With just a few miles to go, some runners can feel like they can’t go on. The most disciplined athletes I know have described this moment as dark and deeply existential, bringing them to tears. (Meanwhile, I can’t go more than six miles without digestive problems, and I cry at the slightest discomfort. I don’t stand a chance.)

“When you hit a wall, you usually have one big problem: Your gas tank is empty,” Milica McDowell, a physical therapist who has run 13 Ironman triathlons in addition to marathons, told Business Insider.

McDowell shared a few things marathon runners can do before and during the race to jump over the wall.

Training in refueling

It takes some time to get used to the right nutrition during a marathon.

“When you’re training for a marathon, you have to train not only your running training, but also your eating and drinking habits,” McDowell said.

The two most important things to focus on are adequate hydration and eating enough and the right foods.

McDowell said to drink fluids like water or Gatorade, about two to four ounces at a time, to avoid stomach upset. Tolerating four ounces at a time takes time, so she recommends working up to it as you exercise.

A typical portable water bottle is 16 to 20 ounces, and cups at water stations are usually around 4 ounces, she said. It’s crucial to be aware of how much and how often you hydrate before and on race day.

The second thing we need to focus on is consuming simple carbohydrates and glucose with about 200 calories per hour while running. Most marathoners do this with supplements, which come in a variety of forms, from gels to chewable tablets. I’ve seen people in my running group experiment with different brands and flavors during training to find what works best for them, whether it’s a caffeinated gel or an electrolyte drink.

“The last thing you would do is eat a meat bar or a granola bar,” she said. “Your body wants simple sugar — that’s what your muscles run on, your blood runs on, your brain runs on.”

Have a reset plan

McDowell said your brain also runs on glucose and that can cause you to experience a crash both mentally and physically.

According to McDowell, filling up on gas may make you feel better, but it won’t necessarily improve your mood.

Most new runners run 10 to 12 minutes per mile, she said. That means they reach the 20-mile mark of the race in about four hours.

“Most people are just not used to doing the same thing before that time,” she said. On top of the physical fatigue or cramping, they may feel restless, bored or agitated, and just want the race to be over =.

A quick trick is a physical reset. “Playing with your running form can be a really helpful distraction,” McDowell said. That could be running faster for a few minutes, taking smaller steps or moving your arms differently — anything to change things up and get yourself out of a rut.

If that doesn’t work, the reset may need to be more mental, she said. The key is to know what motivates you when you’re down, whether it’s an uplifting song, mantra, visual image or prayer.

“All those elements contribute to the psychological and mental resilience that you get from doing something like this for a long time,” she said.

Walk it off

My three goals for the marathon are: finish it, avoid injuries, and run the entire time.

According to McDowell, I might have to reconsider that last one.

From her experience coaching runners, she said a big part of getting over the wall is having a positive internal dialogue. If you have to slow down to a walk but tell yourself you’ve failed, “it only diminishes your performance,” she said.

She said most marathon runners, especially beginners, walk at least part of the race.

“It’s very common to walk through the aid station, it’s very common to do a run-walk program,” she said. “There’s almost a permission slip to consider that walking during training, and expecting walking during the race, is very normal and part of the process.”

Yes, training and fueling are necessary. But it is equally important to have compassion for yourself — especially in the tough moments.

“Those parts are really a special way for me to A: enjoy training and B: enjoy race day,” she said.