in team sports who have downtime between repetitions can go for fruit or carbohydrate chews as these provide simple carbs yet need to be chewed.  However, there is no one answer for all athletes.  Runners may decide to consume bars, and cyclists may need to stick to liquid nutrition.

Stay within the Hydration Zone

Dehydration may be one of the most devastating issues for athletes as this can greatly impair performance and also be very dangerous.  It is important for athletes to know their sweat rate when exercising and match their fluid losses with consuming adequate amounts of water or sports drink.

What is the Hydration Zone?
The Hydration Zone is an amount of allowable weight loss an athlete can have, yet still be considered adequately hydrated.  A weight loss can occur during exercise from fluid losses, and a loss of more than 2% of the starting bodyweight is indicative of dehydration.  For example, an athlete who starts an exercise session at 150 pounds should lose no more than 3 pounds of water weight by the end of the workout session.

Conduct a Sweat Rate Test
Conducting a sweat rate test is an easy way for an athlete to prevent dehydration in future training sessions and races.

  1. 1. Weigh yourself before the exercise session
  2. 2. Exercise for one hour at a moderate to high intensity
  3. 3. Drink as you normally would and keep track of how much
  4. 4. Weigh yourself after the exercise session
  5. 5. If you lose more than 2% of your starting bodyweight, perform the test on another day but with taking in more fluid
  6. 6. Continue steps 1-5 until you achieve a weight loss within your Hydration Zone

Final Thoughts on Hydration
The sweat rate test is an easy and reliable tool to determine an athlete’s fluid needs on an hourly basis.  But a quick and dirty method for evaluating one’s hydration status is the color of the urine.  Urine should be light yellow, resembling lemonade.  If the urine is dark, like apple juice, drink more.

Let’s say a hypothetical athlete’s fluid needs were figured out to be 32 fl oz per hour.  The best approach to achieve this high amount of fluid each hour is with small, frequent sips.  Large amounts of fluid taken at one time could lead to a sloshing feeling in the stomach.  When I consult athletes on hydration, I advise them often to get on a drinking schedule (this can also be adopted for their energy needs).  Most athletes will wear a sports watch with tons of features.  One common feature is to set a reminder every XX minutes.  This hypothetical athlete can plan on taking 2-3 large sips every 10-15 minutes, which would be more manageable and also remind them to drink, even when they’re not thirsty at the present moment.

Lastly, climate should be taken into consideration with hydration.  The hypothetical athlete lives in and trains in the northeast, and the training months are in the winter/spring.  This athlete will be traveling to a hot and humid climate, such as Florida to compete in late spring/early summer.  If he performs the sweat rate test in Maine in early spring, his fluid losses will vary greatly when he actually competes in the hot Florida sun.  In order to match his losses when racing, he should plan on consuming more than what he was taking during training.

See also:
Sports Nutrition – Before Exercise
Sports Nutrition – After Exercise

Currell K, Jeukendrup A.  Superior Endurance Performance with Ingestion of Multiple Transportable Carbohydrates.  2008
Triplett D et al.  An Isocaloric Glucose-Fructose Beverage’s Effect on Simulated 100-km Cycling Performance Compared with a Glucose-Only Beverage.  2010