Running has its share of rules: Replace your shoes every 500 miles. Make 80 percent of your miles easy/20 percent hard. Imbibe electrolyte drinks after the 90-minute mark. Don’t increase your weekly mileage by more than 10 percent per week.

All have long histories of buy-in from runners and most will probably survive as accepted wisdom for years to come. But why? For the purposes of this article, we’re going to take on the 10 percent rule. No one really knows who came up with the guideline but one thing is for sure: many runners and coaches are married to it. Should they be?

The answer depends on who you ask.

Orlando-based runner Shannon Chenoweth, a 39-year old who works in IT, says yes and has adhered to it for the past five years.

“I’ve run five marathons following the rule and haven’t had any injuries,” she says, “so I don’t question it.”

The same with 34-year old physical therapist Justin Feldman of Poughkeepsie, New York, although he puts his own spin on the rule.

“I rate each workout I do on a scale of difficulty from one to 10,” he says. “I multiply that by the time I spend running and then figure out 10 percent of that total.”

Feldman says this makes more sense to him than an arbitrary number. “To me, the faster runs at shorter distance are just as hard on your body as the longer ones, so this allows me to take that into account,” he explains. “If you only considered time and distance, you might still end up overtraining.”

Others say a less rigid approach to mileage buildup is in order. Long-time runner Mark Remy, 47-year old author of The Runner’s Rulebook and creator of, is among them. “I think runners are missing the point here,” he says. “It’s a broader concept, simply that we need to use common sense and build mileage gradually.”

Coach David Roche, a member of the 2014 U.S. mountain running team and 2015 U.S. long distance mountain team, agrees.

“The rule is a way of helping runners avoid too much, too soon,” he says. “It also looks different depending on where you are with your running. An elite, for instance, can take some time off at the end of the season, and then jump right back in at near normal mileage. Not so a beginner.”

Joanna Zeiger, a former Olympic triathlete, U.S. Olympic Trials Marathon qualifier and coach with Race Ready Coaching, says that this fact—that every runner is an individual—must be front and center with the rule. “It should be considered a very loose guideline and a good starting point,” she says. “But it doesn’t stand up to all situations.”

The research, in fact, shows that the 10 percent rule shouldn’t be hard and fast. A 2007 study compared two groups of runners, assigning half the group of about 500 to a 10 percent buildup and the other half to something more aggressive. In the end, both groups had the same injury rate, about one in five. The researchers took the study a step further and gave the 10 percent group a four-week, pre-conditioning program and then pitted them against the more aggressive training group. Again, the results for both groups matched.

Even for those who adhere to the rule might want to consider cut-back weeks in the mix. Roche, for instance, recommends everyone take occasional weeks to pull back from normal mileage.

“They give both the mind and the body a break,” he says. “Often, we don’t even know an injury is in the making. But cutting back on mileage every few weeks, you can shut down the likelihood of developing an injury. You also give your body a chance to absorb the training you have done.”

How to Build Up Safely

If a strict 10 percent rule isn’t the way to go, then, what is? And how might that change from one distance to the next? Roche has some suggestions and breaks them down by specific jumps:

First-Time Half Marathoners

“The key here is to first build up the frequency of your runs,” Roche says, “because the body responds to consistent reinforcement.”

So focus on adding in more runs, even if they are relatively short—in the 3- to 6-mile range. Once you are adjusted to running more frequently, start building up the mileage of those runs. “You want to reach a point where you are activating aerobic metabolism on every run,” Roche explains.

Finally, make sure your long runs are where they need to be. “The hardest part is adapting to longer runs,” he says. “Once you get comfortable with double digits, you will be in good shape for a half.”

Half Marathon to Marathon

This is the place where “things get more complicated,” Roche says, because it is necessary to refuel on longer runs and during a marathon. Most runners will burn through their glycogen (energy) reserves after about 2 hours of running, which means additional calories must be consumed on the run in the form of gels, chews or endurance drinks.

“When training for a marathon, you’re going to be breaking through your glycogen stores,” he says. “So you’re looking at physiological changes.”

The goal with this mileage buildup should be getting up to the maximum mileage you can handle while staying healthy, Roche explains. For decades, the belief was that recreational runners should be able to run 22 to 26 miles in training prior to a marathon, but in recent years a new school of thought has suggested recreational runners are best served if their longest runs falling into the 14- to 20-mile range. If you focus on increasing your weekend long run and the recovery that follows and then perhaps increasing a moderate midweek run to about 10 to 12 miles, you’ll increase your aerobic capacity while also increasing your weekly mileage.

“The focus for the marathon is going to be the progression of your long runs,” he says. “Eventually, you’ll want to manage this buildup so that you can run for 2 to 2-1/2  hours in training and feel good. Once you’re there, it’s a good place to stop adding miles.”

Marathon to Ultra

Intuitively, runners think that training for an ultra-distance race—essentially an event ranging from 27 to 200 miles—means more miles than training for a marathon.

“That’s not always the case,” Roche says. “Some ultrarunners actually run fewer miles than road marathoners.”

When tackling an ultra, Roche likes to see runners spending more time on the trails to adjust to the varying terrain they present, and increasing long-run mileage.

“So it’s like marathon training with longer long runs,” he says. “Every weekend, you run a bit longer than you would for a marathon long run. During the week, however, you can balance it out with shorter runs.”

The longer trail runs are made manageable due to the variation.

“Your body will be changing up its mechanics constantly, so the longer runs won’t present the injury risk they would on the road,” Roche says. “In fact, mixing up your terrain for any distance can be helpful for preventing injury.”

Be Objective

Roche says the 10 percent rule can prove valuable for runners who can’t check themselves objectively, but that in the end, the goal should be to do just that. “You can’t wish yourself healthy,” he says. “Step back, ask if your training is working for you, and if not, readjust. Be willing to leave toughness at the door.”

At the end of the day, some old-fashioned common sense with regards to mileage build up will go a long way. “Everyone wants an equation with running,” says Zeiger, “but in reality, there isn’t one. Running is very individualized.”

Remy agrees.

“Running can and should be simple,” he says. “The 10 percent rule is a nice, easy number to remember, but there’s no need to calculate it and put it on a spreadsheet. Good judgment can go a long way.”