How to Fuel During Endurance Events


Some of the most frequent and consistent questions we get at First Endurance have to do with how and what to use for fuel during exercise.  If you have any questions or comments, we’d love to hear from you.  Just comment below and we’ll make sure to get back to you right away.

Rocket Fuel for your Body- Glucose is always circulating in your blood and is the ‘rocket fuel’ for fast paced workouts or races.   In fact, without glucose you are going nowhere fast.   Your body can produce glucose in two different ways.  The first, which also is the most efficient, is by utilizing the glycogen that’s found in your muscles and liver.   This is a fairly fast and efficient method that can deliver a quick supply of glucose to fuel your workout.  The downside is that we only have a couple hours worth of this stored glycogen at best.
The alternative option is for your body to convert non-carbohydrate sources like protein and fat into glucose.  Even though we have days and days of fuel stored as protein and fat in our body, this option can be quite inefficient.   The pace at which you are exercising will determine what fuel your body uses.  To a lesser degree your body’s own efficiency also determines what fuel is used. 

Avoid ‘hitting the wall’- Your intensity determines whether your body utilizes fat or carbohydrates to fuel your workout.   For an all-out sprint, your body will use glucose- the most efficient fuel to drive the working muscles.    At a slower pace, or in a situation where you have burned your glycogen, your body will breakdown stored fat for fuel.  Remember: your body has to convert fat to usable glucose in order to fuel the workout.    It’s this inefficiency or slow rate at which your body converts the fuel source that causes you, or forces you, to only use this fuel during slow paced workouts.     The dreaded ‘bonk’ is one of those times where you have run out of stored glycogen and you get the sensation of having no energy and being in an extreme state of exhaustion.

Tip: Consuming fast absorbing carbohydrates spares glycogen because these carbohydrates get used instead of your stored glycogen.  In this manner performance remains high whether you are sprinting or going very, very long. 

Teach Your Body a New Trick- The good news is you can condition your body to convert fat to glucose more efficiently.  Not only will this increase your ability to go longer, it will reduce your need to take on additional calories during training and racing. This process uses a systemic method of training long distances on very little carbohydrates in order to train your body to burn fat more efficiently.  This is the premise behind what is called ‘substrate utilization’ or ‘substrate training’ for long distance athletes. This is a significant benefit on race day because you’ll be more efficient at burning fat and sparing glycogen.  This type of conditioning also allows you to consume fewer calories per hour, which often results in a decreased risk of gastric distress.

Tip:  It takes many months to adapt to lower carbohydrate training and racing.  Use a well designed plan that uses lower carbohydrates instead of training with water only.   For fast paced workouts fuel fully. This assures you get great recovery AND substrate training. 

Fueling in Different Conditions:  We’re talking primarily about temperature when we discuss fueling practices in different conditions.   When it’s hot, your body expends a large amount of energy trying to cool itself by dissipating heat.  It does this by circulating more blood to the skin surface so you sweat more.  This leaves less blood to aid digestion AND you require more fluids to keep you sweating at a high rate.

This high sweat rate is a sign of efficient cooling but does require fluids and electrolytes in order to sustain workouts over many hours.

In cooler and even cold conditions where your body does not sweat, you do not need to consume high rates of fluids, but you still need the calories.   Adjust your fluids and electrolytes to match the ambient temperature.

Tip:  If its hot and you will sweat make sure the concentration of your calories is no more than 100 calories to 12oz fluid.   In cold conditions you can double this concentration to 200 calories to 12oz fluid.

Be careful what you eat:  Ingesting slow absorbing fuels like proteins, nuts, fats, foods with fiber and other solid foods during workouts can cause gastric distress as well a premature “bonk.”   Slow absorbing fuels get stuck in the gut, which means your body can’t readily utilize them.   If your body is burning stored glycogen as it waits for those slow nutrients to get absorbed, you’re reducing your 2 hour fuel tank and increasing your chances of ‘bonking.’  To reduce the chances of ‘bonking’ or gastric distress eliminate all slow absorbing nutrients from your fuel plan.

Tip:  An empty stomach can absorb your drink fast and fully.  Keep your stomach empty by only consuming fast absorbing drinks instead of slow solid foods.  In long distance racing, hunger is a sign of an empty stomach its NOT a sign that you are bonking.  Stay hungry my friends. 



How to Use EFS, EFS Liquid Shot and EFSPro for Any Distance:

Whether you are out for an intense high paced 45-minute workout, or about to embark on your 100-mile ultra distance run, EFS products are designed to fuel your workout at any distance.  The below recommendations are loosely based on a 150lb athlete.   In order to properly manage your nutrition its important to first ask these questions.

1) How much will I sweat?  IE: How hot will it be?

2) How long will I go?

3) How fast do I plan to train/race?


New EFS Drink FamilyEFS drink: Designed to be used at an 8% solution (100 calories per 12oz).  Delivers high levels of 5 electrolytes.


efs-ls-ssEFS Liquid Shot:  Designed to be used for cold weather training and racing or as supplemental fuel.  Delivers high calories and low electrolytes.


pro-familyEFSPro drink:  Designed to be used at varying concentrations (80/100/120 calories per 12oz).  Additional nutrient technology helps shuttle electrolytes into working muscles and increases absorption rates in the most extreme conditions.


< 2 hours COOL/COLD conditions:  Because high levels of electrolytes are not critical EFS liquid shot works well in this situation.  Consume 100 calories EFS per hour at a solution between 10%-16%.     This means 100 calories for every 6-10 ounces fluid.    One ounce of EFS LS is 100 calories.  Pour up to 4 ounces in a water bottle and top off with water.

< 2 hours HOT conditions:  Change to an 8% maximum solution.  This means 100 calories to 12 ounces.  For most EFS drink will work great.   If you are prone to cramping or have difficulty absorbing drinks when the pace is high consider EFSPro.

2-5 hours cool/cold conditions:  Consume 200 calories EFS per hour at a solution between 10% and 16%.   This means 100 calories for every 6-10 ounces fluid.  Electrolytes are still not critical, however due to the longer workout a mix of EFS drink and EFS liquid shot works great in this situation.

2-5 hours HOT conditions:  Change to a 8% maximum solution.  This means 100 calories to 12 ounces.  For most EFS drink will work great.   If you are prone to cramping or have difficulty absorbing drinks when the pace is high consider EFSPro.  You can supplement 50% or less of your calories from EFS LS.

5+ hours COOL/COLD conditions:  Consume 250-300 calories EFS per hour at a solution between 10% and 16%.  This means 100 calories for every 6-10 ounces fluid.   For very long distances  your body will balance the use of stored fat, stored glycogen and orally administered calories to fuel the workout.   Consuming only fast absorbing fuels assures that you deliver glucose consistently to the blood, which can help spare glycogen so you don’t bonk.  A mix of EFS drink and EFS liquid shot works great in this situation.  Your PACE will determine how many calories you need.  If the pace is slow, less calories are needed.  If the pace is at threshold you will need more calories.

5+ hours HOT conditions:  Change to an 8% maximum solution.  This means 100 calories to 12 ounces.    At subthreshold pace EFS drink will suffice for most individuals.   At a fast threshold pace, where the body needs high electrolytes and sufficient calories consider using EFSPro as your primary calories.    The longer and the hotter the conditions the more athletes should rely on EFSPro as their primary fuel.   EFS LS can be used as supplemental calories, however this should be limited based on distance and pace.

Tip:  In a race where temperatures will vary during the day so should your nutrition.  Plan your nutrition to match the ambient temperature so in cold conditions you have less fluids and electrolytes and in hot conditions you have more fluids and electrolytes.

46 responses to “How to Fuel During Endurance Events”

  1. esjaime44 says:

    If we are training with minimal calories during training, do we also race with minimal calories if the race is longer than a 50K?  Are you suggesting to avoid all solid food in races that last 24 hrs and beyond?

    • Robert Kunz says:

      @esjaime44 Scott, running and especially running long distances in the heat creates the most challenging fueling strategy.    The goal of training with low calories is to teach the body to use fat efficiently so on race day your body does not need to ingest as many carbohydrates.   On race-day however you should still try and ingest as many fast absorbing calories as you can to assure you do not run through your glycogen stores.   This means that with proper and well designed low carbohydrate training, come race day you might be able to consume 50 or even 100 carbohydrates calories less per hour than if you did not adapt your body to efficient fat burning.    So maybe you consume 250 calories per hour instead of 300 or 350 calories per hour and still have the energy to go the distance.  Because you are down to fewer calories per hour it lessens the chance of gastric distress.   
      24 hour races and beyond are a great challenge nutritionally.   We do understand that solid foods do play a role here though an athlete must be very smart and systemic about introducing these solid foods.  We suggest the vast majority of your calories come from liquid. And yes you can go all 24 hours on liquid alone.    You can systemically ingest solid foods, however we urge you to spread it out and do it in small quantities.   You can also consider more solid foods during your night running when temperatures are low because you can combat the nutrient density of solid foods with appropriate water (10-16%) solution.  IE: In the heat of the day a 200 calorie bar would require 24 ounces fluid to digest whereas in the cool of the night you might get away with 12-16oz fluid to digest the bar.

  2. esjaime44 says:

    One additional question:
    I run once a day and have been training with minimal to no calories on my longer runs once per week (2-2.5 hrs).  In order to achieve this I run in the morning while my body is depleted of glycogen, how long should I get to (hrs) and how many weeks to create the metabolic response to burn fat?
    Thank you for the article – perfect timing!

    • Robert Kunz says:

      @esjaime44 Good question.  You are already getting a metabolic response to burn fat.  The change is not an on-off switch.  Its more of a slight shift that allows you to burn your fat a bit more efficiently.  I do urge you to be careful forcing the shift as the downside of low glycogen is poor recovery and high stress.   Take the time to read our article on how to do this properly so you can maximize performance AND get the metabolic shift you are looking for.

  3. Ultrarunninfool says:

    Is EFS an all in one sports drink? Being an ultra runner and using a well known product currently, it is not an all in one. Looking for something that is like an all in one. Do I need to have gels, salt tabs or food at aid stations with EFS? I’m 6’2″ 195 lbs and I run all distances of ultras. I live in NC and the humidity in the summer can be pretty high so I sweat alot. Winter is pretty cool, in the 30-50 degree range. I train 70-80 miles a week not including cross training. So if I run a 50 mile ultra can I just use EFS without worrying about carring anything else with me? Thank you!

    • Robert Kunz says:

      @Ultrarunninfool EFS drinks are an all in one product, however all humans are not created equally so some modification may be necessary for some individuals.   For the vast majority EFS can fuel your entire Ultra run.    Its best to start using EFS in your training and experiment as you go longer and longer.   Though our EFS liquid shot flasks are not necessary, they do offer a very convenient way to carry a lot of calories.  The liquid shots are a nice complement to the EFS drink.

      • Ultrarunninfool says:

        @Robert Kunz Thank you Robert! I will be ordering the EFS drink mix and EFS gel shots. How do I mix the drink with the gels during training and running my ultras? Don’t want to over do it. Should I mix the drink according to my weight and weather conditions? Is there another product that you have that you would recommend for me? Trying to keep cost down but would like to make sure I get the right products. Thanks for your help and sorry for all the questions, just want to make sure I order the right stuff seeing that I will be spending a good amount of money.

        • esjaime44 says:

          @Ultrarunninfool  @Robert  If it helps I’ll tell you what I do.  I’ve been using FE products for the better part of 8 years so I have experimented with a lot of different products and concentrations.  I run trail ultras and what I’ve found best is the following:
          For days when the weather is below 70 degrees I only use EFS liquid shot.  I dilute 1/2 flask (200 calories) into a 20 oz bottle bottle of water.  This way I am getting water, calories, and electrolytes.  On race day, I will finish this bottle in about 1 hour and 45 minutes.  For a 50 mile race I will typically go through 4 of these bottles.  
          For days when the weather is above 70 degrees and more humid I will add one 20 oz bottle of EFS (grape) to the above regimin.  Usually I will go through this bottle in 2 hrs, along side the EFS LS bottle.  The grape tends to be less sweet than the fruit punch.  
          Hope that helps

        • Ultrarunninfool says:

          @esjaime44 @Robert Thanks Scott! So the EFS shots is not a gel? You can mix it with water? Didn’t know that. Sorry I’m just new to the product. So can I mix the EFS drink and then sip the EFS gel? What is the difference between the two (drink/gel)? Kind of confused with the 2 products and how to use them together. I will be ordering the 2 products and seeing how ill mix and match the 2. Any of the other products you recommend? I’m an avid trail and ultra runner. Being 6’2 195 lbs I require lots of calories. Thanks for your help.

        • esjaime44 says:

          @Ultrarunninfool    @Robert  EFS Liquid shot is “gel like” although it does not have any binding agents.  What this means is that it is not as viscous as most gels, it’s almost the consistency of syrup.  It mixes really well with water.  I dilute it because it tends to be rich.  The liquid shot has the calories you need, EFS will only provide a minimal amount of calories and will not be enough to last an ultra.

        • Ultrarunninfool says:

          @esjaime44 @Robert ok so the EFS drink is for calories but mostly used for the electrolytes and the aminos and the gels are for the calories? Is that correct? I guess I’ll have to get both products and try and figure out what works for me. If I have any questions I’ll write to this post. How do you use both the products for a 50 mile and above ultra? I use about 300-350 calories an hour.

        • esjaime44 says:

          @Ultrarunninfool    @Robert  I don’t use the EFS drink for calories, I use if for when conditions are hot.  FE products have the most electrolyte content of any other product.  I use the Liquid Shot for calories and since it has electrolytes in it, it provides enough for my needs most of the time.  Anything above 50 miles I will also eat potatoes, soup, and anything else that will go down.  I have tried to do LS for the entire 100 mile journey but it just gets to be too much and I need more variety.

        • Ultrarunninfool says:

          @esjaime44 @Robert ok so just using liquid shots up to the 50 mile ultra is enough of the electrolytes and calories I will need in cooler weather? And for warmer weather regardless of the distance, supplement the EFS energy drink for more of what I need. Again sorry for all the questions and thank you so much for answering them. I’ve had some bad luck with other products.

        • esjaime44 says:

          @Ultrarunninfool    @Robert  Yes.  But as Robert says, train with both first.  If you do both LS and EFS drink, that is a lot of electrolytes so you need to train your body to accept them.  I have found that I don’t need that much so everything I do with FE is diluted.  And that means only one scoop of EFS drink to 20 oz of water

        • Robert Kunz says:

          @Ultrarunninfool  @esjaime44  @Robert   In HOT weather you will need the high electrolyte content of the drink.  In cooler climates, the electrolyte content is not as critical and hence the liquid shot works well.   In very long distance racing where the weather can both be cool and hot a strategic mix of the two works well.    
          In the coming week we will be posting the nutrition plans from our sponsored pro Ultra runners.   Everyone uses these products a bit differently so with these plans you can view modifications in plans and decide for yourself what makes the most sense for you.

        • Ultrarunninfool says:

          @esjaime44 @Robert Awesome! Last question. How much plain water are you drinking during an hour of training/racing while drinking EFS and/or LS? Thanks again! Looking forward to using EF products.

        • Ultrarunninfool says:

          @Robert Kunz @esjaime44 @Robert that will be great! How much plain H20 will need to be taking in when using EFS drink and liquid shots? Or is it enough hydration while using the EFS drink and liquid shot that are diluted?

        • esjaime44 says:

          @Ultrarunninfool    @Robert  I don’t use any additional plain water in training but in races I make good practice to take a dixie cup full at each aid station

        • Robert Kunz says:

          @Ultrarunninfool  @Robert  @esjaime44  @Robert  Start by following the recommendations in the article so you get the right solution percentage during different temperatures.  From there you can experiment a bit to see what your individual tolerances are.

        • Ultrarunninfool says:

          @Robert Kunz @Robert @esjaime44 Robert- thank you! I’m going to put my order in tomorrow. How much EFS sports drink should I order and what flavor do you recommend? How much of the liquid shot should I order and what flavor do you recommend on that as well? Is there anything else I should pair up with these 2 products that you think will help. Thanks again! Richard

        • Robert Kunz says:

          @Ultrarunninfool    @Robert  @esjaime44  Flavor is your preference.   Our best selling EFS is lemon lime and fruit punch though these are the sweetest.  My preference is for less sweet so I go with orange or grape.   For the liquid shot vanilla sells best yet most say kona mocha tastes the best.    How much you order is also entirely up to you.  
          The First Endurance products are a complete and concise ‘system’ of products designed to work together.   So ultimately we recommend all the products, however you need to decide how much you need and want to get out of your nutritional plan.

  4. Kiwi Chris says:

    Kiwi Chris

  5. Kiwi Chris says:

    Hi Robert,
    I have experienced this gut problem of bonking in my A race which is a endurance cycle over some mountain passes. Last year I used EFS in combination with the gel. But got it wrong half way through by eating too much gel.
    The race will be circa 9 hours – last year by body weight was 187 pounds, avg wattage 233w for 9hrs 19min. And temp was about 72deg F. On my bike I have have 2 x 24 ounce bottles. My questions are three . As this is a mountain cycle race temps can very it can be very cold and very hot. On a cold day temp will be avg 59f and on a hot day can be up to 86 deg f. What would you suggest as a furling strategy for both days. I use multi vit and optygen and will take this in training and before the race. How would you suggest I pre fuel on the morning of the race? Until now I have had small breakfast toast n jam plus one 18oz of ultragen. Note with the EFS gels I have had some problems digesting during race in combination with EFS. I can pick up bottle on the way through the race from support – could I use ultragen as a calorie supplement to top up on hot days?
    Sorry for all the questions – love the nutrition!

    • Robert Kunz says:

      @Kiwi Chris  Chris,  Its perfectly acceptable and recommended that you do change your solution percentage as the temperature changes.   Even within the day if you start your ride at very cool temps like 59 degrees you should be well served consuming 100 calories to 6oz water.   As the day heats up change your solution to 100 calories to 12oz fluid.  Carrying flasks or making high calorie water bottles works great as long as you have the appropriate amount of water to grab at aid stations.  IF you feel the slightest stomach distress then immediately go to water for 30 minutes and start cutting your solution so its closer to the 8% (100 calories to 12oz)

  6. Thanks for informative post. I am pleased sure this post has helped me save many hours of browsing other similar posts just to find what I was looking for. I bookmarked this blog a while ago because of the useful content and I am never being disappointed. Keep up the good work Just I want to say: Thank you!

  7. Rcraig84 says:

    For upcoming IM Cabo the weather could be cool or hot. I won’t really know until race week. I’ve been mixing 3 scoops EFS drink and 1 flask of liquid shot in a 24oz bottle.(688 cal) I planned to carry 2 of these to give me about 250cal/hour over the 5:15-5:30 bike. Should I cut down on the calories in the bottle and just carry an additional LS flask? I will also be drinking course water.

    • Robert Kunz says:

      @Rcraig84 Calorie consumption should not change based on the weather.  What changes can change is the total amount of fluid you consume.   Your plan to put 688 calories 24oz bottle is perfectly fine as long as you calculate the appropriate amount of additional water you consume.  If its HOT consume 12oz for every 100 calories.  If its cool you can cut this down to 6oz to every 100 calories.

  8. jake says:


    This is the best forum, seriously the guest questions and info provided is amazing. My issue is that as a “clydesdale” (6’1″ 240lbs) i always have issues fueling for distance – i will take your advice and read the article but anything you could share for us big’ens would be appreciated. I am currently training for the 2014 Big Bend Ultra and reside in north central Texas where heat is always an issue – i have completed several 25k trail runs but in 3 of those i felt that “bonk” and fought my way to the finish line. Looking forward to your product

    • Robert Kunz says:

      Start by focusing strictly on carbs, water and electrolytes. All other nutrients are not necessary and can complicate your fueling plan and put stress on your digestive system. Determine what your upper level of calories per hour is by testing this on long runs. Also keep a log of your concentration percentage so you know what is appropriate for you.

      -Know that many ‘Bonks’ occur not because one did not consume enough calories, but because the calories they consumed were too slow to absorb. If your plan implements only fast absorbing calories you increase your chances of success.

  9. Just few comments about fueling for colder races (of course depending on your taste buds)
    From my experience of 20 years of racing (50+IM races), and working with many amateur athletes of different levels – I learned that lots of people do have the tendency of not drinking as much, and calories from only sport drinks are lot harder to take it. Athletes are colder, they don’t sweat as much, so they think they don’t need to (or just don’t have the urge of) hydrating as much.
    So after few different tests, and approved by few of my athletes – this is one of the better formulas that I came with – of course try to consume as much water as you can, but this could give an idea on the calories side:
    1/2 IM races
    1 bottle (plain water bottle) of 6 servings of Liquid shots + 2-4 shots of espresso + little water
    1 bottle of EFS + Pre-race

    Full IM races
    1 bottle (bigger 24oz water bottle) of 10-12 serving of Liquid shorts + 2+ shots of espresso and little bit of water if space
    2 bottles of EFS + Pre-rece

    (the reason for espresso besides the taste for coffee loves, and water = makes the Liquid shots runnier under colder temps, and the extra few oz of water)

    • Forgot to mention – the nutrition plan for for the bike portion of each race.

      Running portion:
      1/2 IM
      take a Liquid Flask (400 cal), and am able to drink mostly water. If I feel need that extra cal. take a sip of Cola.

      Full IM
      1-1.5 scoops of Ultragen in the transition
      1 gel flask for the first loop or 13mi section
      again 1-1.5 scoops of Ultragen in the special needs bag
      1 gel flask for the second 13mi
      – drinking as much water as I can

  10. Spencer Cearnal says:

    Has anyone used the “PreRace” formula later in the day with any results? The “PreRace” I am using before training and racing it keeps me very focused and amped up but not jittery at all. Wondering if having some later in the event would be beneficial or not? IronMan time of 9:30-45 so maybe ~5-7 hours take in more “PreRace”? THOUGHTS?

    • Robert Kunz says:

      PreRace used on the 2nd half of the bike or at T2 is what we recommend based on input from many Ironman athletes. Its a perfect way to set up a strong marathon.

  11. Blakestar85 says:

    Thanks for the great info everyone, has been very interesting to read. Hoping to hear some thoughts on my first experience with FE products.
    I ran a little over 20kms during which I drank 40oz of 2 scoop EFS. I also diluted 200cal LS with 20oz water, of which I drank about half. It was quite a hot run, probably 80deg f. It was just under 30 deg Celsius. Anyway I felt fine the first hour, but really struggled the 2nd hour. I felt a lot like I just wanted water and felt a bit sick from the sweetness of the 2 drinks . I had planned on a 4hr / 40 km run yet consumed all of the EFS I had planned for the 4hr run in 2 hrs. I didn’t feel well or energised enough to continue in the conditions and pulled the pin just after 2 hrs. It was only a training run so was going to over do it. I don’t normally have a problem with the distance or the heat, so I really think I got it wrong with the fuel.
    My question is, did I over do it with the EFS and LS? Should I have taken on plain water also in the heat? Did I get the mix right for the conditions of the EFS? And other thoughts?

    Thanks all

    • Robert Kunz says:

      This may seem odd, however I suggest you do the exact same run with the exact same mix. What you did in the first run looks appropriate and should not cause any adverse issues. Because of this, I tend to believe you simply had one of those days where the body does not want to go. We all get them. As a scientist, I now have one data point (your first run) and cannot make a true correlation with only one data point. Please try again and let us know how it goes.

      • Blakestar85 says:

        Thanks Robert. I ended up completing the run a few weeks later with the same formula mix. I did also consume around 40oz of water during the 4 hours. I didn’t feel great again, but better than last time. I think you were right in that I just wasn’t having a good day, coupled with me getting used to the EFS and the LS. I have had a number of shorter runs since using only LS for fuel with excellent performance results. This is in training for a race tomorrow. Looking forward to using First endursnce products for the first time in a race. Appreciate you taking the time to provide some advice.

  12. RunnerGirl says:

    I’m interested in trying EFS but am a little confused on how to use it. I’m getting ready to run my 5th marathon in April, 4 out of 4 marathons I’ve had severe cramping issues in my calves, however I seem to have a sensativity to the sodium/salt as well as by the time I finish a race my hands are so swollen they look like they belong on a 300 lb person. My past finish times have been around the 4:30 mark but that’s with have to walk/run the last 5-6 miles due to the cramping. My goal time is 3:55. I carry a camel pak on all my runs, I am a thirty runner. Right now I am running with efuel but I have also tried Accererade and a custom blend from Infinit, as well as several others. I carry my camel during races. I’m not sure if I need the drink mix and the shot, or just the shot, or just the drink. I read too that plain water was not necessary but I’ve always been told you need plain water to get optimal results from gels. I’m also kind of confused on knowing how much to use each run, I see the breakdown above in How to Use in Any Distance, so you have to adjust the formula every run, right now I use the same for all my runs. My other issue is on race day, if I use the drink mix and need to refill my camel pak 1/2 way through that means I have to stop at a water station, try to estimate on water/mix ratio which mean I would lose time and for me it’s hard to pick back up the momentum after stopping. Any suggestions?

    • Robert Kunz says:

      There are far too many variables here for us to recommend an exact plan, so its best if you practice some of this in your training. How you carry and how you consume your fuel is entirely up to you, however there are a couple things to remember. The fact that your hands were swelling is not just about sodium, its about sodium AND water. The science of osmolality delves into this, though its much simpler and equally as effective to use solution %. Remember that calculating your solution can be easy if you stick to 8%. For every 100 calories consume 12oz water. Whether its from a gel, bar, drink, stick to 120z fluid for each 100 calories. Because ONE EFS liquid shot flask is 400 calories, its very easy to carry. WE suggest you carry the flask, take a sip as you enter an aid station and chase it down with water. Practice this in your training so by the time you are finished you see how many calories and how much fluid you consumed. Most of our marathon runners will simply carry two EFS LS flasks in a small run belt and take water at aid stations. This is all they need to get to the finish, UNLESS its really hot.

      If your marathon is very HOT, then we suggest you change your plan to focus more on the EFS drink since it has a far stronger electrolyte profile. In this situation you may consider carrying a 12oz water bottle with some concentrated EFS drink (400 calories) and a 2nd EFS liquid shot flask. For the 1/2 half of the marathon sip on the drink and again chase it with water at aid stations. For the 2nd half of the marathon go to using the flask.

      Hope this helps.

  13. […] 560 calories worth of carbohydrates.  There is a great article on fueling during exercise here: The pre-event/training session meal eaten 2-3 hours prior to the workout or race should also be […]

  14. Christopher Harris says:

    Excellent article.

    If I consume simple carbs close to my long race (like a marathon or an ironman), will my body look to glycogen stores as a fuel source, rather than fat?

    If that’s true, why the recommendation to have some EFS 30-60 mins before a long race? Wouldn’t that spike my blood sugar and cause me to use my precious glycogen stores from the get-go?

    • Robert Kunz says:

      Great question. First you need to remember that it is not simple sugars that cause a sugar spike and crash, its high glycemic sugars that do this. A simple sugar like fructose is low glycemic whereas a complex carb like maltodextrin is high glycemic. If you add a protein or fat to any sugar you lower its glycemic index and hence eliminate the dreaded sugar spike and crash. Also know that once you begin to exercise insulin is blunted and sugar highs from high glycemic carbohydrates do not happen.

      Knowing this you can chose to consume a high glycemic drink like EFS 30-60 minutes prior to your event and you would still be OK not crashing. Remember however that we are not talking about chuggin 100 calories at 60 minutes out; we are talking sipping your bottle for the entire 30-60 minutes so you top off your glycogen/electrolytes prior to the start. OR, you can add in just a bit of fat or protein and stabilize your blood sugar. In this case you could start 60-120 minutes out and not worry.

      Know that pace determines which substrate is prefered (fat or glucose). In a high paced race glucose will be the primary fuel whereas in a sub-threshold pace fat will be the primary fuel. Regardless of what you consume your body will choose the appropriate fuel for the pace. Sipping on a high glycemic drink like EFS during high or low paced races conserves your glycogen stores because your body uses the orally ingested carbohydrate immediately instead of your stored glycogen. So regardless of distance or pace its best to consume high glycemic carbohydrates as your fuel source.
      So the only real no-no is to chug a high glycemic carbohydrate 60+ minutes prior to the start and then try to race without sipping on an appropriate drink. In this scenario you would start the race during a sugar crash and you would force your body to convert your stored glycogen into glucose to fuel the exercise. This would effectively cause you to use your glycogen prematurely and possibly cause a bonk on the latter part of the race.

  15. Cosmo says:


    I just finished my best Ironman race with a pr of 20 minutes. I’m frustrated because I probably left 20 minutes due to bloating on the bike. and sluggishness in t2. It was a 90 degree day.
    LOVE your products. I used in EFS lemon lime and shots. I hate to say I didn’t pee off the bike. Just in swim and run. I felt I drank enough without drinking too much. Any thoughts would be appreciated.

    • Robert Kunz says:

      Did you consume 12oz fluid for every 100 calories on the bike? including calories from liquid shot.

    • Robert Kunz says:

      Bloating is typically a result of a concentration percentage that is too high or more specifically osmolality that is too high. Its often the case when athletes consume calorically dense products like bars, gels or EFS liquid shot, without an appropriate amount of water. In these high concentrations water gets pulled from the blood into the gut and causes bloating. In HOT racing environments its critical to calculate your total caloric intake and compare with your total fluid intake. You should consume 12oz of water for every 100 calories to make sure fluid passes from the gut to the stomach not vise-versa.

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