And we all know it’s not just the physical training that gets us through, it’s also our minds telling us not to give up.
But some people decide to go one step further, taking on extreme fitness challenges like a series of marathons in consecutive days.
So how do they do it?
Mental toughness is crucial in achieving success, and having the ability to persevere when your body is telling you to stop.
“Your mental training is just as important as your physical training, your hydration, your nutrition, your race plan,” Carrie Cheadle, expert in mental skills training and author of ‘Mental Skills to Maximize Your Athletic Performance’ told HuffPost UK. “It’s another spoke in the wheel.”
“Any fitness performance is 50% physical and 50% mental,” said Cheadle.
“You would never show up to your event not having done your physical training and preparation, so why show up not having done any of your mental training and preparation?”
Some people may take on a fitness challenge feeling confident from the start that they’ll get to the finish line.
Keith Simpson ran 26 marathons around the world in alphabetical order. He was 64 when he ran his first marathon. Simpson didn’t train himself mentally, because he has always “accepted things as they happen in life” and has never been a worrier.
“Marathons are never easy, and there is no way of predicting how any race will go,” he told HuffPost UK.
“But I always feel if I get past 20 miles feeling OK, the last six miles will not be a problem. With that attitude, not too many races have been real struggles.”
But Cheadle said anyone can “reach into the depths of their mind” and pull out strength they need to get through a challenge.
“I tell my athletes that it’s their physical preparation to get them to the start line and their mental preparation that gets them to the finish,” she said.
“Anyone can perform well when they’re having a great day, the stars are aligned, and everything is going exactly the way you wanted it to. But rarely is there an event where you’re not faced with some unforeseen challenge or obstacle.
“Your mental strength is what helps you get through those challenges and be able to continue on the path to your goal.”
Phil Payne, 32, has completed a range of challenges including the Iron Man, Marathon des Sables and a 100-hour spin. He said all these have been more mentally challenging than they have physically.
“It’s just a question of telling yourself that this feeling won’t last forever and just how good it will feel when you overcome it,” he said, explaining how his mind helped him get through.
“Having people behind you and support helps loads and having a reputation of doing things that most people can’t do is a boost as you want to maintain that.
“Some of the quotes from ‘Rocky’ films help me loads, too. I replay them in my head.
“Mental resilience is about not being afraid to go into that dark place where no one is around and you feel so, so alone.”
Teaching yourself to be strong is possible, but not easy. Amy Hughes, who ran 53 marathons in 53 days.
Amy Hughes, who ran 53 marathons in 53 days, as well as running 521 miles on a treadmill in one week, puts her successes down to mental preparation.
“Teaching yourself to be strong is possible, but not easy,” she told HuffPost UK. “My training consisted of more mental preparation than physical.”
“I tried to get more hours on the road than miles so mentally I knew I could stay on my feet. I also tried not to focus on the negatives. It’s easy to get wrapped up in what experts say you ‘should’ be doing.
“It’s easy to let the negatives take over. It’s easy to let worry and self doubt take over but once that goes, it’s hard to pull yourself through tough times.”
But that’s not to say it came easy to Hughes. In every challenge she’s undertaken, her mental strength has been tested to the extreme.
“I am the most stubborn person I know, so that is a big help, but sometimes it’s hard to breakthrough the pain barrier when you feel like you can’t go on,” she said.
“It might sound a bit cheesy but I created a mantra. When I get tired or really want to quit, I repeat it in my head and it slowly turns my self doubt into ‘I’ve got this’.
“I don’t know where it came from or why I chose these words but it’s: ‘You are strong, you are fearless, don’t stop’.”
Gaining mental strength is a process, said Cheadle, and not something that will come with the click of your fingers.
“Mental toughness is absolutely something you can develop,” she added. “Your mental skills are just like physical skills in that they can be built and strengthened with training and practice.”
Cheadle said it’s down to three things:
“Motivation might be the thing that gets you going, but commitment is what keeps you going,” she said. “When you are committed to the goal, any setbacks you encounter are temporary and it’s not a matter of if you accomplish your goal, but when.”
“One of the characteristics of mentally tough athletes is that they are able to perform under pressure and able to perform consistently,” she said.
“When you are mentally tough you stay in the present moment, keep your focus on the things that are in your control, and aren’t distracted by things irrelevant to your performance.”
“You have to believe you can do this,” she said. “Mentally tough athletes have an unshakeable belief in their ability to accomplish their goals and know that one bad day doesn’t define them.
“You use failures as feedback. Failures don’t make you want to throw in the towel, they make you want it even more.”