The Physiology of Sports Drinks

I found this article recently, entitled "Sports drinks unnecessary, counterproductive for most people."

Articles like this one from the CBC (Canadian Broadcasting Corporation) are popping up more often in the news media and in gyms, all which have the message of ďsport drinks arenít so useful and possibly harmful, for those engaging in normal exercise.Ē The CBC actually did a blood test trial for a 45 minute run with recreational runners and found that there was not a decrease in the concentration of minerals and electrolytes in their blood Ė some of them actually had an increase.

Whatís missing from many of these articles is an explanation of why sport drinks are unnecessary for the average person.

The first and one of the most important points to cover, is the difference between diffusion and osmosis as it relates to the properties of water. To diffuse something is to spread it out, and most coffee or tea drinkers know that if you drop a lump of sugar into the hot liquid, the sugar will eventually make its way around the whole liquid. In the perspective of molecules, diffusion is when the solid or solute (sugar) moves round in the liquid or solvent (water) from an area where there is a lot of it (high concentration) to where there isnít a lot (low concentration), ultimately, making the concentration even.

What if the sugar is stuck and canít move? There will still be a tendency for the concentrations to even out, but the process is a little different. If youíve ever put sugar on strawberries and then noticed that the sugar gets wet, thatís osmosis. The sugar canít penetrate the cell walls of the strawberries, so the water moves to equalize the concentration.

The second point is something called Signaling. When your stomach is empty, it signals your brain which makes you feel like youíre hungry. Cells in the body do that too. When a cell runs out of fuel, it releases a hormone, thyroxine, which signals the pancreas to produce insulin, which will allow glucose to enter the cell. Adding more and more glucose to the blood, without the signaling, simply saturates the blood as thereís no place for the glucose to go. Itís like ordering one meal at a restaurant and they bring you seven meals. If you only have room for one, what do you do with the other six?

Further to the signaling point, the body has many storage facilities located in various places. Under normal conditions, the body has enough fuel stored to perform its duties without an issue. Itís similar to a car. Driving to the nearest Walmart and back doesnít use a lot of gas so it can be done many times before the tank empties. If you decide to drive from Toronto to Halifax (18 hours non-stop), the gas tank doesnít hold 18 hours of fuel so you have to stop and re-fill. The body has a large enough tank to fuel a one hour session at the gym, but not enough for a t twenty six mile marathon.

Finally, the research is indicating that a person can sweat out up to ~5% of its body mass before there are performance variances (this is before drinking anything). So if a 150 pound person is working out at the gym, there wouldnít be any energy or strength changes until he/she has lost ~7.5 pounds of sweat. Thatís 3Kg, or 3 jars worth of peanut butter. For someone working out at a medium intensity for an hour, there is a low chance that they would lose 5% of their body mass within an hour, but if they were working at a high intensity for 2-3 hours, then 5% loss is more believable.

So what happens in the body is that when someone is exercising or engaging in sport, they sweat. As the activity continues, electrolytes from the storage areas are utilized. Once the body has lost enough electrolytes and water to result in performance loss, the cells signal the brain and other organs that they need more fuel.

How does all this fit together??

Just like the sugar on the strawberry, if someone consumes a sport drink after walking from the bed to the couch, then thereís so much sugar, salt, and other minerals in the blood that water is drawn out of the cells and into the blood where it will be filtered out in the kidneys Ė essentially dehydrating the person. If the cells are signalling that they need fuel, and a sport drink is consumed, then the cells will become replenished, and the body will have more water to sweat out.

Dan