I have to be honest with you. I have never “bonked.”
I’ve read about it, heard people describe it, and believe me I’ve felt all kinds of ridiculous pain around mile 20 of a marathon, but, I’ve never bonked or “hit the wall.”
While I can’t say for certain why I’ve avoided it, I do think my fasted morning runs haven’t hurt the issue. I have almost always run fasted in the early morning because it’s been convenient, I’m never hungry that early, and in the past I was always trying to avoid having GI issues on my run and less food equaled less chance of a problem for me.
In the beginning, I had no idea what glycogen was or that I had inadvertently been training myself for long distance success by running in a fasted state. All I knew was that I felt great on my runs and was perfectly fine to save breakfast until afterwards.
It wasn’t until I started reading about the science behind running that I realized I had been teaching my body to burn fat more readily over long distances and maintain my pace more easily.
What It Is
“Glycogen depletion training” is really simple: you don’t fuel, or you cut way down on fuel, before and during a longer run, with the purpose of training your body to use its own fat for fuel more easily.
If you’re training for a marathon, your long runs already have this as one of their goals, because anytime we run more than about 1.5 – 2 hours, we are going to have to use some of our fat for fuel. If your body is not used to this and can’t burn its own fat efficiently, you will inevitably slow down and possibly “hit the wall” or “bonk” right around 2 hours into your run. Or so the legend has it! Okay kidding, it’s not a legend. There is science behind why this happens.
When To Do It
Since your body can use stored glycogen for about 1.5 hours, it makes sense to do this type of run when you will be running about 2 hours or a bit longer. I do this type of long run earlier on in marathon training when my weekly long runs are 14-18 miles and I don’t need to practice my fueling strategy just yet. I have done this for 2 or 3 runs per training plan. I also only do this if the run will be at an easy pace (no marathon paced middle miles) since at faster paces our bodies will require more sugar.
And since the goal here is endurance over a long period of time, I believe it is only truly beneficial to do this type of training if you are preparing for a marathon or ultra, rather than shorter distances.
When Not To Do It
Don’t do this for speed work, tempo or marathon paced runs, or long runs near the peak of your training since at that point, fueling as you will on race day will be more important for your training than teaching your body to burn fat efficiently. If you have done some fasted runs earlier on in your training, your body should be pretty skilled at using fat by this point!
Why Do This?
You don’t have to train fasted to be successful in a marathon, but if you have had issues in the past with “bonking” it is probably a good idea to incorporate fasted training into your plan to improve your ability to use your own fat for fuel. It won’t make you faster, it won’t make you lose weight, it won’t make you a better runner with superpowers – BUT it will help your body learn how to turn its own fat into energy while maintaining a certain pace. So, even when you are fueling normally during your marathon your body will not “burn through” sugar as quickly since it will be using fat as well, and “saving” sugar for the times you need to kick.
How Do I Do it Without Starving?
First thing in the morning is the best time, because you haven’t used up much energy at that point just by being awake and you probably aren’t as hungry/tired as you would be later in the day. If it’s the first time you’re trying it, bring along fuel “just in case” or just start off with shorter runs to see how you feel. It’s not for everyone, and if it doesn’t feel right, there’s no reason you need to do it!
- Hydrate as much as usual! Make sure you drink lots of water! No need to be dehydrated along with lacking fuel. Hydrate the night before and the morning of, and bring along water as you normally would.
You will need to plan your after-run refueling more carefully. Your body needs carbohydrates and calories to help it recover from a long run, and this is especially important if you completed your run in a fasted state. Make a carb-heavy smoothie (something simple like coconut water or almond milk with bananas) to have within 20-30 minutes of completing your run. Or if you’re lazy like me just shove bananas and coconut water directly into your face after your run. About an hour later, or sooner if you’re hungry, have a large meal consisting of carbs, fat, and some protein. You may feel a bit more tired after this type of run than others, so plan to rest accordingly.
Like I said earlier, THIS IS NOT ABOUT GETTING FASTER OR LOSING WEIGHT! It’s simply about the utilization of fuel. Here are links to some websites for further reading:
Have you tried glycogen depletion training? Have you ever “bonked” in a marathon? Are you happy with your current fueling strategy? What has been your experience running in a fasted state?
Reader Reviews & Comments
Great post. I have bonked before, but it was because I was just unprepared as a result of having to work an unplanned double shift the night before and thus not being able to hydrate and fuel properly. I’ve reached some mental walls, but I think that is more typical than a true and utter bonk.Once you do bonk, though, you work very hard to make sure that it never happens again!
I have definitely had mental struggles that’s for sure! But my body kept going. From what people say it’s definitely something you wouldn’t want a repeat of.
Linda @ Fit Fed and Happy says
That’s the great thing about keto–I don’t run out of fuel because I’m fueled by fasts instead of glycogen!
It’s amazing what our bodies can do!
Lisa @ Running Out Of Wine says
Great info! I definitely bonked during my marathon last fall. I remember being on pace for like 3:45 and then at mile 16 it was all over. I had to walk a little bit each mile just to finish. I remember taking any kind of fuel that was offered on the course…even swedish fish! (won’t do that again). But I’ve been doing my shorter easier runs fasted lately. I’m a little nervous to go out fasted for long runs, but since tomorrow I’m doing 13 before work, I’m considering it since I’ll be starting so early. Im sure I’ll bring fuel along just in case. Any idea how coffee before running impacts all this?
That sounds like a terrible bonk but along the lines of what others describe. I have never been able to drink coffee before running because it bothers my stomach, so not sure on that one. I would think caffeine wouldn’t have much effect after the two hour point though. For a 13 you should be fine, but definitely bring fuel with you if it’s the first time trying it. I may do my 14 this weekend fasted. I have to look at my schedule and figure out what makes sense.
I always thought the bonk was a myth until my last marathon. Mile 22 on and my legs wouldn’t move. I wasn’t tired or hurting, but my legs would not move. It was the strangest thing. I have to do a combination of your recommended training and carb loading. Coconut water is incredible! I have been hooked on it the past four months. Great article!
That’s really what I’ve heard people describe with it! I remember a guy chatting during a marathon and talking about his last bonk, and it just sounded unreal, he was going from targeting 3 hours to unable to run at all after 20. Glad you enjoyed this! And coconut water is now my “sports drink” and I love it 🙂
Megan @ Meg Go Run says
Thank you for providing those links at the end! When I run before work, like you I am not hungry. I have no problem getting through a 4-6 mile run without fueling up beforehand. But I totally eat my face off after. I don’t run in the fasted state for any other purpose than not being hungry. So it is interesting that it could in fact be helping my body learn to burn fat. On days I don’t work, I don’t get up as early and I wait longer to run. This includes long run days. I definitely need to fuel up then because I was awake for too long and my stomach is empty. My “bonking” at the end of a marathon is defined by my quads burrrrrrrrrning due to lactic acid build up. This does not happen during every race, and it happened more often during my early days of running. It is a horrible, painful feeling! It happened to me at like Mile 11 at Boston this year because I pretty much ran farleks the first third of the race. Oops lol.
Boston was rough this year, if I was going to bonk in a race that should have been it. And it wasn’t easy but no bonk 🙂 I am going to do at least one 16 and one 18 fasted for my training and the rest of the long runs I’ll be practicing fueling. Sounds like you burn fat pretty well though, everyone is different with this it seems.
Erica House (@Erica_D_House) says
I hit the wall on a training run during my first marathon training. I think it was an 18 miler – first time I had gone that far – at at mile 16 my body just gave out. I was hyperventilating from crying and wanted to pass out. I walked the last two miles. I was actually glad it happened so I knew what to expect, and how to handle it better, should it happen on race day!
Much better to experience it on a training run, as much as it sucks! Surprises like that are never welcomed on race day! Sounds like a bad experience though and along the lines of what I’ve heard from others.
Reading this sort of gave me some deja vu! When I first started running, I was just running for fun and to prove to myself I could, and more than anything stress relief. I had a small business and had no life or time, so my training was literally my time to de-stress. Since I always ran early in the morning, I never ate anything, and then ran my first couple of half marathons without anything at all but water… holy crap, I laugh at how much more I’ve learned since 2007! I’ve been around some extreme opposite people/friends that believe in fueling every minute, before, during and after. When I started my first Paleo marathon training in 2012, I only used fuel for long runs and it seemed to really help, and made sure I had my recovery drink/food after. I’ve gotten lazy again – I can easily run for 1-2 hours on nothing but water and then not be hungry for 2-3 hours. Not good for recovery! but then suddely it hits me and I’m HANGRY. oops 🙂
We have a lot in common! I’ve also had a friend that thought I was nuts for not bringing fuel for 12 miles. For me 12 miles is just not long enough to need fuel and I’ll only bring something if I’m practicing a fueling strategy. For me though, after I run within a half hour I’m starving! Not in the past though when I had stomach issues. Then I’d put off eating a lot and only be ravenous later on or the next day which didn’t work for me. I like being able to refuel well within a couple of hours of a long run.
Totally, that’s why I read your blog – you have influenced me to eat much more healthfully and be on top of my recovery fuel.
About running with/without fuel again – yes totally agree. 12 miles in my head is like 2 hours and since I am a slower runner I never felt the need for fuel or even hungry. Even when I ran faster it didn’t hit me. Since I used to do all my training and running solo, I never had anyone to compare myself to or look at for nutrition guidance, which was good and bad. I naturally didn’t want food before my run in the A.M., and afterwards had to rush to work.
When I joined a running club I was in for such a shock but also learned a lot 🙂
Running always teaches me something new every single time
I think early on if we feel fine we just keep going, not realizing how we should be taking care of ourselves. Or, like me, we think we have superpowers 🙂
Okay I’m being a total dork by replying here (again) but I just really felt like sharing this with you since you sort of inspired me yesterday to have the BEST run of my life! lol okay well at least this year 🙂 After this post and our little banter I decided to really go and see if I could run like I used to, just wake up on a nice Sunday while the guys are out golfing and RUN. So yesterday I got up, drank some water, prepared my self with water, and took off. For 2 hours! For me that got me 11 miles of running and a mile of walking. OMG!!! I felt so amazing on just water – and I haven’t run beyond 7 miles in months!!! I’m so happy, you totally inspired this and I don’t have that many people to share this stuff with – my close friends and family are so TIRED of hearing about it I just want to spare them. Anyway, thank you so much reminding me of what I love. You rock!
Thanks! I’m so happy to hear you had an amazing run, it’s definitely a great feeling! And I totally get you telling me over the fam – mine glaze over when I start talking about running more than just a number of miles 🙂 Thanks for sharing!
I’ve never run a whole marathon only halfs but have hit a few lows during trainings. Never on an actual race though. If I ever do a full marathon I’ll definitely give this a try!
Training is definitely the time to hit lows or experience problems. Lots of learning happens in training and it’s not always fun to say the least! Something to think about for marathon training.
Beth @ Running with the Sunrise says
Interesting post! I’ve read about glycogen depletion training but I’ve never been brave enough to try it during my own training. I just get so hungry on my long runs. I’ve done a little bonking during a marathon (where I feel like I’m working super hard to maintain the same pace), but I haven’t gotten to a point where I can’t keep going.
I honestly don’t believe there’s a really compelling reason to try it if you’re happy with your performance as is, but it is an interesting concept in the science of endurance running. I could see where feeling really hungry on a run wouldn’t be fun!
Is it sad to say that I am heading into marathons 4 + 5 this fall and I still am unsure of fueling? Mine has more to do with stomach fears. I am trying to be better this cycle and practicing. When I began doing half marathons I knew nothing and ran them without fueling or even drinking water during so I go used to it at that distance. During NYCM last year though I was eating everything in sight 🙂
I don’t think I have physically hit the wall but oh I’ve hit the wall mentally in each marathon. Usually mile 16 is when the mind goes dark. the thought of still double digit miles at that point for some reason usually sends my brain into a tailspin of thoughts of stopping!
Me too with the mental wall, right around 16 miles. Although with Boston I hit a mental wall earlier on and then got over it. So interesting! I was unsure of fueling too with my own stomach issues, but I seem to have a good mix now with 2 bananas before and powerbar energy blends (the baby food stuff) during. And of course clean paleo leading up to a long run, yes that has been the biggest help! I was the same way with half marathons and still will really only eat a banana and gel packet beforehand and then refuel after.
I have never really bonked and I do some runs fasting, but most of my early runs, I have a protein drink before going out the door. I can dig deeper when I’m fueled. I wanted to say in regards to a previous posting- tomato sauce + sweet potatoes = genius!!! I have never tried it and soooo glad I did;)
I came across the marinara and sweet potatoes by accident but it’s surprisingly good! Agree that the fueled long runs have an extra gear in them for sure, but I like to know I can get by without much since the marathon will deplete me more than any training run.
I’m generally cool with my current fuel strategy, but I know it could be better and I definitely need to revisit it during Dopey training. I totally bonked in my marathon at mile 22. I think that was mostly due to being somewhat under-trained (I had to pack a lot of miles into a short time due to a bout of tendonitis) because I was fueled pretty well through the whole thing. This is a great post and really interesting. I’m going to look into it more. 🙂
I think under-training definitely would make anyone more likely to hit the wall because getting those long runs in even with a solid amount of sugar for fuel is still training you to use fat. It’s nice to know you have a solid fueling strategy though that works, that’s a huge thing for long distance success!
Great tips! I am also fortunate enough that I never bonked or “hit that wall” during a race either. Well up until this point. I hope that it never happens, but you never know how your body will handle a race.
Very true that you just never know what will happen during a race! As prepared as you might be, the body can be a tricky thing and pretty sensitive especially when nerves are high race day. Hopefully it will never happen!
Oooh – I was waiting for this after your comment but didn’t expect it so soon! Awesome post, and so true!
I have only ‘bonked’ once – my first half-marathon, which I have written about. I didn’t taper, and I was still in the midst of weight loss so I didn’t fuel up at all, and held back on the Gu in order to not take more calories. Idiot.
Never again. 🙂
Yeah that combo sounds like a bad race recipe! For my first half I don’t even remember if I tapered, I think I might have just taken the day before off which worked well enough. I used to just have a banana before a race and then nothing until after, but now I like to mix bananas and gels on race day for extra backup. I still haven’t figured out my race day hydration, but that’s another story!
This is really interesting and im bookmarking this–thank you!! I do fasted runs all the time. There are times when I’m so hungry (near the end) and other times where it just helps me keep going and pushing harder bc my stomach isn’t upset by food/bowel movements,
one thing I have noticed lately is that when I get up for a long run, I feel like I could head out the door RIGHT then and be fine. But of course, I’ll eat breakfast like a good girl and then wait for it to digest. Sometimes im more tired AFTER breakfast than before and I’m wondering if i should try a fasted long run?? Definitely some food for thought. And you’re right about the fact that it can make you more
Tired-sometimes running and then going to work exhausts me–lol it doesn’t help that I push it by not eating breakfast til I get to work–this helps the exhaustion!!! Perhaps I will start shoving more coconut water in my face right away bc that sounds delish!!! LOL
I know sometimes for my weekday runs I’ll get caught up in getting my kids ready and not eat anything until 8am when I ran at 5:30, I really prefer to refuel starting right away if I did a harder run. I wouldn’t do fasted long runs every time, but one or two might be a good idea if it feels okay for you. You can bring along fuel in case you really need it!
usually by mile 16 people are depleted on glycogen. But it totally depends on how they fueled the week before, ya know? I also know a lot who are keto adapted and can run on empty. To each their own
So true! I find the people who are keto adapted to be really interesting! I don’t think that’s for me, I am somewhere in the middle since I eat paleo but still include a decent amount of carbs. Psychologically I feel like I need extra carbs to back me up!
Great post, very informative. I have experienced the bonk. It was not pleasant. I admittedly need to get better at fueling.
We only improve after bad experiences! For the next time around you’ll have a better idea of how to train, fuel, and have a great race 🙂
I definitely bonk after about 2 hours of playing tennis! I like that there is someone else out there who also believes we aren’t exclusively carb OR fat burners… we can be both. We just need to teach our bodies.
Absolutely! Kind of amazing what the body can adapt to 🙂
I’m not a huge runner, and just got back up to 7 miles at a leisurely and comfortable 9:25 on my 65th birthday, as I work to get to doing a half in easily under 2 hours, but I MUST say, this thread has provided the singular source of the most useful information I have ever encountered. Thank you all.