Maybe your 15-year-old Labrador isn't doing well. Maybe your boss has been pressuring you to stay late. Maybe you were dumped. On your wedding day. With a text. Whatever the reason, when you have a bad day or week, your instinct is to lace up and work it out on the road. But run superstressed, experts say, and your typical interval-induced Zen might elude you. In fact, you could be setting yourself up for injury.

For the most part, running is touted as a mental tonic. Research has shown that your routine four-miler helps keep granule neurons in the brain from firing, making you better able to deal with anger, anxiety, or grief, the negative emotions referred to, collectively, as stress.

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But there's a flip side: Research also indicates that running during an especially rough life patch can make you more susceptible to stress and even injury. Two studies reported that negative psychological states and low levels of life satisfaction and high levels of stress were linked to athletic injuries. "It's paradoxical," says Jim Afremow, a mental performance consultant, runner, and the author of The Champion's Mind. "Running is a favorite stress buster, but it's your stress level that can put you at risk if not managed properly." So what's an anxious/overworked/dumped runner to do?

Races - Places

Back when your caveman ancestors needed to run for their lives from saber-toothed tigers, the body's fight-or-flight response came in handy. Functions unnecessary to a quick getaway, like digestion, would shut down, while functions needed for an escape, like the circulatory system, would kick into high gear, helped by the stress hormone cortisol. A little bit of this chemical still does a runner good. But too much--like the amount you get when bombarded with stress--can "become maladaptive," says Matthew Leroy Silvis, M.D., a sports-medicine physician with Penn State Hershey Medical Group.

Excess cortisol can have harmful effects on bone density and can make you tense up. Run stiff and you're more likely to strain a muscle or tweak a joint, both because you'll be less likely to find your footing should you stumble off of a curb and because tension can throw off your gait, compromising everything from trunk rotation to footstrike.

Serious stress felt over a long period of time can distract a person to the point that he doesn't notice or pay enough attention to what's happening to his body. "It's a type of attentional narrowing; we stop paying attention to other cues in our body," says Gloria Petruzzelli, Psy.D., a clinical sports psychologist and triathlete who counsels runners at California State University, Sacramento. So a runner goes out despite having an achy foot instead of taking a rest day. "Overtraining syndrome can be a common problem among runners who experience stress and negative emotions," Silvis says. And if overtraining leaves you with an overuse injury, a negative state of mind can lengthen how long you stay sidelined, says David Lipetz, director of One Physical Therapy on Long Island. "If an athlete is under a great deal of stress, it can take until the origin of the stressor is resolved to fully recover."

How to Deal

The best strategy for coping with negative emotions is to focus on the present moment, instead of what happened yesterday or what might happen tomorrow, Afremow says. It may sound hokey, but mindfulness, as it's called, was linked in a recent meta-analysis of clinical studies with lower levels of depressive symptoms.

Before you run, try visualizing a scanner moving across your body, passing a comforting sensation through you as it goes from top to bottom, Petruzzelli says. This is your chance to make sure your jaw and shoulders are relaxed.

Then keep your mind focused just on your run. "It's about staying fully engaged with the sensory experience," says Michael Baime, M.D., runner and founding director of the Penn Program for Mindfulness in Philadelphia. Petruzzelli suggests fartlek runs: During this type of "speed play," you are more likely to be thinking about the next tree you are sprinting toward--not the fight you had with your significant other. For the same reason, John Douillard, D.C., author of She Runs to Reclaim Her Identity After Assault, suggests running in an especially scenic place--a view of a beautiful vista will keep your mind from drifting off to stressful thoughts. Running on a trail (where you have to pay attention to the uneven terrain below) or in a crowded park where there is good people- (and dog-) watching can also help keep you present.

Douillard also recommends nasal breathing. "If you breathe through your nose, you're activating predominant calming nerve receptors in the lower lungs," he says. "The goal is longer, slower, deeper breathing versus quick and shallow."

It's also important to pay attention to the stress-busting standbys, including logging enough hours of sleep and maintaining a healthy diet.