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Fuelling For Performance

How to begin fuelling in workouts for better race-day performance.

If you are someone who enjoys pushing the limits of your own endurance, odds are you have come face to face with this experience. The "Bonk". A notorious phenomenon known among endurance junkies across many different sports; triathletes, cyclists, and runners alike have experienced this dreadful affliction. You're out for a run, a bike . . . an adventure! It's hot, you're pushing the pace a bit, but you feel good and are enjoying the workout. But then, around the 90-minute mark, you're not so sure anymore . . . your legs begin to slow, and you feel like you're moving through molasses. You are working harder and harder, but your speed continues to diminish. You have arrived; you are bonking.

Personally, these experiences primarily come from training sessions where I was unprepared with proper hydration and fuelling. A specific run comes to memory, of a time when an easy 60-minute run turned into a 2-hour suffer-fest. I was running in a new town and explored the waterfront trail, but when I tried to loop back to where I started, I continually found my path intersected by a fenced railway topped with barbed wire. The longer I ran, the more lost I became. My progress back home was painstakingly slow. The day was hot, and I found myself dehydrated and de-fuelled! After about 90 minutes, even my typical easy pace slowed drastically and I struggled to maintain a shuffle. With my muscles depleting of glycogen and electrolytes, their function impaired and my performance suffered. Had I proper fuel to replenish, I'd likely have been able to continue on my run without a big drop in my paces and a big spike in my level of exertion. So here follows my antithesis to bonking, as I have begun to branch into ultramarathon endurance events where the need for proper fuelling strategies becomes increasingly important for success (and even enjoyment!).

Fuelling during workouts and races is often a very misunderstood concept. This is disappointing because learning how and when to take in nutrition during a workout or a competition will improve your performance in that given activity, as well as reduce the overall stress and level of exertion the activity induces. Moreover, fuelling during workouts is actually a trainable factor, meaning our body can actually improve its ability to absorb and efficiently metabolize carbohydrates, electrolytes, and water!

Why Fuel?

When we talk about "fuelling" in this article, we are primarily referring to carbohydrate intake during exercise. Glucose is the primary fuel source our muscles use during endurance races of moderate to high intensities, so keeping our muscles consistently supplied with fuel means we can race faster for longer! Who wouldn't want to be able to run faster and farther? Our bodies typically have enough glycogen stored within our muscles to exercise at a moderate to high rate for around two hour. Once we get toward that 90- to 120-minute mark and our glycogen stores begin to near depletion, our energy production shifts more heavily toward fat oxidation; a slower process than glycolysis, resulting in a slower pace. Our muscles don't need to reach full depletion to begin experiencing performance detriments. But at its worst, when muscles do reach near glycogen depletion, we "bonk". Therefore fuelling early and often during longer endurance events (workouts and races) will help us stave off fatigue, and continue to work at a high effort for long durations.

The longer the event, the more important nutrition will become. Ultramarathons of 100-miles and longer are often referred to as "eating contests" as much as running contest, because athletes that can consume and utilize the most fuel are more likely to be successful than their under-fuelled opponents. However it is not as simple as running and simultaneously stuffing your face. When we exercise, our body diverts large portions of blood from our GI tract (stomach and intestines) to the working muscles. Although this is ideal for the working muscles to receive greater oxygen supply, it means our gut's ability to function is reduced. Fortunately, similar to any part of our training, there are beneficial adaptations to be earned through practicing fuelling during workouts. Thats right, your gut's ability to digest, absorb, and utilize carbohydrate during endurance events is actually a trainable factor! Whereby practicing fuelling during endurance training we improve our GI tract's ability to absorb and efficiently utilize more fuel during exercise.

Do I need intra-workout fuelling?

If you are wondering if this even concerns you, if you need to be worrying about fuelling with carbohydrates during your workouts, then look to these 3 simple criteria. We use these questions with our athletes to help them determine if intra-workout fuelling will be advantageous for them to incorporate into their training and racing.

1) Is the workout 90-minutes or longer in duration?

Shorter workouts that are less than 90-minutes can be sustained solely by the glycogen stored within our muscles. Especially if these workouts are lower intensity, such as recovery runs, easy mileages, and shorter cross-training sessions, then no fuelling is necessary.

2) Is the workout moderate-high intensity, where performance is important?

The primary reason we are looking to add a carbohydrate source during our workouts is to ultimately improve our performance across the session. We are aiming to mitigate fatigue due to glycogen-depletion, which will affect our ability to maintain a higher intensity across the workout (i.e. higher power output on the bike or faster paces on the run). Intensity sessions that last 90-minutes or more will see great performance benefits from fuelling throughout the workout. The best examples of when to fuel are during big training sessions such as a marathon-specific long run, or a bike-run brick session. These are also ideal sessions to dial in your fuelling strategies for race day! Conversely, if the goal of a session is not performance-based, such as fat-loss or general exercise and movement goals, or a HIIT fitness class, then fuelling during the session are not necessary.

3) Are you preparing for an event that is 90-minutes or longer?

The first 2 criteria are my most important, however I added this third point later as I thought more and more about track athletes; although many of their interval sessions and long runs last 1-2 hours and are performance based, their competition events only last from ~2 minutes to 15 minutes. These athletes can still benefit greatly from intra-workout fuelling, because it will improve their performance within workouts and that will lead to greater adaptations, as well as reduce the overall stress placed on the body (improving recovery). For these reasons I would recommend athletes training for 800m up to 10k still utilize intra-workout fuelling. If it improves their training it will likely improve their performance on race day. However it is not as essential compared to athletes training for marathons, long course triathlons, and ultra marathons who are also looking for the additional gut-trainability benefits for enhanced fuelling that will be essential for success during their actual competition event.

How do I fuel during workouts and races?

Time for the practical applications! For long-distance athletes fuelling should be practiced at least once per week, ideally during your longest and most specific workouts (remember the criteria above). For triathletes this would be during large bike-run brick workouts. For Marathon and ultramarathon athletes this would be during their long runs, especially when they begin to include elements of tempo and race paces.

The simple rules of fuelling during training and races are fuel early and fuel often! The best analogy I've heard is that fuelling is NOT like a gas tank (run it 'til it's empty then fill 'er up), but more like a phone battery; the more you drain the battery, the longer it will take to recharge. So by replenishing glycogen stores early and often, you'll be able to sustain a consistent level of fuel. Start fuelling 45 minutes into a training session, and then every 20-30 minutes after. Most individuals can utilize 30-60grams of carbs/hour, and with practice you will improve to the higher side of this range. This is why most gels and carbohydrate drinks contain ~22-30g of carbs per serving, in which case a beginning strategy would be 1 gel every 30-minutes totalling ~60g/hour. In more trained individuals, utilizing as much as 70-120g/hour is possible (thats a lot of gels)! The more carbs our body can successfully absorb during exercise, the better we can stave off glycogen depletion and continue to perform at a high intensity. With these larger ranges of carbohydrates, they are better absorbed in smaller and more frequent doses to give your gut the best opportunity for assimilation.

GI Distress (aka tempo tummy)

Some of us are iron-stomach runners, and can wolf down everything but the kitchen sink without much issue. Yet many of us are much more sensitive to what goes into our stomachs around and during workouts. If you are typically more prone to GI distress when you exercise, there are a few ways to help improve your stomach's tolerance within these endurance events so that you are able to effectively fuel on race day. First, you will want to practice fuelling much more often throughout the week (i.e. 3-4 sessions) regardless of how short the workout may be. Even a 30-minute run can include a gel within the last 10 minutes (when you are within closer proximity to your bathroom). It can be easier to start practicing fuelling on low/non-impact modalities such as cycling or elliptical. These modalities are much easier for carrying bottles with carbohydrate drinks and gels, plus the lack of impact and resultant jostling on the stomach is much friendlier. In addition, caffeine is a common ingredient in many gel and sport drink products, as its performance-enhancing benefits are well-supported by science. However I would also suggest staying away from these products with caffeine if you are prone to GI distress, as it can commonly be a stomach-irritant for many athletes during exercise. Even for the iron-stomached athletes out there, I would suggest to using caffeinated products sparingly during these events; if you are going use 6-8 gels throughout a marathon and they all have caffeine, it could be equivalent to drinking several espressos! I recommend athletes use 1 or 2 caffeinated products in succession during a particularly tough portion of a race to get a significant boost, such as at the 28-32km mark of a marathon.

There are many products out there, and companies and athletes are becoming increasingly creative. Maple syrup, honey, and other more natural products are on the market and performing successfully. Ultra runners will even practice with their own home-made snacks, as longer races (think over 10 hours) will benefit from more solid foods in addition to gels and drinks.

But remember these are recommendations, and your specific strategy will need to be PRACTICED and ADJUSTED to find what works best for your body, your event, YOU!


Pöchmüller M, Schwingshackl L, Colombani PC, Hoffmann G. A systematic review and meta-analysis of carbohydrate benefits associated with randomized controlled competition-based performance trials. J Int Soc Sports Nutr. 2016 Jul 11;13:27. doi: 10.1186/s12970 016-0139-6.


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