It’s crunch time now for those who have been training for this year’s London Marathon.

While the bulk of training is done now, there’s perhaps more to think about than ever for the nearly 50,000 people running on 21 April.

We’ve spoken to a sports therapist, a dietitian and a man who has run every London Marathon to find out the most common pitfalls before and during a race – and how you can avoid them.

“This is the time when a lot of people lose their head,” warns sports therapist and physio Gabriel Segall.

So how much should you be running now? Should you make changes to your diet? What should you eat before the race – and how can you avoid the dreaded wall?

Preparedness for a marathon can be broken down into three main categories, says Gabriel:

• Training load
• Recovery
• Diet

Training load, he says, should be largely covered by now, with all your gruelling trial runs out of the way ahead of the 26.2-mile challenge.

He says participants will hopefully have tried to complete 20 to 23 miles in their training runs, as that will have given their bodies “the experience of having that stress through it” and some muscle memory when it comes to coping with a marathon.

But the week before the marathon is crucial, and often where people make mistakes that will hinder their success.

Mistake #1 – Cramming

Cramming in last-minute work like you’re revising for a test simply won’t cut it. In fact, it will likely be detrimental to your performance, Gabriel warns.

“If you keep pushing and train too hard, a lot of people get injured or ill because they don’t give themselves enough time to recover. And that’s where people can struggle.”

A four-time marathon runner himself, Gabriel instead suggests accepting where you are in your training and adjusting your target finishing time accordingly.

Chris Finill is one of just seven people who has completed all 43 London Marathons since its inception in 1981. He and his wife – who has also been to every event with her husband, either supporting him, medal hanging or running herself – have seen a lot of runners come and go over the years, and unrealistic targets have been the downfall of many.

Speaking to Sky News in the lead-up to his 44th, the 64-year-old says: “People tend to choose an unrealistic target and are too optimistic in the time they can achieve. And once they’ve worked out what pace they need to run right to achieve that unrealistic time, they run even faster than that in the early stages because they feel so fresh.

“So the golden rule is to preserve energy and hold back however excited, exuberant or energetic you feel in those first few miles.”

Mistake #2 – Not winding down before the race

People should be winding down their training and focusing on recovery, Gabriel says, in what’s known as tapering.

Chris, who’s hoping to finish in under three hours, says he’ll “hardly run at all” in the last three or four days before the marathon, though he may complete a two-mile jog the day before.

“The tapering period is a time to let the body relax,” Gabriel says. “You’re not going to have a massive increase in fitness or performance in the last couple of weeks.”

He highlights the pyramid of recovery, which outlines the optimal recovery strategies for athletes, going from bottom to top in terms of importance.

He also warns against being too influenced by social media when it comes to your preparation.

“You see lots of athlete and runner influencers online talking about the best ways to recover,” he says. “They seem to go out, run really hard and use all these products that they probably influence and get you discounts on, then they go out for a pub night and get two hours’ sleep.”

This form of training might seem idyllic, Gabriel says, but it’s not realistic.

“There’s one real way to recover – and that’s sleep,” he says. “Sleep is your absolute best recovery.”

Chris, who is retired, says he does his best to be in bed by 11pm latest and gets up no earlier than 7.30am if he can help it.

Beyond sleep, Gabriel says “active recovery days” are becoming increasingly popular, where you do some form of very low intensity exercise like going for a walk, stretching or similar activities that relax your body.

Mistake #3 – Getting the carbs wrong – and last-minute diet changes

A runner’s diet is different to what you typically associate with a healthy one, and it’s well-known that the most important thing is carbohydrates, says nutritional therapist Monica Price.

“It breaks down into glucose, and then we store that in our body aside as glycogen, and then that’s stored in our liver and our muscles, and our body uses that to give us energy,” she tells Sky News.

She says those training should already have upped their intake significantly, and “at least 70% of your diet should be carbs” going into the last week.

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So if you’re peckish and go to grab an apple, trade it for a slice of toast or a scone, she says.

However, not all carbs are created equal, and there is such a thing as overdoing it.

Having too many carbs when your body isn’t used to it could mean you feel like you’re running “after a Christmas dinner”.

Monica suggests “simple” carbs such as bread, pasta with tomato sauce, rice, potatoes, chicken, fish and tofu. While brown carbs are often encouraged by dieticians for their fibre, for runners they’re more likely to upset your stomach, Monica says.

It’s vital you don’t change too much about your diet leading up to the big day, she adds, because changes should be largely “trialled and tested” beforehand.

Mistake #4 – Incorrect fuelling = hitting “the wall”

The wall has long been a part of marathon folklore. Also known as “bonking”, it is “a wall of fatigue,” Gabriel explains.

“Some runners, not all, just hit this wall where they can’t do anything more. It can happen for multiple reasons, but it’s often due to not fuelling correctly.”

Monica adds: “You’re physically exhausted. Your legs can’t move, you go into muscle cramps, you have a spasm, you see, you feel dizzy and you completely collapse – and your brain is saying ‘no more’.

“And that happens because your body is running out of glycogen. In other words, you haven’t had enough carbs in your diet.

“That’s why you see runners collapse to the ground. It’s also key that during the race you have plenty of fluids, including sports drinks.”

Gabriel says pacing yourself will reduce your chances of hitting the wall, as Chris attests.

“I wouldn’t say I’ve ever hit it [the wall] in any significant way. I’ve had good races and bad races, but I’ve generally managed it by taking gels, having an energy drink and not going off too fast,” Chris says.

It can impact you mentally too, Gabriel says, because the brain requires glucose, which it isn’t getting if you aren’t fuelling correctly.

While refuelling and pacing yourself is a necessity, he says, mental fortitude is just as important.

“Focus on why you want to run and on the strategies you’ve learned during your training,” he says. “Trust yourself and the work you put in. This is just the home stretch.”

So how should you prepare the day before?

Monica says runners typically eat smaller, easily digestible meals every few hours the day before a race, while keeping carbs in mind. Think breads, sandwiches and bagels, as well as things like chicken, rice and noodles.

“And keep drinking water,” she says. “That’s always essential.”

Chris adds: “I always suggest people should eat relatively early, so you’re not going to bed on a full stomach – say by 7pm. But don’t go to bed too early.

“It sounds slightly counter-intuitive, but I think if you go to bed early because you’ve got a big day to follow, you just lie there and toss and turn. If you don’t get a good night’s sleep the night before, it’s not that important if you slept well on the nights before that.

“If you wake up on Sunday morning feeling like you’ve only slept for a couple of hours, I really wouldn’t worry about that. Try to put it to the back of your mind and just focus on the day ahead.”

What to eat on Sunday morning

Monica recommends a bagel with peanut butter and banana, as it’s got the carbs, protein and potassium you’ll need – though she concedes most runners tend to go with porridge or Weetabix.

It’s not uncommon, however, for nerves to prevent you being able to eat anything at all.

“Most runners are going to be nervous – professional runners or novices,” she says. “So don’t panic if you haven’t been able to stomach the breakfast or you’ve tried and brought it back up – that happens.”

She says it’s more important that you have carbs stored up from the hours and days before Sunday.

Accept that something will probably go wrong

Most runners know that 9/10 runs “aren’t great”, says Gabriel.

“You can do all the training you need to for the months and months and sometimes it just doesn’t hit. You don’t have a good day. Your legs might feel rubbish or your breathing may feel off,” he says.

“Don’t panic, or stress, whatever happens,” Gabriel says.

“Take a minute to just sort yourself out if you need to. Have a drink, have a gel, and remind yourself of why you’re doing it.

“That can really push you through, and the beauty of the London Marathon is there’s so many runners around you all on the same journey.”