One of the steps to becoming a better runner is running more miles. That’s particularly true if your goal is to compete in longer races like the half or full marathon, where you need endurance just to finish the distance. It’s equally true, however, if you never plan to race over the 5K, or to race at all. Elite runners put in up to 100 miles or more per week to be their best. You don’t need to run that much, but running more will transform your body. Miles build aerobic strength, enhance your ability to turn oxygen into energy more effectively, and make you a leaner, more efficient running machine.

Increasing your miles needs to be done carefully, however. Because of the additional stress on your body, you risk getting injured, or sick, or just sick and tired of running. You want to build gradually, ideally over a period where you don’t have any races, so your primary goal can be to build a strong base of fitness. Whether you’re just starting to get serious or you’re at a plateau, laying a foundation of more miles will take you to the next level. Here are some tips to ensure your new miles will build you up rather than knock you down.

Slow Down On Easy Days

If your goal is to increase endurance, you have to stop worrying about speed on every run. You need to run fast some days—to improve your speed, stride and stamina—but successful runners limit fast work to less than 20 percent of their total miles. Ignore whatever is compelling you to run faster, whether it a training partner, habit or your Strava feed. Running faster than you should on easy days leads to injuries, or, at minimum, makes you too tired to run more miles the next day, which is your goal.

Not only do your muscles work harder when you run faster, but impact forces increase with speed as you fly farther with each stride and drive into the ground harder to propel forward. Slowing down can, however, increase impact if your form deteriorates. To reduce stress on your joints and muscles, don’t slow down your cadence and start loping or plodding. Instead, focus on shortening your stride while maintaining your turnover. Research has proven that a faster cadence reduces impact, while increasing oxygen consumption. To maintain the effort while sparing your legs, stay tall and let your stride roll quickly and comfortably beneath and behind you, settling in to an efficient, easy glide that eats the miles.

READ MORE: How Cross-Training Can Improve Your Running

Run More Often

This feels like a no-brainer, but it is surprising how often we ignore it. The easiest way to run more miles is to do more runs. If you’re currently running three times per week, adding a short run on two or three additional days will boost your miles significantly. Don’t discount any distance as too short: Small runs, done regularly, compound into big totals over weeks and months. And, if you keep those miles easy (see point #1), those days can still be recovery days. In fact, a short run on your “off” day can make it easier to show up for your next workout by increasing blood flow, which enhances recovery. Plus, it reinforces the habit, making running the default option.

If you’re already running five to six times a week, adding a second run one or two days can be easier on your body than going longer on your current runs. You’re more likely to get hurt during the latter miles of a run when you’re fatigued and your form starts to fall apart. So, two 3-mile runs in a day is easier on you than one 6-mile run. Since you want some of the stress of going long to stimulate endurance, coaches recommend that you split the runs asymmetrically. Instead of heading out for one 6-mile run, for example, you could run 5-miles in the morning and 3-miles in the afternoon, increasing your volume without beating up your legs too much.

Switchback Your Increases

The most direct way over a mountain is to head straight up it, right? Few mountain roads, however, follow such a straight, impossibly steep route. Instead they follow switchbacks, cutting more gradual gradients across the face of the mountain and doubling back, recovering regularly with a level section or even a slight decrease in elevation. A smart ascent up the mileage mountain follows a similar route.

Training works by first tearing down the body, then giving it a chance to respond to this new stress by building back stronger so it can handle it. Thus, effective training naturally takes on a cycle of work and rest, stress and recovery, hard day, easy day. Many runners ignore this when it comes to building miles. They may follow a guide such as the 10 percent rule to limit the rate of increase, but they maintain an unrelenting ascent week after week toward their goal mileage. A safer and more effective approach is to increase miles for one to three weeks, then maintain that level for a week or two until your body has adapted to it, before increasing again.

Some runners follow an even more drastic approach, alternating hard and easy weeks. Building toward 140-mile weeks before her Olympic medal in Athens, for example, Deena Kastor reportedly alternated each new mileage high with a recovery week, logging totals of 80, 70, 100, 80, 120, 100, 140, 100, 140, 100… Another top runner, John Mirth, a 55-year old whose running cred’s include qualifying for the Olympic Trials three times and placing 4th master in the 2004 Boston Marathon, adopts a similar pattern, alternating 80-mile weeks with 50-mile weeks. Those of us with a more mortal mileage tally can work with percentages, taking regular “down” weeks of 20 to 30 percent fewer miles before increasing again.

Switchbacking up the mountain takes longer, but it gets you to the top. What’s more, you get to the top strong, healthy and ready to use your new mileage base to kill workouts and races.

READ MORE: Scaling Long Runs to Meet Your Racing Goals