Fight the Bonk! Train to Avoid Glycogen Depletion in Your Fall Marathon

ING New York Marathon is just one of many great fall marathons. It is one of those amazing experience races – don’t go ruining it by bonking! Image via

Marathon season is upon us and we at Salty Running know our readers take their marathon performances seriously! So over the next few weeks, we’ll be featuring articles about how to prepare for your fall marathon. From training tips, to picking a race, to what to wear, we’ll be your go-to source of information for your big fall races!

Our first topic in the series is how to train to prevent bonking. Have you ever bonked? Hmmm. Wait. Maybe you don’t know what bonking is (besides an obnoxiously goofy word). Let me tell you a story.

Last October I lined up for my fifth marathon. I was in the best shape of my life. Three weeks earlier I ran 16 miles averaging 6:47 and felt FAN-f’in-TASTIC. I was so ready. How naive I was. My goal was to average 6:50 for the marathon. I was doing well, running 1:29:30 at the half (averaging 6:51 pace). I was chugging along and then right around that magical two hour mark things got weird. I felt dizzy. I felt heavy. I felt insane. I felt drunk. I felt crampy and nauseous and just bad. I could. not. go. It wasn’t just a matter of needing to slow down either. No, I ran out of gas and basically Ginger’s boyfriend James and Pepper had to tow my sad sorry self to the finish line in 3:11:47. I went from 6:50’s to somewhere over 8:00’s in a matter of moments.

What happened to me?

I’m in good company. In her debut Kayoko Fukushi of Japan famously bonked and still managed to finish. She fell flat on her face twice in the last 200 meters of the race! Her body just shut down. Yeah, bonking sucks!

I wasn’t just tired or over it or not tough enough. There was no mind over matter this time. My body ran out of glycogen. Glycogen is the carbohydrates (sugars) our bodies primarily use to fuel our muscles when we run. Typically, a trained athlete stores enough glycogen in her body to get through 2 hours of harder running. So with no added carbs, most of us would bonk at the 2 hour mark of a marathon.

But I did add carbs! I took two gels prior to bonking (we’ll call this point in the race, Point Bonk). With the extra 200 calories of carbs, I should have made it past the two hour mark, right? Well, not necessarily. You see, when we’re running hard and our bodies aren’t used to fueling on the run we might not be able to digest those carbs. My body might have been too busy keeping my legs moving and my brain from going into overdrive (something I struggle with in the longer races) to metabolize the gels I took. Also, when I returned to my hotel room I noticed the half a bagel and half a Clif Bar sitting on the table. Perhaps part of the problem was that my tank wasn’t full when I hit the starting line.

This isn’t the end of the story though. Let’s use an analogy to cars. Our bodies aren’t like my old VW Jetta. Our bodies are more like a Prius. A Prius’ primary fuel is gas, but it’s back-up fuel is a electricity. For people, the primary fuel is glycogen (sugar, carbs, whatever you want to call it), while our back-up fuel is fat (chub, blubber, whatever you want to call it). Our bodies can burn both glycogen and fat at the same time, an act they almost always do unless we’re running really really fast–like sprinting. What’s cool is that we can train our bodies to burn fat more efficiently, This is key because if we can train our bodies to burn more fat efficiently, there will be more glycogen to burn later in the race. We push off Point Bonk somewhere past the 2 hour mark. And if we can train our bodies to metabolize carbs that we ingest while running too, we can make it all the way to the finish line without running out of gas–without bonking.

2004-2008 Toyota Prius photographed in Bethesd...
Hi, my name is Salty! My engine runs on sugar and fat! Image via Wikipedia.

Although actually experiencing a bonk was kind of neat in that I felt like a living science experiment, I would suggest you do everything in your power to get to the finish line of your fall marathon with a little sugar left in the tank. “But what can I do now to avoid bonking in my fall race? ” you might be asking. I might answer, “Good question!” and then continue with this: based on my experience and research there are three things we can do before the marathon to avoid running out of glycogen and bonking.

1) Train our bodies to burn more fat and to reserve glycogen.

It’s pretty simple to teach your body to burn the chub rather than the fuel. You run when you’re glycogen tank isn’t full. There are a couple of easy ways to do this. Run long without taking in carbs, run doubles without replenishing your glycogen stores fully in between runs, or back-to-back longer runs (2 runs of 90 – 120 minutes on two consecutive days). The latter two options are for advanced runners only. The easiest and best option for most of us is to do several long runs without taking in sugar (gels, sports drinks, etc.)

2) Learn how many carbs to take in during the race and practice taking them to make sure your body can metabolize them.

It’s really easy to teach your body to metabolize sugar. Do some long runs with some marathon-paced running during which you do take in a gel or two and\or sports drink.

3) Make sure your glycogen stores are full before you hit the starting line.

This is the easiest of all: eat the entire bagel and the Clif Bar before the race! Also, the days before the marathon are no time to diet. Even though you’ll be tapering and not burning as many calories, you still need to eat lots of carbs. We’ll help you out with a pre-marathon diet in the weeks to come.

Simple Bonk-Prevention Marathon Workouts

Ok. So now you know that you need to train your body to burn fat and to metabolize sugars on the run, here are some actual workouts you can incorporate into your training plan to bonk-proof yourself for race day.

Sometimes you need to leave this stuff at home on your long run days. Image via

Fat-Burning: It will take several weeks to work the fat-burning system. When you run at an easy pace you don’t burn through your glycogen as quickly as you do when running marathon pace, so you can actually do your long runs without carbs. It might not be pretty, but it’s an important lesson to teach your body. Here is an example of a three-week progression of long runs that will train your body to use fat to fuel you on the run:

  • During 1 week run 2.5 hours easy without ingesting carbs during the run.
  • During week 2  run a total of 2.5 hours without ingesting carbs and run easy until you have 2:10. From there run marathon pace for the last 20 minutes of the run.
  • During week 3 do the same 2.5 hour run without ingesting carbs and up the marathon-paced portion to 30 minutes.

Sugar Metabolizing: This system doesn’t take as long to train as the fat-burning system. One or two workouts will do, especially if you already take energy gels or drink gatorade while running regularly. Here is a sample workout that will train your body to metabolize sugar at marathon pace:

  • Run a total of 20 miles. Run the first 10 easy,  then run 8 at goal marathon pace taking a gel 2 miles into the marathon paced portion. Run 2 miles easy to cool-down.


If you’d like to read more about bonking, fat-burning, or glycogen stores check out these links:


Have you ever bonked? Do you always take in carbs during your long runs? Think you might try to train yourself to burn fat more efficiently by not taking in a gel or sports drink during some of your long runs this training cycle?

Salty Running boss and mother of 3 little ones with PRs of 3:10:15 (26.2), 1:25:59 (13.1) and 18:15 (5k). I love to write about running culture, mental training, and fitting in a serious running habit with the rest of a busy life.

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  1. Hi Salty,

    Thanks for the link to my article on bonking. I am glad you enjoyed and found it helpful. Nice work with your article and the details. Very helpful and great information. Keep up the great work!

    1. I cannot believe that this is the second time this has happened in two months. I bonked the first mile! I am 58 and run 6 miles every morning at 5 a.m. seven days a week. From the recent readings I can only guess there are two things I need to do (most articles are geared towards the marathon but this is a simple 6 mile run!) I weight 123 lbs @ 5’3″ and I am vegetarian. I eat a lot of raw fruit and cooked vegetables. I can only guess I am not ingesting enough calories along with the calories I am ingesting not containing enough carbohydrates. I have been running since 7th grade and have never experienced this before. It is concerning! Any further advice? Please email @ as I may forget to check your website.


  2. Hi Salty,

    This makes so much sense! I am a new runner, 60 years old, and have a lot to learn. Lately I’ve noticed that my body feels heavy and tired when I run. Evening before last, I weakened and ate two brownies at my son’s house – the first break in my diet for more than two months. Yesterday morning I felt so energized that I decided to run eight miles instead of the three I had planned, and felt great! My motivation for dieting is wanting to carry less weight on my legs when running, but now it’s clear that the day before the run is not the best time to cut back. Of course, I don’t plan to binge on brownies again, but there are plenty of good choices out there. Thanks also for the tip on cutting out carbs during my runs. I like the sound of “burning chub.”

  3. Can I first just say that I am super pumped for fall marathon posts!! Question- for someone like me who wants to achieve a 3:30 marathon, do you still recommend a long run of 2.5 hours without gels or carbs? For me, that’s about 18 miles. I don’t know that I could do that without seriously hallucinating. I can definitely do 10-12 miles, but even before those long runs, I have something to eat to put some gas in the tank. Would this be a suggestion for someone who is looking for a sub 3 marathon? I do very well with taking in my blocks during a long run, so I’m good on that front. I have only run 2 marathons, so I can’t really talk from experience. My first one was just to finish & the 2nd one the wheels fell off the cart around mile 22, but I know that was due to the 80-85 degree temps & blazing sun. I was busting out an 8 minute mile or less for 21 miles & felt great!

    1. YES! Try the 3 18’s without carbs. It might be tough, but you can do it and you’ll be better for it! This will help you in Akron, especially with the hills burning up glycogen late in the race. You can eat something before the run, just don’t take anything in on the run. I’ve run 22 miles with no gels or drinks of any kind and survived and back then NEVER had a bonk problem. I took in gels or sports drinks during all my long runs last year and no fat-burning workouts per se and I think that contributed to my bonk. Also, as I was writing this post it occurred to me that the fact that I was still nursing might have inhibited my bodies willingness to burn fat and that might have had something to do with it too!

  4. Unfortunately I can raise my hand for the question “have you ever bonked.” It is not good any way you look at it because it hurts and it is mentally hard to process the fact that you botched your race after months of training. I personally think there are 2 keys to avoiding the bonk: (1) carbo-load correctly the week before the race. This is so important. Not only is it key not to diet, but what you put in your body the week/days before the race is pretty important; and (2) carb up the morning of the race and take in as much sports drink / gel as you can early on in the race. Many of us wait to long in the race to start taking gels/etc. and we spread them out too far. But we really need to take in as much as we can handle early on because as we hit those later miles our bodies are working in overdrive and it is much harder to process and absorb the gels. My current coach gave me this tip #2 before my last race. I did it and was amazed at how much better I felt throughout the race and I never came close to bonking.

    1. I could have used that tip last fall! I could have died when I saw that half eaten breakfast sitting there when I walked in my room. UGH. Live and learn 🙂

  5. Love this. I think we have all learned the hard way that nutrition is so key for marathon preparation and execution. Thanks for the advice about the workouts. I will be using them!

  6. Never bonked. I assume it is because of my secret donut stash of extra carbs 😉 But I do agree with all these training benefits. my rule of thumb is on any easy long run i try to avoid intake, on any long run with a harder effort i add fuel.

    1. I never had either before kids. As I was researching and writing this post it made me really think that my body cut back on the fat burning since I was still nursing. I wonder if that run in Chardon when I died was bonking\hypoclycemia and not dehydration because the symptoms were very similar to that! Yet another reason I won’t be racing a marathon in the near future!

  7. Great post! I was talking to a friend about this during our run this morning. The science totally makes sense, but I was telling her that my snacks, as I call them, are part of my routine. I realize they are basically a crutch, but it’s a little scary thinking about heading out on my 15 miler tomorrow without nutrition! I definitely want to try this at some point, but it’s just hard to mentally make that leap.

    1. You can do it! I think runners these days (as if I’ve been running longer than the almost-8 years I have been!) rely WAY too much on energy gels and such. Their necessity is 3 parts marketing and 1 part in our heads. They are certainly a useful tool for certain points in training and racing, but they aren’t the necessity for every run that some think they are. At an easy pace you can run for hours without replenishing your glycogen stores. Sure, you might get tired but that’s kinda the point! If you ditch ’em this weekend definitely let us know how it goes!!!!

      1. Hi Salty, I have to put my 2 cents in here, I am training for my first Marathon and I have been running religiously for 3 months, longest run was 12 miles in which I did not have any issues. Usually I hold a bottle of water during my runs and I would have a sip every mile or so, usually the bottle last me for about 9 miles. Last Saturday was a long run of 15 miles, I did it at 730AM, the only breakfast was a yogurt and a glass of water. Everything went fine until mile 12, I was averaging 8:40/mile, then immediately I went to 11min/mile, so basically I could not lift my legs and started to limp. I was a bit worried because I thought my body was telling me to stop and I did not want to get injured, my breathing was fine and my will to continue was still good. I limped for another mile and then I stopped since I thought it was ridiculous to continue. So you are giving advice to run without fuel in the morning, but isn’t this action going to repeat the results I had? this saturday I am going to attempt another 15 mile, I might eat a bit more for breakfast maybe 2 yougurts and see how it goes ….

        1. Maybe try something with more carbs in the morning like toast or a banana to go with the yogurt. The other thing is that you might be going too fast. Have you raced recently? What distance and what was your time? What’s your goal pace for the marathon? Do you take gels and such during your runs usually?

          1. Hi Salty, thanks for the quick reply, all my races are 5K and 10K and I average less than 8 for 5K and 8.5 for 10K, my goal for the marathon is to finish under 5, my stretch goal to finish at 4:30. never took gels or gatorade, just water. my previous 12 mile run was at 9 min pace, no issues, one thing I noticed is that I can’t go slow or fast, my body get into a rythim after the first mile, and it looks like it is about 8:40 – 910. I used to train with HRM, but it became too tight on my check and I wasn’t getting the benefits I need from it, so now I just go with what my body tells me. This WE I am doing 16, hopefully, I might add a toast or a PBJ sandwish to my yogurt and see how it goes …

          2. Sounds like you ran way too fast so you were essentially racing your long run. If you’re running them at the proper pace and you’re a healthy person you shouldn’t need too much in the way of carbs to get through them. You might feel uncomfortable later in the run, but that’s to be expected. I’d slow it down closer to 9:30-10:00 and you should be able to get through it. All this in mind, make sure you practice your marathon fueling on a couple of long runs before your goal race.

  8. I’m a big believer in training in a fasted state on a regular basis, and now think it’s one of the most compelling reasons to go out predawn (or, at least, pre-breakfast). While that’s always been my training approach, I think I reached a breakthrough last year by doing a gazillion mid-week medium long runs (90-120 minutes) without breakfast, in addition to the usual weekend long runs. Last fall’s Towpath was the first race where I took zero gels, though I may well have gotten sufficient (or, at least as much as can be processed) carbs via the ample Gatorade supplies on the course. And I’m glad you found Jeff’s site as well, I’m not sure there is a better source (and you need to watch his articles on competitor) these days for hard-hitting training insights.
    I assume you’ll be going into the art of the carbo-load at some point too, as there is more to this than just eating a lot the day before the race.

  9. I’ve been running now a little over a year and still learning what works for me. So let me get this straight.. Load up on carbs few days prior. Eating breakfast is ok, no gels during the race.. Is Gatorade ok?

    It’s funny because a veteran runner once told me, running has been around a long time. Gels didn’t exist 20 years ago. What do you think racers did?

    Anyhow, I almost passed out at the end of a half marathon. I didn’t take any gels before or during. Not sure what went wrong. Maybe waited too long to eat after I was done racing. But I have a triatholon in August and not sure how to fuel for it.

  10. Thanks for the great info. Just finished a half (1:49) and want to run a full. Have plenty of time to train. Really want to train correctly. I have never really run a long run “easy” enough to properly let my body burn fat. My marathon goal is 4 hrs. Any more training advice?


  11. I just ran my first marathon last week and was shocked when i bonked at mile 26 (yes, you read that right). Technically, from mile 23 on, i basically wanted to die. I was planning on a 3:40/45 finish and was solid up until 23. At mile 26 my right leg literally stopped working and i was unable to stand up on my own. I ended up getting help to the finish but one of the people helping me was just a bystander which resulted in a DQ for me. Also, the medics picked me up 10 feet from the finish line so they DQ’d me as well. I am still working this out in my head but am determined to complete another marathon in October. I am pretty sure i just ran out of gas but before i run another marathon, i need to figure out what to to do different. I think i need add’l nutrition to get me past 20 (which i can run comfortably). Any suggestions on how to figure out how much nutrition you should ingest while running? It’s hard b/c you really don’t train much past the 20 mile mark which seems to be my issue. My weekday runs are all fasted runs so my body does know how to run on my reserves. During this race, i ate 3 GU’s (one every 7 miles) but maybe i needed a LOT more than that! Not sure how to tell. Any advice is helpful b/c this CANNOT happen to me again!

  12. Just found this while searching the internet for “WHY DID I HIT THE WALL?!”

    I hit the wall hard in my first marathon and I thought it was something that was only for other people. In other words, it was not something I expected would happen and there’s no way to know what the wall will feel like until you’re up against it and MAN does the wall steal your race from you. I had pretty much the same experience as you (only my miles went from 8:20’s to 10:30s–just a tad slower 😉 and it was so disappointing!

    Definitely bookmarking this article for my next marathon. Can’t wait to do it again. Thank’s for this !

  13. Great article…planning for my first marathon in 18 months so very handy.

    Tried a gel in training for my first half marathon this year and couldn’t do it…have heard that baby food puches work just as well. Any thoughts?