Courtesy of The Other 98%, with over 17,000 likes and 4,200 shares. This meme highlights a fitness chain in the Chicago suburbs called “Eco Gym“, which bills itself as an environmentally friendly gym, with the slogan “change your body, change our planet”. While many, like The Other 98%, view this as a “great idea”, it’s really just a marketing gimmick that tricks those who don’t examine the physics and mathematics behind it.
It seems like we’re expending a great deal of energy when we work out, and you might think your spin class could power a city block if it were harnessed. However, the reality is quite underwhelming when human exercise is converted into electricity. Most gym equipment and exercises (including ones at the Eco Gym) don’t create electricity at all. Free weights, pull-up bars, medicine balls, etc. can’t realistically be attached with alternators. The only machines that are harnessing human energy are those like ellipticals and stationary bikes, so we’ll concentrate on those.
Adults of good average fitness can sustain between 50-150 watts of power in a vigorous hour workout on a stationary bike. An elite cyclist might be able to sustain 400 watts, and even the most powerful cyclist can barely sustain 700 watts for a short period before collapsing on the floor in exhaustion (as seen in the video below). This means even the best athlete in the world can barely produce enough electricity to toast a piece of bread.
Assuming your average gym-goer averages 100 watts in their cycling workout, that would generate just .1 killowatt-hour (kWh) of electricity in an hour workout (which is a pretty long session at the gym). The average price of electricity in the US is 12 cents/kWh, so a 1 hour workout would save the gym just 1.2 cents! Even if one biked an hour every day, it would only save the gym 36 cents a month. Therefore, the “savings” that are passed onto the customer don’t actually exist, and is just a marketing gimmick.
Ok, but if we have dozens of people on treadmills in a gym, doesn’t that save significant energy over time? Not really. Here are the average energy use of common appliances. (source)
- Light Bulb- 60 watts
- Desktop Computer- 100 watts
- LCD TV- 213 watts
- Microwave- 1500 watts
- Water Heater- 479 watts
- Central AC- 5,000 watts
Assuming the gym has 20 machines that are used 1/4 of the time (which is generous, as Eco Gym is open 24 hours), its clients might provide 500 watts on average. Enough to power a few lights, a couple TVs, or a small fraction of the air conditioning. In fact, it probably doesn’t create enough electricity to power the hyperbaric oxygen chamber that they offer to their clients.
For more perspective, the average household uses 911 kWh of electricity a month, meaning even if Eco Gym was busy with clients cycling away, they would produce just a fraction of what a single house uses (about 1/3 if we’re generous with their machine usage). Since there are only 34,000 health clubs in the US, even if every gym became an Eco Gym, it would save less electricity than 15,000 households use.
The laws of thermodynamics tell us nothing is free, including calories. The energy we burn must be replaced by food, which takes energy to produce and ship. It takes about 1 food calorie for us to produce 1 watt for an hour. Estimating the amount of energy it takes to produce our food is quite dubious and varies depending on many factors, but one researcher estimates 10 calories of fossil fuel energy are used to produce 1 calorie of food on average. Clearly, exercising causes much more energy and resources to be used, it’s not an equal trade off. Whether one values their health or being “green” more is an ethical question, but the fact remains the more one works out, the more energy they use, and the more they impact the environment. Far from being a “green” activity, pedaling a bike that harnesses your energy into electricity is actually increasing your “footprint”. You are taking far more resources than you give back.
In this sense, if the Eco Gym actually encouraged members to exercise more because of their “energy savings”, they’d be consuming far more, not less resources.
The small savings in electricity that a place like Eco Gym might gain is likely eclipsed by the energy it takes to manufacture the new machines, transport them, retrofit them with the alternators, and install/connect them to an electrical system that can utilize the energy.
Economically, it makes no sense either. Texas State recently retrofitted 30 elliptical machines, for a cost of $20,000 (about $665 per machine). Assuming each machine is used 6 hours a day at 100 watts/hr (a mighty generous assumption), it would produce just 219 kWh in an entire year, a savings of just $26 per elliptical. At this rate, it would take over 25 years for the electricity savings to pay for the cost of the retrofitting! The machines and alternators would likely break down long before that, meaning new units would need to be manufactured, shipped and installed, and the savings never realized.
For personal use, there is a product called Pedal-A-Watt, which attaches to your bike and stores the electricity to a battery that can power household items. It sells for $369, so assuming two people in a household each pedal for 1 hour each day, it would take over 42 years to pay for itself.
If the goal is to minimize energy use and save electricity, this idea is not only poor, but counterproductive. Not only are the savings incredibly small, but they probably are negative when factoring in the production, shipping and installation of these new devices. The reality is that human exercise produces such little electricity that it’s probably not even worth harnessing, unless technology changes considerably. For example, shutting off your air conditioner for a day would probably save more electricity than you create exercising in a year! Perhaps, someday it might make marginal sense if the price comes down (or electricity goes up), but only for aesthetic or consumer preference reasons. It’s never going to have a real impact on “saving the planet”.
If people are still worried about their workout being “green”, the best way to save energy would be to start running/bicycling/lifting from home, as the energy it takes to drive to the gym certainly eclipses any savings earned at an Eco Gym. If one prefers the services and facilities of Eco Gym, or places like it, by all means join up. Just expect to pay more than a budget fitness place, as the equipment is expensive, and the electricity savings don’t come close to making up for it.