Before the dawn of inventions, most of the work people did was powered by sheer human strength. "Historically, if you go way back, everything was human-powered," said Mark Archibald, chair of the Human-Powered Vehicle Committee of the American Society of Mechanical Engineers. But then the motor came along and did much of the heavy lifting for us.
Today many people are turning back to human-power as an energy source. It's free, it's clean and it's good for the heart.
The following is a look at some of the ways energy can be harvested from people -- for both transport and for electrical devices.
ABOVE: Scottish cyclist Graeme Obree designed this face-down, headfirst bike, which lets him pump his legs horizontally instead of up and down. The design improves the aerodynamics by reducing drag. In September 2013, Obree tested the bike in Battle Mountain, Nev., and reached 56.62 mph, breaking the record for prone cycling’s previous speed of 54.9 mph.
Currently, the fastest machine powered by a human is the VeloX3, designed by the Human Power Team Delft from The Netherlands. Their recumbent bicycle encased in a shell called a monocoque break the world speed record last September by going 133.78 km/h (83.127 mph).
In 2010 a team of students from the University of Toronto made a successful slight of the first human-powered airplane. Unlike previous human-powered airplanes, the Ornithopter, as it was named, flapped its wings like a bird. It flew for 19.3 seconds, covered a 158 yards and reached an average speed of 15.8 miles per hour. The same team is working on its own version of a human-powered helicopter.
At the University of Maryland a team successfully flew the Gamera II, setting a record for a human-powered helicopter flight. Although they did not achieve the duration and height necessary to win the Sikorsky Prize, which is given to a team that can reach 10 feet and hover for 60 seconds, they were able to fly a few inches off the ground for 50 seconds -- more than anyone before them.
The first designs for a human-powered sub date to the 16th century, and there was one -- the Confederate submarine H.L. Hunley -- that made an appearance during the Civil War.
More recently teams of engineering students have been building one-man versions designed for drivers in SCUBA gear, powered by rear propellers. At least one design, by Swedish industrial designer Milko Ozlu, uses oars.
Steven Polowy, president of the Human-Powered Submarine Team at the University of Michigan, noted that such subs have technical constraints all their own. "The big one is air," he said, because a person exerting him or herself uses a lot. Another issue, he said, is efficiency -- his team used a stair-stepper motion to power the propellers instead of bicycle-like pedaling.
Humans move around a lot. We walk, jump and dance. So why not use all that kinetic energy? Via piezoelectric devices, that's now possible. Piezoelectricity comes from substances that generate current when they are compressed, bent or stretched. The most common application is lighting stoves (the lighter uses a piezoelectric material to generate a spark).
Now some inventors have proposed using these materials in objects that humans come into contact with and move. For example, dance floors, roads or sidewalks. Walking or even driving on the surfaces would put pressure on embedded piezoelectric materials, which could then send an electrical current out to be used to power lights.
Other ideas include embedding these materials into backpacks that would generate power for soldiers, who might be walking far from base camp. Tiny devices embedded into special knee braces could also create energy from walking.
In 2008 the East Japan Railway Company experimented with a power-generating floor, which produced enough to power ticket kiosks.
Bicycles are the most obvious human-powered transport today, but HumanCar Inc., wants to build a car that can go short distances powered by human muscle. It isn't much like the pedal-cars some might remember from when they were kids; this one moves via a rowing-like motion and the wheels are powered with a gearing system not unlike that of an old-fashioned sewing machine (in which a wheel is made to go faster via a flywheel).
The car also includes an electric motor for longer trips. An added bonus: under human power, the car can charge small electronic devices. The top speed is only about 30 miles per hour, so it isn't made for highways. If you want to buy one, it will cost, though: about $85,000. HumanCar CEO Chuck Greenwood notes that there are only a half-dozen units built and that's why they cost so much; in the future he hopes to get them mas-produced.
Sometimes called a cycle rickshaw, these have been a staple form of transport in countries such as India, China and Bangladesh (where they are brightly decorated). While their use is decreasing in Southeast Asia, it is rising in cities like New York, where there are 1,112 licensed drivers and 850 pedicab license plates (the number is capped by law). Other cities where they have become popular with tourists include Hamburg, London, and San Francisco.
Several designs for powering implanted devices with blood sugar have been floated in the last few years, most based on the fuel cell. One recent idea uses it to power brain implants, while another was proposed for pacemakers. This might be something like what the writers of The Matrix had in mind, though you'd need to still feed the humans and you wouldn't get much current. It is, however, enough for the average medical device.