Should you walk or run for exercise? Here's what the science says.

Is running really a better form of exercise than walking, given that running can lead to more injuries?

At Vox, I sit near health reporter Sarah Kliff, who trains for half-marathons and triathlons with a casualness most people reserve for grocery shopping. But Sarah's also suffered with plantar fasciitis and a stress fracture. At times, she's hobbled around in running shoes for months because everything else hurt too much, and even sported a big blue brace on her left leg to help cushion the tiny cracks in the bones of her foot brought on from too much wear and tear.

In many ways, Sarah is a perfect case study in how to think about the benefits and risks of running versus walking. Running has greater health benefits than walking (Sarah is super fit), but it also carries a much bigger risk of injury (see Sarah's foot brace).

So which effect dominates? To find out, I first searched for "randomized control trials" and "systematic reviews" on running, walking, and exercise at PubMed health (a free search engine for health research) and in Google Scholar. I wanted to see what the highest-quality evidence — trials and reviews are the gold standard — said about the relative risks and benefits of these two forms of exercise.

It was immediately apparent that running can lead to more injuries, and the risk goes up as running programs get more intense. Studies have found that runners have significantly higher injury rates than walkers (one study found that young men who run or jog had a 25 percent higher risk of injuries than walkers), and that ultramarathoners are at an even greater risk. The main running-related injuries include tibia stress syndrome, Achilles tendon injuries, and plantar fasciitis.

Overall, more than half of people who run will experience some sort of injury from doing so, while the percentage of walkers who will get hurt is around 1 percent. Interestingly, it seems you can walk pretty much endlessly without any increased risk of hurting yourself.

That running hurts people shouldn't be surprising. As this study described, "Running produces ground reaction forces that are approximately 2.5 times body weight, while the ground reaction force during walking is in the range of 1.2 times body weight." You're also more likely to trip and fall while running than you are during a walk.

I also learned about some of the incredible health benefits of going fast: Even five to 10 minutes per day of jogging at around 6 miles per hour can reduce the risk of death from cardiovascular disease and other causes. Joggers have been found to live longer than non-joggers even after adjusting for other factors — a difference of 3.8 years for men and 4.7 years for women.

That said, research has found that walking carries significant health benefits, as well. Some studies suggest that you can extend your life and stave off disease by simply walking — and the more, the better.

All this research, while illuminating, didn't offer up any clear conclusions on whether running or walking was better for you overall. So I asked some of the world's leading researchers in this area. Their conclusion? You need to consider the trade-offs.

"Running moderately prolongs life more than walking does," said Peter Schnohr, a clinical cardiologist who has researched many aspects of exercise and health. The key word there is "moderately." Schnohr warned of the emerging research that very strenuous exercise (like triathlon training) can lead to heart problems. Overall, there's a U-shaped association between running and mortality, he said. Too little isn't helpful for health, but too much might be harmful.

"The most favorable [regimen] is two to three running days per week, at a slow or average pace," Schnohr advised. "Running every day, at a fast speed, more than 4 hours per week is not as favorable." And for those who don't like running, he noted, "Fast walking, not slow, also prolongs life. I can't tell how much."

Dutch researcher Luiz Carlos Hespanhol pointed out that in general, running simply delivers health benefits more efficiently than walking does. This study, for example, found that five minutes of running per day is as beneficial as 15 minutes of walking. Hespanhol also said that after one year of training just two hours a week, runners lose weight, reduce their body fat, lower their resting heart rates, and drive down their blood serum triglycerides (fat in the blood). There's even evidence that running can have positive effects on tension, depression, and anger.

Even so, Hespanhol wasn't a total cheerleader for running. A good walking regimen can have similar benefits, he noted. So on running versus walking, it really depends on your values and preferences: "One could choose walking instead of running as a mode of physical activity based on injury risks, since walking is less risky than running," he explained. Or alternatively: "One could choose running because the health benefits are larger and come faster, in a shorter period of time."

To recap: Running improves your health more efficiently than walking does and has greater health benefits per time invested. But even a small amount of running carries more injury risk than walking. And a lot of running (i.e., ultramarathon training) can well be harmful, while the same is never true for walking.

Where does this leave us? All the exercise researchers seemed to agree on one thing: that the best exercise routine is the one you'll actually do. So the answer to the running versus walking question will probably vary from person to person. If you prefer one over the other, stick with that. And if you still can't decide, Hespanhol suggested this: "Why not do both — running and walking — in order to get the best of each?"