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Thursday, September 24, 2015

“Reduce your salt intake! No simple sugars!” – Heard this before? Well Not Necessarily If You Are An Athlete!

You may need to add these two unlikely nutrients to your training regime if you are exerting yourself with prolonged intense aerobic exercise of 1 hour or more.

We as humans rely on fluid intake to maintain total body water and blood volume.
Dehydration limits the ability of the body to increase skin blood flow for the purpose of transferring heat from the body core to the skin surface.  When the blood volume decreases, the heart needs to pump more often to get the same amount of blood to the working muscles.  Mild dehydration can impair performance, whereas significant dehydration can put a strain on cardiac output as well as jeopardizing the ability of the body to maintain core temperature within safe limits during exercise.
*2% dehydration may cause performance to be decreased by 3-5%, at 4% dehydration your capacity for muscular work declines significantly.

If you were to do the math, a 50kg female would only have to decrease her weight by 1kg to equal 2% of body weight and impair performance.
Perhaps she races 10km run in 60 minutes. A 2% dehydration can cause a performance decrease of up to 5%...
So 60min x 0.05 =  3min  … making her time 3min slower to 1:03 !!

The table below adapted from the ACSM Position Stand on Fluid Replacement in Exercise, shows how large the ranges are for sweat rate even within the same sport. 

Ranges of Sweat Rate (l/hr)
Ironman Triathlon
Bike Leg (Males and Females)
0.47 - 1.08

Run Leg (Males and Females)
0.4 - 1.8
Half Marathon Running
Winter Competition (Males and Females)
0.75 – 2.23
Summer Training (Males and Females)
0.74 – 2.92
American Football
Summer Training (Males)
1.1 – 3.18
Summer Training (Males)
0.99 – 1.93
Summer Competition (Females)
0.56 – 1.34

Fluids Needs in Training
Athletes generally need between 500ml (less intensity or smaller person and cool) to over 1500ml (high intensity or larger person in the heat) of fluid replacement per hour, but this will vary greatly between individuals, exercise intensity, and environment (temperature and humidity).  Try weighing yourself before and after your exercise in various conditions to determine the amount of fluids you lose in your sweat while training.
*Drink enough to prevent dehydration of more than 2% of body weight but do not drink more than your sweat rate.

This is a rare but serious condition when an individual participating in prolonged (over 5 hours typically) endurance exercise has a very low concentration of sodium in their blood.  This can be the result of excessive water consumption without enough sodium replacement, but can also occur simply due to a high sweat rate and high concentration of sodium being excreted in the sweat without enough sodium being replaced by a sport drink or other source.  Athletes engaging in extremely long endurance events need to be aware of their needs for electrolyte replacement to avoid this scary or even deadly medical condition.

Sodium Needs in Training
Every individual has different sweat rates as discussed previously, as well as different concentrations of sodium in their sweat.  You might know you excrete more than the average person in your sweat if you are visibly covered in salt by the end of a race or training session.  The average person needs 300 to 600mg of sodium per hour to maintain blood sodium concentrations, however a very “salty sweater” may need even more than this.
*For exercise sessions lasting longer than an hour, a sport drink with appropriate electrolytes and carbohydrates is recommended.  A properly balanced sport drink will decrease urine output, enable fluids to empty quickly from the stomach, promote absorbs ion from the intestine and encourage fluid retention.

Carbohydrate needs in Training
While training for over an hour or an hour and a half, athletes will empty their stores of liver glycogen and muscle glucose, therefore they will need to replace this with easy to absorb carbohydrates.  Simple sugars such as glucose, fructose, dextrose, or maltodextrine will provide the immediate fuel for the athlete to use for optimal energy and training performance when exercising for prolonged periods of time.  Athletes training for sessions of 1-2 hours will need approximately 30 grams of carbohydrate replacement per hour, whereas those enduring longer sessions will be able to use 60 to 90 grams of carbohydrate per hour. 

Carbohydrates Required for Optimal Performance
Carbohydrate type
Less than 1 hour
Very small amounts
Most forms of carbohydrates
1-2 hours
Up to 30 grams per hour
Most forms of carbohydrates
2-3 hours
Up to 60 grams per hour
Carbohydrates that are rapidly oxidized such as glucose and maltodextrine
Greater than 2.5 hours
Up to 90 grams per hour
Carbohydrates thatbare rapidly oxidized such as glucose or maltodextrine in combination – must be more than one type of carbohydrate

Sports Gels verses Fluid Electrolyte and Glycogen Supplements

A brand new research study has found that replacing carbohydrate and electrolytes through consumption of a gel or a sport drink type fluid shows no difference in the performance of endurance triathletes.  However, the study did show an increase in gastrointestinal distress in athletes who used the gel.  Therefore it might consider this a disadvantage to gels over a sport drink fluid.

- Sheryl Ross M.Kin, Sports Nutritionist, Infinit Nutrition Canada

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