UrbanUpdate

First, some disappointing news: No one is capable of crafting a universally-applicable, absolutely-ironclad running routine that prescribes the perfect number of miles or minutes for achieving optimum human performance. But those of you ready to crack the classic actually, zero running is the perfect amount zinger are sorely missing out. Running regularly is definitely healthier than not doing so, in terms of both reducing your risk of heart disease and also increasing the expected duration of your life.

Besides, there are few rules of thumb that should be helpful in the quest to find the perfect routine for your optimum performance. To that end, we asked a few experts to weigh in on how to decide how far and how fast to run—and how to know when it's time to stop.

For the beginners: Stick to basics

According to Road Runners of America certified coach Laura Norris, the first step for novices is to start slow, and to be unafraid of embracing run-walk intervals. Sure, your initial sessions won't double as Rocky training montages, but you need to give bones, muscles, and tendons time to catch up. "Increasing your mileage before your musculoskeletal system adapts increases your risk of injury," she says. Hitting the pavement too enthusiastically is a common mistake, says former NCAA distance coach and New York City-based running coach Sean Fortune, especially among younger, untrained men.

Rather than aiming for specific mileage goals, Norris encourages beginners to reduce the duration of walking intervals until you're up to 30 uninterrupted minutes of running. There's nothing wrong with some cross-training as you work towards that milestone, either; things like swimming, cycling, and the elliptical will help develop aerobic fitness with less impact, Norris says.

On a weekly basis, four or five sessions of these sessions is ideal for maintaining a basic, healthy level of cardio. Ultimately, says running coach Bobby McGee, you want to make sure you're getting to that day's "start line"—whatever that term means for you—healthy and fresh. "If your training did not allow for this scenario, you trained too much," McGee says.

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For the intermediates: Know thyself

Once you've figuratively hit your stride, you're going to figuratively hit a fork in the road, too, and increasing the difficulty sliders can be a tricky task. "There are two indications that you need to change your routine: mental burnout and a physical plateau," Norris says. "The mind and body thrive on variety."

When that moment arrives, it's on you to find a more challenging sweet spot—for example, by pivoting to an outdoors, distance-oriented plan, instead of watching the treadmill clock. Age, injury history, medical conditions, and fitness level should all factor in to this decisionmaking process. This year, for instance, Fortune is aiming for a total of 40 miles per week; that's less than in previous years, but necessary in light of his heavier-than-normal travel itinerary.

For what it's worth, GQ staff writer and recent New York City marathon finisher Clay Skipper estimates that he runs between six and ten miles once every five or six days. It's a routine that would likely garner some tsk-tsking from coaches for its lack of continuity, and Clay knows it: "I don't recommend this training technique," he says. "I landed on that number because it's just long enough and often enough to assuage the dreaded I've probably lost all of the stamina I gained in marathon training feeling that creeps in."

That anxiety isn't unusual, and Fortune cited it as a genuine consideration for runners in search of a sustainable routine. "I have a lot of nervous energy built up each day," he says. "I can fidget, bite my nails, and have trouble focusing if I don't get in some form of exercise. Other people don't have the nervous energy. All of this contributes to each runner's profile in determining their optimal amount of running."

For the experts: It's probably time to relax

After finding that sweet spot, the third stage of runner's guilt is fearing that you've grown complacent, and then pushing too hard, too quickly. Rest assured: You're probably just fine. McGee says this feeling is most often driven by a desire to achieve some arbitrary, preordained time or pace number, without listening to what the body thinks about it. It can also be driven by other factors—for example, the desire to lose a large amount of weight, or to achieve a certain body fat percentage.

Remember, Meb Keflezighi wasn't made in a day, so look out for the telltale signs that you're in too deep: if you're tired, moody, or have trouble sleeping, or find yourself losing your appetite or your sex drive (or both). Overtrained female athletes might miss a menstrual cycle. And not all the red flags involve physical conditions, either. If you're doing a terrible job at maintaining personal relationships, the amount of running you're doing is officially too much running. A good rule of thumb: Ball is life, but running is not.