Can the human body be used as a renewable source of energy? Scientists and researchers are looking for ways to harness human power as a viable means of clean energy.

Human power or using motion to power appliances is spreading worldwide. Harvesting human power is a free and renewable energy source that has been used since man started to walk. Powering appliances through human motion is also an added incentive to couch potatoes to get up from their couches and start exercising. Companies are also investing more in the technology in a drive to go greener and save more resources.

Many suggestions have been made for producing energy from physical activity but the location that human power could be best exploited is in gyms around the world. A company from Woodinville, Washington is tapping into gym-goers unused energy with their Green System a novel way to convert human power into usable energy.

SportsArt Fitness' Green System consists of recumbent and upright bikes as well as elliptical trainers that captures 75 percent of the watts people generate when they use the devices. Each machine is hooked to a box that stores the energy; the boxes in turn are hooked together and routed to an inverter that can handle up to 2,000 watts. According to SportsArt Fitness, 2,000 watts are enough to power a microwave for 2.5 hours or a 27-inch flatscreen television for 17 hours. The entire system can pay for itself in three years. Interested companies can buy the exercise machines for about $3,500 to $7,000 while the inverter costs about $3,000.

Meanwhile, South Korean electrical engineers are looking into ways of using the human voice to power mobile phones. Dr. Sang-Woo Kim from the Sungkyunkwan University in Seoul is developing a way for sound power to generate electricity. The technology uses a sound absorbing pad connected to two electrodes that sandwich tiny strands of zinc oxide. When sound waves hit the absorbing pad, the tiny zinc oxide wires compress and release to generate an electric current that can charge the mobile phone's battery. A prototype of the technology was able to generate 50 millivolts of electricity. While it's not enough to charge a phone properly, Dr. Kim and his colleagues are working on altering the materials to absorb more energy.

As oil prices rise, a sustained drive for alternative energy sources will push the need for more human-powered technology. Many more human-powered devices will feature in consumers' lives in the near future.