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Treadmill v. outdoors - the difference is minimal Add to ...

Alex Hutchinson draws on the latest research to answer your fitness and workout questions in this biweekly column on the science of sport.


Is there any difference between running on a treadmill and running outside?


Running on a treadmill is a bit like making bread with a bread machine: Purists say you are missing the essence of the experience by taking technology's easy way out, while pragmatists say the convenience and results speak for themselves.

Even critics have to admit that running indoors on a treadmill has plenty of benefits, such as controlled temperature, good footing, even pacing and perhaps a big-screen television nearby. But if you're using the treadmill over the winter to train for a 10K road race in the spring, it's important to know whether you are working the same muscles you would if you were pounding the pavement.

"This is actually a very ugly question, to which there's no definitive answer," says Colin Dombroski, a pedorthist at the Fowler Kennedy Sport Medicine Clinic in London, Ont.

More than 30 years of research have produced two schools of thought, Mr. Dombroski says. One holds that treadmill running is fundamentally different because your centre of mass doesn't move while you whip your feet from back to front. The other maintains that, as long as the treadmill is moving at a constant speed, there's no physical difference other than the lack of wind resistance.

The most recent attempt to unravel this mystery comes from researchers at the University of Virginia who used high-speed cameras and special treadmills with force-measuring surfaces to compare joint motion and impacts. The results, published in the journal Medicine & Science in Sports & Exercise last June, showed that there are statistically significant differences in several parameters, such as knee orientation and peak force. But over all, the researchers concluded that the biomechanics of running on a treadmill are close enough to "overground" running that the differences don't matter.

This is the same conclusion that many running coaches have reached through first-hand experience. "There are differences, but they're very minor," says Peter Pimm, a Toronto distance-running coach who has guided Olympians as well as recreational runners for more than 25 years. To compensate for the lack of wind resistance, Mr. Pimm has his runners set their treadmills at a 1-per-cent incline.

One key advantage of treadmills, he says, is that they're generally softer than sidewalks and roads. "People often notice that it's gentler on the knees," he says. "So if you've had joint injuries, it may even allow you to train more."

This advantage, however, may also be the treadmill's greatest weakness: If you stick to the treadmill all winter, the lack of pounding means you don't build the same level of specific muscular endurance needed for the outdoors. So if you jump straight into a road race, Mr. Pimm says, "you may develop muscle soreness and tightness earlier in the race than you otherwise would."

The same caveat applies to running on grass and trails, Mr. Dombroski says. The treadmill won't develop the stabilizer muscles that keep you upright on uneven surfaces.

In both cases, the answer is simple: Mix it up. Try not to rely exclusively on the treadmill - and if weather does keep you indoors for several months, start with a few easy outdoor runs before jumping into a 10K race.

Alex Hutchinson is a former member of Canada's long-distance running team and has a PhD in physics.


Setting the treadmill grade

With no air resistance to slow you down, running on a treadmill is slightly easier than running outside on a calm day. In a 1996 Journal of Sports Sciences study, British researchers found that running on a treadmill set at a 1-per-cent incline consumed about the same energy as running on a flat road. That applies for speeds of about four to five minutes a kilometre. Since wind resistance is proportional to the air speed squared, a smaller incline is sufficient at lower speeds.



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