Fasted aerobic workout – duration?

  • Creator
  • #40982

    I’m following the 16 week Eiger plan. It says to do all Z1-Z2 aerobic workouts fasted. The duration of these goes up to 6 hours. Is the goal to do even these fasted?

    Up till now my longest fasted run was ~2.5h, and I’ve had snacks if it goes longer than that. Last weekend I ran a marathon distance training run, and as a test I did it completely fasted and didn’t snack during. Took me slightly less than 4 hours, and I was surprised that it worked well fasted – got really hungry around the 3 hour mark, but the hunger subsided in a few minutes and I was fine for the rest.

    I see obvious benefits of fasted running/hiking for shorter runs (~2h) and have read the studies cited in the book. I’m wondering whether there are any risks involved when doing it on much longer runs – e.g., longer recovery needed or possible getting weaker overall because of insufficient nutrition during those long efforts? The first thing I do right after is to refuel a lot of carbs, so maybe that prevents any negative side effects, but I’m still wondering.

  • Participant
    Kyle Brundage on #41055


    I would strongly suggest checking out this thread over on Nutrition and especially Rebecca Dent’s comments:

    I hope they will answer your question; that much longer runs require longer recovery and possibility of detraining/growing weaker from the duration. I also copied Rebecca Dent’s response below:

    “What are you training for? I would suggest that 2.5hrs is a good time to be able to carry out training fasted, what is the purpose of pushing it further? In the main event the goal is not to see how far you can go and not eat, the aim is to make you more fuel efficient for the main event (and eat during the main event). The training you are carrying out fasted at the moment is still going to be having an influence on fat adaptation and endurance performance, it comes back to consistency over time. Also be aware that fasted training increases the stress on the body e.g. on the immune system /increase muscle damage, increase fatigue, so I would caution against pushing the time you can carry out fasted and the negative impact this can have, it’s about striking a balance. You need to be able to put in good quality training for your other sessions (that also count towards your performance) and not increase day to day fatigue which may also impact your day to day energy levels and motivation to study.”

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