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How to avoid bonking/hitting the wall


“Bonking” or “hitting the wall” is one of the worst experiences to have whilst out training or racing. This happens when you haven’t fuelled with enough carbohydrate before or during exercise, and you’ve used up most of the stored carbohydrate (glycogen) within your body. Here, we discuss methods to help prevent this.


Fuel for the work required in training


Carbohydrate intake will depend on the event you’re preparing for. Hard fast training sessions (such as intervals / fartlek training) are more dependent on carbohydrate as a fuel whereas slower steady state runs can be fuelled by using more of our own body fat stores. We’re always using some of both fuels, but it’s important to consider the use of fat as a fuel source as using fat during moderate-intensity exercise can “spare” our muscle glycogen stores for when we need them most i.e. hard intense exercise.

Given the concept of carbohydrate periodization (i.e. train smart), our nutritional plan for carbohydrate intake on training days should differ according to what the training goals are for that specific day, hence “fuel for the work required” (1). Some short, low intense sessions could be performed without carbohydrate (e.g having breakfast after and not before morning training) whereas for the hard effort sessions and very prolonged duration sessions, carbohydrate intake is essential. In such instances, carbohydrate should be consumed before, during and after the session. Additionally, “train as you race” sessions where we deliberately practice our race day nutrition strategy should also be included. This can teach our muscles how to use both fat and carbohydrate as fuels. The overall result of a periodized plan is that you turn up on race day with a physiological profile that is “ready-to-race”, prolonging our energy stores!


Carbohydrate loading


Focusing on your diet as you taper for your event will help you to maximise your energy stores. You don’t need a depletion phase before you carbohydrate load, and a period of increased carbohydrate intake with a training taper is sufficient to boost your glycogen stores. Follow these guidelines that consider carbohydrate intake based on the length of an event and your body mass (2):

  • Preparing for intense exercise under 90 minutes: 7-12 g/kg (of body mass) of carbohydrate 24 hours prior the event.
  • Preparation for events spanning over 90 minutes: 10 – 12 g/kg (of body mass) of carbohydrate per 24 hours, 36 hours before the event.
  • Immediate pre event fuelling for events lasting over 60 minutes: 2-3 g/kg (of body mass) of carbohydrate 1-3 hours before exercise.


Carbohydrate intake during prolonged exercise


Providing your muscles are loaded with glycogen and you’ve prepared well for your event, this stored glycogen will last for around 90-120 minutes of prolonged exercise dependent on your exercise intensity. Consuming carbohydrate during exercise maintains carbohydrate supply to the muscle as well reducing the reliance on your stored liver and muscle glycogen stores. Additionally, carbohydrate can also have a direct effect on the central nervous system and reduces the perception of effort during exercise. The ability of carbohydrate to stimulate the brain can even be achieved by simply “rinsing” a carbohydrate solution in our mouths, as opposed to actual ingestion.

Follow the below guidelines to ensure you fuel for performance (2)!

  • Brief exercise under 45 minutes: there may be no need to take on fuel during this exercise, focus on preparation


  • Sustained high intensity exercise of 45-75 minutes: fuelling may not be required if you have prepared well. Here, rinsing your mouth with a carbohydrate drink (e.g GO Electrolyte) can be an effective strategy. Rinse for 10 seconds at a time, every 10 minutes or so.


  • Endurance exercise > 90 minutes: Aim to take on 60-90 grams of carbohydrate per hour from multiple carbohydrate sources. 2* GO Isotonic Gels and 1* GO Electrolyte provides 80g of fast digesting carbohydrate. Aim to consume carbohydrate every 20 minutes and remember to start fuelling after 20 minutes of exercise, don’t leave it too late or you will not see the benefits!



    1. 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.
    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 Exercise, 48(3), 543.
Written By

Ted Munson (Performance Nutritionist)

Ted is a Performance Nutritionist here at Science in Sport.