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The Importance of Caffeine

What is caffeine?

Caffeine is one of the most heavily researched and beneficial ergogenic aids available. It is mostly consumed in coffee, with 1 cup containing around 75mg of caffeine. The understanding of the performance effect of caffeine has increased and this has widened its use. Most people know that “caffeine may improve performance” but what does it actually do and how can we make the most of caffeine?


Why should you use Caffeine?

Caffeine acts centrally on the brain to lower the perception of effort, which is particularly noticeable in longer events such as running or cycling (1). In distance events over 90 minutes, mental tiredness as well as physical fatigue plays a large role in determining performance as the event progresses. Caffeine can help to maintain physical performance in this situation (2). Here are some of the main benefits that you can have by taking caffeine (1,3,4) :

How much?

Performance benefits of caffeine are well documented to occur in the dose of 2-6 mg/kg body mass (5). You should note, however, that caffeine in excess of 6 mg/kg has been shown to be detrimental to performance so it is definitely not a case of more is better. In fact, “more” will not only impair your performance but can also be dangerous to health.

Based on the dosing strategy above, this would equate to 150-300 mg of caffeine for a 75 kg athlete.

It has also been suggested that lower doses of caffeine (100mg and 200mg) at one time can show similar effects to high doses and can be just as beneficial to performance in some sport situations (6). However, tolerance of caffeine is highly individual and can be increased with regular intake. Always experiment in training and refrain from taking caffeine supplements in the late afternoon/evening as this may impair your sleep quality (7).

In most people, caffeine is absorbed in about 30 minutes after ingestion. The effect can last between 2- 4.5 hours and this depends solely on the individual. An GO Caffeine Shot is ideal to have 30 minutes before heading out for a 10k run, with the effects of caffeine lasting through the event. Combining carbohydrate and caffeine together has been shown to increase endurance performance(8). For longer events, or when you may need to top up with extra energy, GO Energy + Caffeine Bars provide both carbohydrate from oats and fruits as well as 75mg of caffeine.

Find out more about caffeine in our video below:

We have a range of products containing caffeine, including:

Other Related Articles:



    1. Killen, L. G., Green, J. M., O’Neal, E. K., McIntosh, J. R., Hornsby, J., & Coates, T. E. (2013). Effects of caffeine on session ratings of perceived exertion. European Journal of Applied Physiology, 113(3), 721-727.
    2. Miller, B., O’Connor, H., Orr, R., Ruell, P., Cheng, H. L., & Chow, C. M. (2014). Combined caffeine and carbohydrate ingestion: effects on nocturnal sleep and exercise performance in athletes. European Journal of Applied Physiology, 114(12), 2529-2537.
    3. Rosenbloom, C. (2014). Energy drinks, caffeine, and athletes. Nutrition Today, 49(2), 49-54.
    4. Rogers, P. J., Heatherley, S. V., Mullings, E. L., & Smith, J. E. (2013). Faster but not smarter: effects of caffeine and caffeine withdrawal on alertness and performance. Psychopharmacology, 226(2), 229-240.
    5. Tarnopolsky, M. A. (2011). Caffeine and creatine use in sport. Annals of Nutrition and Metabolism, 57(2), 1-8.
    6. Spriet, L. L. (2014). Exercise and sport performance with low doses of caffeine. Sports Medicine, 44(2), 175-184.
    7. Sökmen, B., Armstrong, L. E., Kraemer, W. J., Casa, D. J., Dias, J. C., Judelson, D. A., & Maresh, C. M. (2008). Caffeine use in sports: considerations for the athlete. The Journal of Strength & Conditioning Research, 22(3), 978-986.
    8. 8. Miller, B., O’Connor, H., Orr, R., Ruell, P., Cheng, H. L., & Chow, C. M. (2014). Combined caffeine and carbohydrate ingestion: effects on nocturnal sleep and exercise performance in athletes. European Journal of Applied Physiology, 114(12), 2529-2537
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Why Carbohydrate is King for Endurance Performance


Carbohydrate comes in a variety of forms. Sugars, including glucose, sucrose and fructose are all carbohydrates that you may have heard of. While they contain similar calories, they are all metabolized differently, thus affecting our performance output. Maltodextrin is broken down into glucose, which is the base of SiS GO Energy products. SiS GO Isotonic Energy gels, have been shown to get working in 15 minutes (1).


The digestion of carbohydrates for fuel begins when it first enters your mouth until it is absorbed into the bloodstream from the small intestines. The first organ to receive the broken down carbohydrates (glucose, fructose and galactose) is the liver. Here, glucose is either stored (as glycogen) or leaves the liver to be delivered by bloodstream to the muscles so that it may be used for energy . However, the type of carbohydrate that is ingested can determine the speed at which your muscles can use it for energy.

  • Must be converted into glucose in the liver before they can be metabolized (2)
  • Is oxidized at a much lower rate during exercise (2)
  • May cause gastrointestinal issues (stomach cramps/ sickness)
  • Sucrose
    • Also known as table sugar
    • A chemical combination of glucose and fructose
    • Has been shown to digest quickly (3)
    • Maltodextrin
      • Made up of chains of glucose molecules and has a high glycemic index (GI), meaning that energy is available quickly
      • Digested quickly during exercise (2)
      • Reduce the risk of developing gastrointestinal complaints during prolonged exercise (2)
      • At SIS, we use a type of maltodextrin with a particular size of molecule, known as its’ molecular weight. This allows us to balance the amount of energy delivered versus how quickly it empties from the stomach. This means that you will feel the performance benefits of taking on a SiS GO Isotonic Energy gel far more quickly than when a non-isotonic gel is consumed. The risk of upsetting your stomach is also much less. Energy gels with an osmolality close to the gastric content (i.e. isotonic) may promote high carbohydrate delivery to the small intestine compared to thick, concentrated hypertonic gels (4).


        It is common knowledge that some athletes and individuals claim to be “fat adapted” where they can completely use fat as a fuel source during endurance exercise. However, carbohydrate is the fuel for high intensity and prolonged endurance exercise. Although fat may provide more energy, it is used slowly. Carbohydrate yields more energy per litet of oxygen consumed and is a more efficient fuel, providing energy quickly to be used by the working muscles. Although an athlete can enhance the way they use fat a fuel source, potentially sparing muscle glycogen stores (5), race-winning performance is fueled by carbohydrates. As shown in the intensity vs. substrate use graph below, the body is always using a mixture of fuels for energy but this depends on the intensity of the exercise.



        Related Articles:

        • Which Gel, When?
        • The Only Isotonic Energy Gel
        • The role of protein for endurance athletes


          1. Patterson, S. D., & Gray, S. C. (2007). Carbohydrate-gel supplementation and endurance performance during intermittent high-intensity shuttle running. International Journal of Sport Nutrition and Exercise Metabolism, 17(5), 445-455.
          2. Jeukendrup, A. E. (2004). Carbohydrate intake during exercise and performance. Nutrition, 20(7), 669-677.
          3. Gonzalez, J. T., Fuchs, C. J., Smith, F. E., Thelwall, P. E., Taylor, R., Stevenson, E. J., & van Loon, L. J. (2015). Ingestion of glucose or sucrose prevents liver but not muscle glycogen depletion during prolonged endurance-type exercise in trained cyclists. American Journal of Physiology-Endocrinology and Metabolism, 309(12), 1032-1039.
          4. Zhang, X., O’Kennedy, N., & Morton, J. P. (2015). Extreme variation of nutritional composition and osmolality of commercially available carbohydrate energy gels. International Journal of Sport Nutrition and Exercise Metabolism, 25(5), 504-509.
          5. Impey, S. G., Hammond, K. M., Shepherd, S. O., Sharples, A. P., Stewart, C., Limb, M., & Close, G. L. (2016). Fuel for the work required: a practical approach to amalgamating train‐low paradigms for endurance athletes. Physiological Reports, 4(10), e12803.
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Marathon Running FAQs

How do I avoid "hitting the wall"?

Hitting the wall is when your body has depleted all glycogen stores and is "running on empty". To help prevent this, start taking on energy early during the race. Athletes often make the mistake of waiting until they're tired before they start taking on energy. However, the body always uses more energy than it can possibly absorb. Take your first SiS GO Isotonic Energy Gel after 20 minutes and continue feeding 60-90g of carbohydrate per hour (1). This will help 'top up' your energy stores throughout the race.

What should I eat before my marathon?

In the days before your marathon your training should taper, but carbohydrate intake should increase as part of a carbohydrate loading schedule. This involves taking in 8-12g of carbohydrate per kilo of bodyweight per 24 hours for 2 days (2). Avoid high fat, high protein and spicy foods. On the day, make sure you have breakfast 3-4 hours before and include normal breakfast foods that you have had before a training run. This should be mainly carbohydrate based e.g cereals, bread, fruit juice.

Runner with Isotonic energy gel

Do I only need gels on race day?

When preparing for a marathon, it is important to remember to plan in "train as you race" days. It's important to practice your sports nutrition plan during training to ensure that your body can tolerate it well. A good plan is to "fuel for the work required" that refers to days where you "train low" with reduced carbohydrate intake on those days when intensity and duration is not high and alternatively, plan days when you "train high" where you fully practice your marathon nutrition plan (3). This way, you're able to see the benefits of both fasted training and training with carbohydrate intake (4).

What's the best way to recover after my run?

Nutrition is one of the most important aspects of recovery. Recovery involves four main considerations; carbohydrate, protein, hydration and vitamin intake. Carbohydrate is considered the main recovery food, as this is the fuel that needs to be replaced so that you are able to go again. Protein assists muscle repair, while re-hydration helps the body's water to return to a normal state. Taking vitamins post exercise, particularly Vitamin C and Iron can help support immune function, which is suppressed after intense exercise. Ideally, take on a REGO Rapid Recovery shake within 30 minutes of finishing tough prolonged exercise, when the muscle's capacity to absorb nutrients is enhanced compared to resting conditions (5, 6).

Drinking REGO Rapid Recovery after run

I've heard gels can upset my stomach when you're running?

The more hypertonic a gel is, the longer it can take to digest and the more chance it has to cause stomach upset. Thick gels are mainly simple sugar based, which when ingested causes a fluid shift in the gut to help it digest (this is why many companies suggest you take water with their gels. There is also research to suggest that fructose can increase the chance of gastrointestinal distress (7). To combat this, take a gel that is isotonic, like the SiS GO Isotonic Energy Gel and try to avoid large volumes of fructose during exercise.

How often do I need to take gels during a marathon?

Aim for 60-90g of carbohydrate per hour (1). Using gels, this works out at 3 SiS GO Isotonic Energy Gels per hour. Remember; don't wait until you're tired before you start taking on energy. Take your first gel after the first 20 minutes. Try to combine the gels with other energy sources like that in SiS GO Electrolyte.

When should I use caffeine during a marathon?

Caffeine acts as a stimulant, decreasing your perception of fatigue (2). Caffeine is tolerated differently by everyone, but as a general recommendation, try to limit yourself to 200-300mg of caffeine on the day of the marathon. This could come from 2-4 75mg (caffeine) or two 150mg (caffeine) gels. Aim to consume your caffeine gel at least 30 minutes prior to when want you the desired performance effect. This could often coincide with 30-60 minutes prior to the last hour of your marathon.

Hydrating with GO Hydro

How much fluid do I need? It can be hard to carry a bottle.

This completely depends on your sweating rate, but it's important to avoid excessive dehydration throughout your marathon. Because hydration status and fluid intake is individual, try to aim not to lose any more than 2-3% of your body mass throughout the marathon (2, 8). Weigh yourself before and after training runs and calculate your body mass loss to estimate how much you are sweating. This usually falls around taking on 500-1000ml of fluid per hour during your marathon. This is especially important during training and racing in warm weather. Find out where your feed stations are and prepare to take a bottle!

Can I just drink water throughout the marathon?

Make sure you include electrolytes (such as SiS GO Hydro) in your water. To maintain hydration, we also need to maintain our blood sodium levels. We lose sodium through sweating and if we only replace our fluid losses with water, this could cause you to become hyponatremic (low blood sodium) (8). Sodium also helps retain and absorb fluid into the system.

Got a marathon question that’s not here? Leave it in the comments below and we’ll get it answered!

Related Articles:


  1. Jeukendrup, A. (2014). A step towards personalized sports nutrition: carbohydrate intake during exercise. Sports Medicine44(1), 25-33.
  2. Thomas, D. T., Erdman, K. A., & Burke, L. M. (2016). American College of Sports Medicine Joint Position Statement. Nutrition and Athletic Performance. Medicine and Science in Sports and Exercise48(3), 543.
  3. Impey, S. G., Hammond, K. M., Shepherd, S. O., Sharples, A. P., Stewart, C., Limb, M., & Close, G. L. (2016). Fuel for the work required: a practical approach to amalgamating train‐low paradigms for endurance athletes. Physiological Reports4(10), e12803.
  4. Bartlett, J. D., Hawley, J. A., & Morton, J. P. (2015). Carbohydrate availability and exercise training adaptation: too much of a good thing? European Journal of Sport Science15(1), 3-12.
  5. Atherton, P. J., Etheridge, T., Watt, P. W., Wilkinson, D., Selby, A., Rankin, D. & Rennie, M. J. (2010). Muscle full effect after oral protein: time-dependent concordance and discordance between human muscle protein synthesis and mTORC1 signaling. The American Journal of Clinical Nutrition, 92(5), 1080-1088.
  6. Ivy, J. L., Katz, A. L., Cutler, C. L., Sherman, W. M., & Coyle, E. F. (1988). Muscle glycogen synthesis after exercise: effect of time of carbohydrate ingestion. Journal of Applied Physiology64(4), 1480-1485.
  7. de Oliveira, E. P., Burini, R. C., & Jeukendrup, A. (2014). Gastrointestinal complaints during exercise: prevalence, etiology, and nutritional recommendations. Sports Medicine, 44(1), 79-85.
  8. Casa, D. J., DeMartini, J. K., Bergeron, M. F., Csillan, D., Eichner, E. R., Lopez, R. M., ... & Yeargin, S. W. (2015). National Athletic Trainers' Association position statement: exertional heat illnesses. Journal of Athletic Training50(9), 986-1000.
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