How Much Harder Is It to Run a 15K vs. a 10K?

You've finished your first 5K, tackled the 10K and feel ready to take on a new challenge. You could aim to run either of those distances faster or set your sights on a half marathon. But there's another, less-common option to consider: the 15K.

If you can run a 10K, you can also run a 15K with these race training tips. (Image: Getty Images / Hero Images)

Preparing for, and running, the 15K will take slightly more time than a 10K. But overall, the demands on your body are similar, says Tim Bradley, a running coach and director of training for the Chicago Area Runners Association. Here's how this distance stacks up to the more popular alternative.

How Long Is a 15K Race?

The distance equates to 9.3 miles, compared to 6.2 miles for a 10K. Running a 10K involves reaching about 80 percent of your maximum heart rate and effort level, Bradley says. For a properly paced 15K, you'd only go about 2 to 3 percent slower or easier.

There's a critical difference at some paces: "For most people, the difference between a 10K and a 15K is running around or under an hour and over an hour," says Lisa Reichmann, a running coach at Run Farther and Faster, near Washington, DC.

That can mean you're close to your lactate threshold, or the pace at which your body produces a compound called lactate more rapidly than it can clear it away. It's difficult to sustain running at lactate threshold pace for more than an hour, she says. So, you'll need to pace yourself a little more carefully in a 15K than you would at shorter distances.

How Should You Train for a 15K?

Before you consider signing up for a 10K or 15K, it's a good idea to build up your running gradually and consistently. Aim for three runs of three miles or longer, three times per week.

From there, training programs for a 15K would look similar to those for a 10K. Ideally, you'd want to allow yourself between eight and 12 weeks to prepare. This affords you time to improve your fitness and increase your distance while also building in ample recovery, says Julie Sapper, who coaches with Reichmann at Run Farther and Faster.

You can train for either distance with three to four days of running per week, Bradley says. If you're a newer runner, this could include one longer run and two to three shorter runs, all at a relatively easy effort.

Intermediate runners can swap out an easy run for a speed workout, running a shorter distance at a faster pace, then jogging for a few minutes before doing it again. Shorter bursts of fast running — say, a quarter-mile — build your fast-twitch muscle fibers, which help more in the 10K, Reichmann says. Longer intervals, such as mile repeats, work well if you're training for a 15K.

And if you're an advanced runner, you can add a tempo run, which is an extended run at a comfortably hard pace. This type of workout can be especially beneficial if you're training for a 10K, because your tempo pace should be approximately the pace at which you'll plan to run the race.

The long run you'll do once a week will prepare you to cover the distance. You might start at around four miles and gradually increase — ideally, by no more than about 10 percent per week. If you're a newer runner or your goal is just to complete the distance, build up to at least six miles for a 10K and seven for a 15K. More experienced runners with a time goal might reach distances as long as 10 miles while training for a 10K and 12 to 13 miles for a 15K, Reichmann says.

Why Is Recovery Important for Runners?

As you build into longer distances of 10K and beyond, your body needs time and resources to bounce back from all your hard training. Every few weeks, decrease your long run and your total weekly mileage before starting to build it back up again, Bradley recommends.

Especially after your long run, make sure you refuel with a recovery shake or another suitable snack or meal, and Bradley also suggests using recovery tools such as foam rollers and recovery boots.

What Type of Cross-Training Should Runners Do?

Runners need more than just pounding the pavement to stay healthy and strong. Strength training decreases your risk of injury, and can also improve your performance, Reichmann says. Bradley suggests logging two to three dedicated strength-training sessions per week, but you can also break them up into a few moves done after each run. And don't forget to stretch after each run, too.

It can be tempting to skip some of these extras, but consider them a critical component of being a runner, especially as you tackle more mileage. "If you're willing to do the training, you should do the other things that will set you up for success," says Bradley.

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