What are the real differences in running outdoors vs. on a treadmill?

Treadmills can spark contentious debate among runners. Are they a legitimate training tool or a second-rate simulation? If you’re concerned you’re not getting the most from your treadmill workout or are worried about a rough transition from tread to outdoor running, fret not, said Jenny Hadfield, co-author of “Running for Mortals” and columnist for the Runner’s World blog Ask Coach Jenny.

“You can still get a great workout on the treadmill,” she says. “I hate that judgment associated with treadmill running, that it doesn’t offer as good of a workout. It’s still running.”

Not that there aren’t clear differences.

“Depending on the method you choose, some muscles work when others don’t,” A. Lynn Millar said. Millar is professor of physical therapy at Winston-Salem State University with a Ph.D. in exercise physiology and a fellowship at the American College of Sports Medicine. “There are a few muscles working differently when you propel yourself in outdoor running versus the treadmill propelling you. In outdoor or track running, you have to push yourself forward. There isn’t that activity on the treadmill, but there may be other muscles getting work.”

This, Millar explained, is what those in the field deem “specificity of exercise,” when specific muscles are targeted in training. Since you’re working different muscles depending on the type of running, expect to have a transition period when alternating between them.

Some professional running coaches like Janet Hamilton of Atlanta-based Running Strong consider treadmills a semi-simulation of running. “I don’t give it a one-for-one equality. Outside, you have to push your body through air — even if there’s no wind. The faster you go, the harder the resistance. You’re running in place on a treadmill. You’re not really having to push your body over the ground.”

So does that mean you’ll burn more calories one way or the other? Not necessarily, Millar said, noting that “there are minor differences, but they’re not worth quibbling about. You can achieve moderate-to-vigorous intensity whether you’re indoors or outdoors.” According to Millar, oxygen consumption is about the same.

Still, many believe that they need to push themselves harder on a treadmill to compensate for a perceived inequity in the workout.

“I see it all the time: People think they need to abuse themselves by setting their treadmill incline at a constant hill,” Hadfield said, adding that this sense of punishment only hurts your workout.

The incline rule is one she hears people cite all the time. “People want to make treadmill running really hard, so they crank it to something like a 12 percent incline. But you aren’t going to encounter many of those types of hills outdoors.”

She recommends keeping the incline between 2 to 5 percent and alternating it to avoid injury: “Beyond that starts to alter your stride and can really strain your muscles. There’s not a purpose for it unless you’re training for mountain running.”

Hamilton, who also teaches certification courses for the Road Runners Club of America, insists such a constant incline doesn’t accurately reflect the outdoor terrain or the way runners behave outdoors. “You wouldn’t go out your front door and find the steepest hill and say, ‘I’ll go that way.”‘ Instead, she recommends simulating a rolling course — going uphill for a while and then bringing it back down.

Alternating the speed is another alternative, Millar said. “It can also beat the boredom some find with treadmill running.”

And if you’re a beginner, Hadfield recommends not even worrying about the incline. She suggests keeping a zero incline and just “learning to run with good form.” Just like in strength training, good form is essential to exercise efficiently and prevent injury. “Some people push themselves for the cardio performance, but I say to keep your form,” she says. “When you start to lose your form, you start to lose the efficiency of muscle groups and you’re not able to get through the workout as well.”

One sure sign of bad form on the tread: if you find yourself bending forward to keep up with the pace. In this case, Hadfield recommends lowering the speed and focusing on keeping your back straight.

If you’re looking to transition outdoors, make sure to give yourself some time to adjust.

“Know that the pace from your treadmill workout won’t translate,” Hadfield said. “Running outside is not necessarily harder. It’s just different, and your body has to acclimate to that.” Aside from the biomechanical differences of outdoor running, there are environmental factors like weather, wind resistance and uneven ground to consider. Hadfield suggests individuals start by heading outdoors once a week and increasing that time gradually. Within a few weeks, she says, most individuals can successfully transition.

While the battle rages on between the two running methods, one thing is clear: either one will keep you healthy.

“For general health and fitness, it doesn’t matter which one you’re doing — as long as you’re doing something,” Millar said. McClatchy-Tribune Information Services.