The 1 Simple Mistake That Could Be Slowing You Down on Long Runs

It was after my longest run ever — 12 miles, at that point — that I got the hunch I messed up. The last two or three miles were a harder slog than they should have been; I felt like I needed a boost to snap me out of my physical fatigue and mental grogginess. I set out hydrated and well-rested and didn't have any nagging injuries. I also set out with nothing but a double espresso in my stomach and didn't consume any calories during the run. Rookie mistake.

My fueling fail prompted me to ask my coach, Bec Wilcock, to share the nuts and bolts on what to eat and when to eat on a distance run. Coach Bec is training my Nike Women's Marathon Project team (mercilessly, I might add) for the Chicago Marathon. Her own credentials are impressive: she's a seasoned ultramarathoner and all-around powerhouse who knows a thing or two about keeping your body fueled to tackle major tests of endurance.

Here's the simple science behind why it's vital to refuel mid long run: your body needs glucose (sugar) to burn. If it doesn't have it, it will move onto your body's glycogen stores. Our livers and muscles store glycogen, and once the muscle's stores are depleted, extreme physical fatigue — or "bonking," in runner's parlance — sets in. Read on for Coach Bec's advice on how to figure out what fueling plan works for you.

When to Eat

During a training run, Coach Bec says you should start thinking about nutrition by 90 minutes in. (For reference: I hit the 12-mile mark in about two hours the day I failed to fuel.) The rules are different on race day, however, when you should fuel even earlier and more often.

"It takes about 25 minutes until you break down glucose and start burning into your glycogen stores," Coach Bec says. In a marathon, for example, fueling every 30 minutes is a good benchmark to live by in order to avoid glycogen depletion.

What to Eat

There's a wide variety of gels, blocks, sport beans and other workout-specific fuels on the market, and they can range widely in calorie count. Some blocks, for example, have as little as 40 calories, while some gels have as many as 120. Most runners require somewhere between 100 and 250 calories per hour, depending on their body weight, so keep that in mind when you're choosing what to consume.

Coach Bec says it's essential to experiment with different products before a race to find out what works for you as an individual — and learn what fuels, if any, cause you any gastrointestinal distress.

I've found that gels are the easiest on my stomach, while blocks can sometimes bother me. I also prefer gels that include caffeine for a little added jolt of energy.

How to Eat It

One last piece of advice Coach Bec shared that hadn't occurred to me before: it's important to try to find a fuel source you actually enjoy. If gels gross you out, why suffer through them? If you hate having to put in the minimal effort to chew midrun, why force yourself to eat blocks?

Coach Bec suggests picking three favorite flavors to cycle through during your runs to help make fueling more enjoyable. "You want something you can look forward to so every hand to mouth movement releases a little dopamine into your system," she says. "Give yourself a little treat!"