Do Hilly Marathons Need More Carbs?

A Hilly Marathon Needs Only 0.5% More Energy

Most runners were taught that a hilly marathon burns more fuel, so they pack an extra gel or two for it.

To check that, we ran every course in CarbRate's course library through its energy model, which works out how much energy each mile of a course takes from its real elevation profile, with a flat course as zero.

The Marine Corps Marathon came out highest, at 0.5% more energy than a flat marathon. Hilly, rolling courses like Maine and Baltimore came out at 0.3% and 0.2%.

That means even on the hilliest course we've mapped, a runner taking 60 grams of carbohydrate an hour for 4 hours would need about 1 extra gram over the whole race. A gel has 22 to 40 grams in it, so the hills don't add even one. You can compare the grams in every gel with our free fuel finder.

Want to see how your fueling plan changes on your own course? Check out our course library, and if your race isn't there yet, send it to us and we'll map it for free.

Why Climbs and Descents Nearly Cancel Out

Running uphill costs more energy per mile, and running downhill costs less. Researchers measured this across slopes from steep descents to steep climbs, and CarbRate's energy model is built on their numbers.1

On a 2% grade, each uphill mile costs about 11% more energy than a flat mile, and each downhill mile costs about 10% less.

Most marathons climb and descend about the same amount, so the extra energy on the way up comes back on the way down. Each downhill mile saves you a little less energy than each uphill mile adds, which is why rolling courses still come out above flat, by tenths of a percent.

Downhill Courses Need Less Energy

A course that finishes lower than it starts gets more of those cheaper downhill miles. Using the Boston Marathon as an example, CarbRate's energy model shows that Boston needs about 1.5% less energy than a flat marathon, because its net downhill outweighs the Newton hills.

Big Sur, a course runners know for its climbs, comes out 0.5% below flat for the same reason, and the Tucson Marathon, which drops for most of its 26.2 miles, comes out 5.7% below.

Don't cut your carbs for a net downhill course either. On Boston, 1.5% less energy over a 4-hour race at 60 grams an hour is about 4 grams, a small part of one gel.

When a Hilly Course Does Add Carbs

Your carbs per hour stay the same on a hilly course. A hilly course adds carbs through time, because hills usually make your finish slower than it would be on a flat course.

As an example, if the hills on your course add 10 minutes to your finish and your plan has you taking 60 grams an hour, those 10 minutes need another 10 grams, less than half a gel. If you don't know your hourly target yet, our free fueling plan works it out from your body and goal time.

So set your carbs per hour from your plan, and count your gels from your expected finish time on that course.

Where You Take Your Gels on a Hilly Course

Blood flow to your gut drops by up to 80% after an hour at marathon effort, and it falls further the harder you work.23 A climb at race pace is usually the hardest work you do all day, so a gel taken halfway up a hill sits in your stomach instead of being absorbed.

Don't take your gels on any climb steeper than about 3%. Plan to take them on the flat before it, so the gel is already in your stomach when the climb starts, or on the flat after it.

Don't take gels on long, steep descents either. Below about 7% your quads are doing the braking and everything in your stomach is bouncing, so wait for the course to flatten.

These are CarbRate's own placement rules, and the full guide to when to take gels in a marathon covers the other 5 things that decide your gel timing, from water to aid stations.