Human power is the rate of work or energy that is produced from the human body. It can also refer to the power (rate of work per time) of a human. Power comes primarily from muscles, but body heat is also used to do work like warming shelters, food, or other humans. World records of power performance by humans are of interest to work planners and work-process engineers. The average level of human power that can be maintained over a certain duration of time is interesting to engineers designing work operations in industry. Human-powered transport includes bicycles, rowing, skiing and many other forms of mobility. Human-powered equipment is occasionally used to generate, and sometimes to store, electrical energy for use where no other source of power is available. These include the Gibson girl survival radio, wind-up or (clockwork) radio and pedal radio.
Available power Normal human metabolism produces heat at a basal metabolic rate of around 80 watts (0.1 Hp). When the human body is producing mechanical power using skeletal muscles, additional waste heat is generated within those muscles. How much waste heat generated depends on how much ATP is being regenerated by aerobic or anaerobic means, as well as the type of muscle fibers involved, with fast-twitch fibers being considerably less efficient than slow twitch fibers. The efficiency can be as high as 56% in the first 30 seconds, then gradually declines to an average of 25% over many minutes. That means the human body generates 3 watts of waste heat for every watt of mechanical output power when that output is sustained for more than a few minutes. This is in addition to the basal metabolic rate which itself can increase to more than 80W due to the additional metabolic load from physical exertion. During a bicycle race, an elite cyclist can produce around 440 watts of mechanical power over an hour and track cyclists in short bursts over 2500 watts; modern racing bicycles have greater than 95% mechanical efficiency. An adult of good fitness is more likely to average between 50 and 150 watts of mechanical power output power for an hour of vigorous exercise while generating roughly 150W to 450W of additional waste heat in the involved muscles. Over an 8-hour work shift, an average, healthy, well-fed and motivated manual laborer may sustain a mechanical power output of around 75 watts. However, the potential yield of human electric power is decreased by the inefficiency of any generator device, since all real generators incur losses during the energy conversion process. It is possible to use exercise equipment for power generation, by attaching the moving parts to components of electric generators; some home gym equipment uses DC generators to power readouts, displays, and control the amount of resistance offered by the machine. The amount of energy generated is so small compared to industrial power sources that the cost of conversion equipment makes it financially impractical. For example, supplying an average United States home solely with electricity generated from exercise equipment for one day would require more than a hundred people to ride stationary bicycles for all of it.
Transport
Several forms of transport utilize human power. They include the bicycle, wheelchair, walking, skateboard, wheelbarrow, rowing, skis, and rickshaw. Some forms may utilize more than one person. The historical galley was propelled by freemen or citizens in ancient times, and by slaves captured by pirates in more recent times. The MacCready Gossamer Condor was the first human-powered aircraft capable of controlled and sustained flight, making its first flight in 1977. In 2007, Jason Lewis of Expedition 360 became the first person to circumnavigate the globe at non-polar latitudes using only human power—walking, biking, and rollerblading across the landmasses; and swimming, kayaking, rowing, and using a 26-foot-long pedal-powered boat to cross the oceans.
General devices and machines
Treadwheels, also called treadmills, are engines or machines powered by humans. These may resemble a water wheel in appearance, and can be worked either by a human treading paddles set into its circumference (treadmill), or by a human standing inside it (treadwheel). Some devices use human power. They may directly use mechanical power from muscles, or a generator may convert energy generated by the body into electrical power. Human-powered equipment primarily consists of electrical appliances which can be powered by electricity generated by human muscle power as an alternative to conventional sources of electricity such as disposable primary batteries and the electrical grid. Such devices contain electric generators or an induction system to recharge their batteries. Separate crank-operated generators are now available to recharge battery-powered portable electronic devices such as mobile phones. Others, such as mechanically powered flashlights, have the generator integrated within the device. Wrist watches can use muscle power to keep their mainsprings wound up. An alternative to rechargeable batteries for electricity storage is supercapacitors, now being used in some devices such as the mechanically powered flashlight shown here. Devices that store the energy mechanically, rather than electrically, include clockwork radios with a mainspring, which is wound up by a crank and turns a generator to power the radio. An early example of regular use of human-powered electrical equipment is in early telephone systems; current to ring the remote bell was provided by a subscriber cranking a handle on the telephone, which turned a small magneto generator. Human-powered devices are useful as emergency equipment, when natural disaster, war, or civil disturbance make regular power supplies unavailable. They have also been seen as economical for use in poor countries, where batteries may be expensive and mains electricity unreliable or unavailable. They are also an environmentally preferable alternative to the use of disposable batteries, which are a wasteful source of energy and may introduce heavy metals into the environment. Communication is a common application for the relatively small amount of electric power that can be generated by a human turning a generator.
Human-powered radio
Survival radio
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