Running: Hydration and Energy – a bit of the science behind it


I had posted this to a question on a running forum in reference to a discussion on what to use during the Mumbai Marathon this year – Gatorade or Gel or both – and running hydration in general. The issue came up after it was announced that Gatorade was the new official energy drink partner for SCMM 2012. Hope this helps in understanding the issue a little better.

Yes, the key is not to take both Gatorade and an Energy Gel/Bar together during a marathon. Here is, “hopefully”, a simplified explanation –

Most nutrients are absorbed in the small intestine. The small intestine absorbs nutrients best when they are in an isotonic state (that is the concentration of water to dissolved nutrients is similar to that in the body). If they are in hypertonic state (more concentrated than your body fluids) the body will need to dilute them and therefore it will draw water from the body/cells to get the food/drink into isotonic state. A hypotonic liquid (something like plain water) will also be absorbed quickly but mostly in the large intestine. For those of you who remember your elementary school science this is nothing but the principle of osmosis in action (the lining of different parts of the intestine being of varying permeability will play different roles in the digestive process).

For short duration exercise where you don’t lose a lot of salt and water just using a hypotonic solution (plain water) is enough. For long endurance events where you deplete salts, water and stored glycogen you need an isotonic “energy” solution from which nutrients can be extracted early in the digestive process.

Gatorade is an isotonic energy drink and therefore already in the right concentration to be absorbed in the small intestine. If you have a gel (nothing but an energy drink with the water taken out) and then also drink Gatorade with it, the resulting solution is hypertonic and will start drawing water from your body before the nutrients can be absorbed. Therefore if you are going to use both then alternate between the two (with at least a 30-45 minute gap) and with each gel/bar drink at least 200-300ml of plain water (if not at one go then in a span of 10-15 minutes post gel ingestion). If you don’t drink water with the gel/bar the body is going to draw that water from you leading to eventual dehydration.

Personally I would recommend using just one (Gel/Bar or Gatorade) during a run so that it is easy to keep track of what you are doing. Gatorade would be ideal (already isotonic) but it would be really cumbersome to carry enough of it for your entire long run compared to pouches of gel.

A lot of marathons (including Mumbai earlier with Lucozade) only serve up isotonic “calorie free” drinks which are great for replenishing salts & water but will do nothing to replenish glycogen levels. So watch the label of what you are drinking if you also want energy.

BTW a very simple near isotonic energy drink would be a standard unsweetened juice (Real Active, 100% Tropicana, etc), a pinch of salt with water added to it in a 1:1 ratio. A good and cheap gel could be as simple as a tube of jam (Kissan sells tubes of jam) with maybe some salt (some jams have salts other don’t).

Hope this clarifies.

Very best for the final two weeks of training before SCMM 2012.

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About Sandeep

Consultant, Mentor, Headhunter & Leadership Evangelist.

Posted on January 3, 2012, in Energy Gel, Extreme Running, Hydration, Mumbai Marathon and tagged , , , , , , , , , , , , . Bookmark the permalink. 1 Comment.

  1. Francis fernandes

    Well explained and thanks a lot !

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