Fasted easy runs | 80/20 Endurance

Fasted easy runs

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    Leyla and Matt, thanks for your thoughtful, comprehensive answers. I will definitely pass it on to my daughter. I really enjoyed your books. They have changed the way I approach cycling in running.


    Is there any credible research into how the adaption takes place? I’m skeptical that a couple of depletion runs during the final weeks of race prep have have enough time to engender the adaptions beyond testing the ability to suffer. Indeed Matt’s article points out that there is no evidence of improved performance.

    To the contrary, in my own case as an older runner there is research confirming that recovery is compromised during depletion runs. It may be be beneficial to do depletion workouts in the months before a training segment for master athletes if they truly give a long term advantage. I can’t help but think that it would be better use those few precious weeks prior to a race to keep everything performance based with quality endurance runs and do the suffering at a quicker pace.

    Matt Fitzgerald

    Planned and executed correctly, depletion workouts don’t cause any more “suffering” than any other workout. The planning part is a bit challenging in readymade plans, but I am always careful to prescribe a duration that an athlete should be able to handle fairly comfortably given the fitness they’ve built through the preceding training. For example, if you can comfortably complete a three-hour ride with normal fueling, you should be able to complete a two-hour fasted ride without any trouble. I don’t know why people think these workouts are so extreme; they’re just not.

    My own use of fasted workouts supplied experiential evidence of a benefit. In much the same way you know your mobility routine is working by the fact that the stretches get easier, I knew my fasted workouts were benefitting me by the fact that I could go longer and longer without fueling before reaching the same level of fatigue. And this despite the fact that I didn’t do them very often.

    Up to this point, the research on fasted workouts has used protocols that, while illuminating, don’t really translate to real-world training. In the most recent study, cyclists performed the following protocol three times per week for three weeks: afternoon HIIT workout followed by low-carb dinner, sleep, low-intensity workout in the morning before breakfast. Overall carbohydrate intake was held steady throughout the week; only the timing was manipulated on depletion days.

    On average, FTP increased by 5.5 percent in experimental subjects compared to 1.2 percent in control. So there’s your benefit. But as a coach, am I going to have athletes do three HIIT workouts every week? Of course not. However, in future iterations of our Level 2 and Level 3 plans, I might insert a note in certain HIIT workout cards inviting athletes to do the workout in the afternoon, following it with a low-carb meal, and do the next day’s low-intensity workout before breakfast if they so choose (while maintaining normal levels of overall carb intake on both days). I think this method might feel less extreme to athletes for whom the long depletion workouts do feel extreme. It certainly didn’t feel extreme to me when I did it, but then again the long depletion workouts didn’t either.

    In the meantime, I am reasonably confident that depletion workouts are integrated into our plans in a way that supplies a small net benefit for most athletes. If you feel this is not the case for you, you might try shortening the workouts a bit.


    I can’t speak for others but personally, I don’t find fasted aerobic range workouts to be extreme or difficult. My bias comes from the fact that I have self-experimented with fasted workouts and intermittent fasting more generally and found them to yield little benefits, seemingly reduce my metabolism in the short-run, and be a pain to plan around. I would prefer just to go an extra half hour in a normally fueled run which also generates that “dead leg” feel that clearly signals a depleted glycogen state.

    But it is good to have an extra tool in the training toolbox so that if I am time constrained, I can just do a fasted shorter run rather than a longer normal length run or ride.

    Matt Fitzgerald

    I should have mentioned previously that the effect of an overnight fast on endurance performance has been studied and it comes to about 3-4%. That’s it. Not exactly extreme.


    For what it is worth:
    I follow a low to moderate carb diet.

    I do all my runs fasted. Some electrolytes without any sugar/carbs is all I use for long runs. (Experimented with some gel intake during long runs, but abandoned it, because it didn’t have any added value to the performance.)

    I never encountered any issues training this way. I guess, building up your running volume with no more than 10% per week, can make you rather fat-adapted pretty soon. Possibly it also has to do with your body-type whether this will work for you, or not.


    Hi all, great thread here-
    so as a busy person who admittedly (often) does not fuel up/top-off before low intensity foundation/recovery runs (usually 35-50m duration), is there a # of grams of carbs that you would recommend I proactively have around convenient to grab (ie jelly bellys, or honey) 15-30m before a run without causing major stomach cramps?


    JB yes it’s called a banana 🙂

Viewing 8 posts - 16 through 23 (of 23 total)
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