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When you first consider signing up for a marathon, a little voice in your head will throw up a number of scary prospects to try and make you think again. But one thing stands tall above the likes of lengthy training runs to make any would-be runner reconsider their choice: the wall.
But what exactly is the wall, why do you 'hit it' and how can it be avoided? Here, world-leading sports scientist and director of human performance science at The Centre of Health and Human Performance, Professor Greg Whyte OBE, and Steve Grant, a nutritionist specialising in sport and athletic performance, explain the facts.
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The wall explained
"Traditionally we regard the wall as the point at which you run out of energy," says Whyte.
It’s the point where it feels like you can’t go on and someone’s almost taken the plug out. The caveat in there is that it does tend to coincide, as well as energy levels, with physical capacity – so pain in the legs, hips and lower back. The wall is different for each individual, but traditionally we see it as running out of energy.
"There are three ways we can produce energy – carbohydrates, fats and proteins," explains Whyte, "and invariably, it’s about the speed of demand for energy that dictates what energy source we use. Generally, in endurance and ultra-endurance, we use a combination of fats and carbohydrates.
"The main thing that the wall describes is getting to a point where you've depleted your main energy source – glycogen," expands nutritionist Grant. "We all store carbohydrates in the form of glycogen, and we can store about 500-800g of carbohydrates both in our liver and in muscle tissue.
"When your body is depleted of glycogen, you have to utilise other external fuel sources, which is called gluconeogenesis. Your body can make glucose out of things that aren’t glucose, through utilising fats and somewhat less efficiently, using proteins, but with both you’re not able to make energy as effectively."
When are you most likely to 'hit the wall'?
"Assuming they’re not following any fuelling strategy, most people will hit the wall around two to three hours in," reveals Grant. "It will vary a little bit depending on how hard they’re working during the event, what their fitness level is like and how much they trained before the event."
Whyte agrees: "As well as it being energy dependent, it’s also about conditioning. It depends on how much training you’ve done, but if you’re well prepared, most people describe the 18-mile point. That’s the classic area where you really start to 'hit it'. You get a combination of energy depletion and pain and muscle damage, which also leads to a point of misery where it starts to become really tough."
Does everybody 'hit the wall'?
Not everyone will hit the wall during a marathon. And although there are many variables that contribute, much of it comes down to how prepared you are – in terms of your physical training and nutrition strategy.
"A general rule of thumb when preparing for any event is that you try and hit 80 percent of the target distance," says Whyte. "If you’ve done a 20-22 [mile run] in prep for a marathon, generally you'll fair well. It’s the people who don’t get those long distances in that suffer more.
"The other aspect is strategy – both feeding and fluid. Those people who [have trained for the distance have also] train[ed] those strategies, so they’re much less likely to run out of energy or become dehydrated."
Grant adds that some may have even trained their bodies to delay the onset of the wall.
"Some people will be able to delay the process by becoming slightly more fat adapted, in the sense that they’re used to using [fat] as an energy source as part of their training. Those people can utilise lower carbohydrate diets to essentially force the body to be better at using fats as an energy source. What you get is metabolic flexibility, which is the body’s ability to switch from using carbohydrates to being able to easily use fats.
"The ideal situation is that someone has really good metabolic flexibility in that, when they do higher intensity work, they can tap into glycogen, and when working at moderate-to-lower intensities, they can go primarily to fats as a fuel source. By doing that and being better at that, you can spread the glycogen for a longer period of time."
How do you prepare for a wall-free race?
Your nutrition strategy in the week leading up to a race will be critical to preventing the wall, explains Grant.
"It's really important to taper off the training in the run-up to the event, but to carry on eating in the same way as if you were training. The reason for that is that you’ll steadily replete your glycogen stores. And if you've been doing a lower carb approach, you would actively bring in more carbohydrates during that week in the run-up to the event, so you can ensure the glycogen stores in the liver are replenished as well.
"I tend not to like doing carb loading the night before with people because it can tend to upset someone’s stomach or they'll have a poor night’s sleep and feel sluggish the next day. For me, the replenishment of glycogen starts in the week before, and you steadily bring down training so you’re not depleting glycogen.
"Finally, on the morning of the race, I’d recommend having a fairly balanced breakfast with a good level of carbohydrates in it – at least 100g – and maybe some fruits, eggs or nuts."
What can you do during your run to prevent hitting the wall?
"The way for us to prevent 'hitting the wall' is to replenish the body with some simple form of carbohydrate during the event," says Grant. "By drip feeding some glucose into the system, you’ve got some available energy there that gets delivered to the muscles. Aim to take a little bit on every 30 minutes or so. Ideally you don’t want to wait until you’re depleted before bringing stuff in because it’s much harder to pull yourself back than keep topping yourself up as you go through.
Glucose can be topped up through carb-based drinks, such as Red Bull, or through gummy sweets, which are easy for the body to digest. "As a really general rule, you probably want to go for somewhere between 30-60g of carbohydrates per hour during the event," says Grant. "If you start moving above that, you can often cause an upset stomach, which might mean you need to rush to the toilet which isn’t ideal during an event, or you can get cramping."
Grant does have a word of warning, though: "What is really important is that you train your gut to be able to tolerate those things for the event day. If you turn up on the day having not done any carb drinks or gels during training, and you suddenly start throwing them in on the day because they’re handing them out on the side, it will often cause a lot of digestive upset and potentially embarrassing situations."
What to do if you 'hit the wall'
"If you do 'hit the wall', feeding is the way forward," says Whyte. "What you’re looking for is something that gives you as rapid an energy boost as possible. This is generally high glycemic index foodstuffs, or in other words, jelly babies, fruit pastels and sports gels." He adds that it's important to take it slowly though as overloading can cause GI distress, which can lead to nausea and bloatedness, and the extreme of that is vomiting or diarrhoea.
And in terms of running, Grant recommends the following tactic: "Bring the intensity down first, maybe walk for a bit and grab a drink. Don’t try to guzzle it down: have some sips, and then you’re slowly bringing the carbohydrates into the system in incremental stages, to help avoid upsetting the digestive system."