YouTube: SPORTS HYDRATION

Sports hydration involves fluid and electrolyte replacement.  Fluid needs are based on perspiration rates.  We perspire around 1 L/hr during moderate to intense exercise, as low as 0.5 L if it is cool out or when swimming (since water removes heat faster), and up to 1.5 (or even 2) L during very intense training or when it is hot out.  But these are averages; individuals vary a lot.  An easy way to figure out how much you are perspiring is to get on a scale before and after a workout to see how much weight you lose during exercise.  Every 2 pounds you lose corresponds to 1 L or Qt of fluid loss.  If you are drinking fluids during your workout, adding the weight of the fluids you drank to the net loss on the scale will give you your total perspiration rate.  Dividing the amount you drank by total perspiration tells you what percentage of your fluid losses you replaced during exercise.  For every 1% dehydration (1 lb weight loss per 100 lb of body weight), exercise performance decreases 2-5%.  

1 L of body fluid contains 1 teaspoon of table salt, but perspiration contains only 1/4 tsp, leaving 3/4 tsp salt in the body that the body does not want.  In other words, salt CONCENTRATES in the body as you perspire, causing muscle cramping.  As a result, if you are replacing less than half of your fluid losses during exercise you should NOT consider consuming electrolytes during that time.  If you are replacing between half and all of your fluid losses you can consume some salt, but only if you consume all of your losses during exercise should you replace all your electrolyte losses during that time.  Under no circumstances should you EVER gain weight during exercise i.e. over drink fluids, as this can lead to hyponatremia and a trip to the emergency room.  If you eat out after a workout you will be getting more than enough salt to make up for your losses, but if you are eating at home and don't add salt to your meals you may end up falling short on total body salt, forcing your body to urinate out water that it needs for normal hydration.  This process of dehydration from insufficient salt intake after hard training leads to excess urination (no matter how much you drink), reduced digestion capacity, and poor sleep quality.  If you are not eating out and training hard, use 6-12 salt-shaker shakes per hour of exercise with your next meal so that you can properly hold onto the water you are drinking.  

Comments

[James Greenwood]

How would you account for Elite athletes losing up to 10 - 12% of body mass as result of dehydration, and still being able to perform at the levels they do?

Especially in endurance events such as Ironman and marathons?