• Question: How much sport can your body do before ingesting carbohydrates? I mean you wake up in the morning and start running, (supposing you are going slow enough for not getting tired after 1 minute) when do you have to get some energy?

    Asked by Luigyvalls to Andrew, Dan, Emilia, Helen, Katy, LauraAnne, Stephanie on 8 Nov 2016.
    • Photo: Dan Gordon

      Dan Gordon answered on 8 Nov 2016:

      Interesting question. Lets assume you have gone to bed and just woken up and gone for a long run. Over night you would have restored any carbohydrate that was lost during the previous day (assuming you ate carbs for dinner). Now though after this run we could assume that around 25% of the stored CHO is used up. If we don’t now consume anymore for the rest of the day and do the same again the next day, we would be looking at the same response. However this time we would be using 25% of 75%, and so on. There was a very famous study done in the 1980’s by a physiologist called David Costill who double the volume of swimming training overnight but did not alter the amount of calories ingested. He showed a significant decrease in the stored carbohydrate in muscle (glycogen) after each session. Interestingly a number of swimmers could not complete this 9-day protocol because they had in essence depleted their glycogen stores.
      So if we look at hard facts, you could maintain a steady pace of around 160 bpm for 90 mins before you have depleted the CHO stores, but were you to reduce the intensity you could continue for much longer.

    • Photo: LauraAnne Furlong

      LauraAnne Furlong answered on 9 Nov 2016:

      I can’t top that physiological explanation from Dan, luckily athletes will usually have some carbohydrate as part or as all of their dinner the night before, i.e. they will have some pasta or some sweet potato or rice or similar, so they will wake up in a some sort of state where they can exercise straightaway.

    • Photo: Emilia McAllister-Jepps

      Emilia McAllister-Jepps answered on 13 Nov 2016:

      This is a great question! I can’t compete with Dan’s answer, but would also add that there may be some instances where an athlete may be working on a calorie deficit in order to achieve or promote a physiological response. In some sports, when an athlete may be trying to become leaner, they may increase their protein intake and decrease their carbohydrate intake. A good example of this can be seen amongst body-builders. But it is not something I would recommend doing, when the body has low glycogen stores the body becomes less capable of coping with training load.

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