What's the greenest way to exercise in the winter?

Illuminating answers to environmental questions.
Nov. 30 2010 7:07 AM

Is There a Greener Way To Work Out?

How to burn more calories with fewer watts.

Treadmills. Click image to expand.
If you must work out inside, an elliptical trainer is a better choice than a treadmill

I normally prefer to get my exercise outside. But when I got home from work yesterday, it was pitch dark and freezing, so I went to the gym. Staring at the rows of treadmills, elliptical trainers, and stationary bikes, I couldn't help but wonder: Which is the best choice for the environment?

Your instinct to get outside is commendable, since many gyms are temples to environmental degradation (not to mention breeding grounds for all sorts of little nasties). The cavernous buildings, air-conditioned to bone-chilling temperatures for the handful of senior citizens working out at 10 a.m. on weekdays. The televisions in front of every machine. The jacuzzi that no one ever uses. It's enough to turn even the most athletic environmentalist into a locally grown, organic couch potato.

If you don't want to vegetate through the dark months, there are a few things you can do to minimize the impact of your gym visits. First, stay off the treadmill. Treadmills are, by far, the most popular machines in the club, but they're also the most prodigious consumers of energy.

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On average, a treadmill uses between 600 and 700 watts of energy. That's the equivalent of watching three or four 46-inch LCD televisions or leaving 50 compact fluorescent light bulbs burning, for the duration of your workout. If you ran for two-and-a-half hours per week—the government's recommendation for ordinary adults—generating electricity for the treadmill would emit about 110 pounds of carbon dioxide annually. * (That's about 1 percent of the annual CO2 emissions of the average car.)

Treadmills' power consumption varies significantly by model, though. A recent test of five leading brands showed a range of 280 watts to 928 watts, although the lower end represents a belt speed of 3.5 miles-per-hour—more of a stroll than a workout. Heavier runners also increase power consumption. 

As a treadmill ages, it can consume 30 percent more energy than it did in its younger days. Your gym can prolong a machine's peak efficiency by vacuuming around it frequently and occasionally cleaning out the dust, dirt, and shoe rubber that builds up between the belt and deck.

If you forswear the treadmill and saunter over to your gym's stationary bikes and elliptical trainers, you'll be doing the earth—and your knees—a favor. Those machines typically provide resistance to your force using a magnetic brake. The harder you work, the harder the machine has to work against you. But even at maximum resistance, they require six to seven times less energy than treadmills.

Many commercial-grade elliptical trainers and stationary bikes—the types you might find in a modern gym—are completely self-powered these days. The energy the rider or strider generates feeds back into the machine to power the brake and the electronic display—those flashing green LEDs use about five to 10 watts of energy. Setting aside manufacturing inputs, that means a ride on the stationary bike generates no carbon. Strong bikers could even power a 15-inch LCD television during their workouts. But manufacturers don't usually offer that feature, since some people can't produce that kind of wattage.

(Stair machines are a mixed bag. The traditional pedal-style machines are often self-powered, but the stepmills, which look like a moving staircase, consume about the same amount of energy as a plug-in elliptical trainer.)

Gyms are willing to pay a premium for the self-powered machines because they can put them anywhere without worrying about outlets or wires. But, from a purely financial perspective, they don't make a lot of sense for the home user. Commercial-grade elliptical trainers can cost twice as much as their flimsier residential counterparts, a difference nearly impossible to make up for in energy savings. At prevailing electricity rates, you'd have to use your commercial-grade elliptical trainer nonstop for nearly 20 years to recover the extra $2,000 or so you paid for the self-powered option.

A few gyms are jumping on the human-powered bandwagon with particular vigor. A Connecticut-based company called Green Revolution retrofits spinner bikes to convert pedal power into electricity. A hard-working class can keep a gym lit while it's riding and power some of the televisions. But the package is relatively expensive and not yet widely available, so you might have a hard time finding a people-powered gym.

In the meantime, encourage your gym to green things up a bit. A few large televisions generally run less electricity than individual TVs on every machine. A sign on the screen reminding users to turn it off after use could save a kilowatt-hour per unit, per day. Ask the staff to nudge the thermostat up a little in the summer, and down a little in the winter. (Climate control accounts for far more energy than all the treadmills combined.) If you're looking for a new gym, ask what they're doing for the environment. You might be impressed. Some Lifetime Fitness clubs, for example, use recycled pool water to flush their toilets.

Of course, you could stop being such a baby, pull on some synthetic long johns, and train outside through the winter. Zero watts required.

Correction, Nov. 30, 2010: The original stated that a treadmill produces 110 tons of carbon dioxide annually. In fact, it's 110 pounds. Return to the corrected sentence.

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Brian Palmer writes about science, medicine, and the environment for Slate and the Natural Resources Defense Council. Email him at explainerbrian@gmail.com. Follow him on Twitter.

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