Image caption Placing piezoelectric sheets on the street helped power Tokyo's Christmas lights

Harnessing energy from the human body may only generate small amounts of electricity but scientists believe it has a wide range of potentially life-changing applications.

Imagine clothes made with materials capable of generating electricity from either the warmth or movement of the human body.

That is what Professor Steve Beeby has been developing in his laboratory at the University of Southampton.

A vest made of this material could potentially power medical sensors on the wearer's body to carry out periodic checks for high blood pressure or other symptons. The results could be transmitted wirelessly back to a GP or hospital.

Find out more Costing the Earth: People Power is on BBC Radio 4 at 15:30 BST Tue 4 Sept, repeated 21:00 BST, Wed 5 Sept

Listen online afterwards at the above link.

There is potential to reduce regular hospital check-ups with benefits to both patients and a cash-strapped NHS, believes Prof Beeby.

"The idea with energy harvesting normally is you collect energy as you go along and when you have enough, you use it. The electronics go back to sleep and you carry on collecting more energy for the next time."

But making the clothing truly responsive to body movement is the challenge for scientists.

"Clothing is designed to be compliant and not resist your motion and to get electrical energy out you're going to have to do some work," says Professor Beeby.

"It may be best to put this somewhere like your shoe or sock, where there are naturally forces as you walk around."

Power of the heart-beat

Another way of generating electricity is from human blood flow or the movement of internal organs.

For instance the heart's movement has been harnessed to power a pacemaker developed by cardiologist Dr Paul Roberts at University Hospital Southampton.

"Occasionally we'll actually put our hands on the heart and it's astounding how forceful each beat is. You couldn't hold it hard enough to stop it from squeezing - and that's at rest.

"If someone had to get up and run they're able to increase that strength even more, so clearly there's a huge reserve in what the heart is able to deliver," he says.

The pacemaker lead is placed through the heart and a balloon is put in two of the heart's chambers so as each contracts it squeezes the balloon, forcing a magnet down the lead, through a coil to produce an electric charge.

So far Dr Roberts and his team have been able to produce 17% of the power needed for a pacemaker.

Image caption Dr Paul Roberts (left) demonstrates the pacemaker device to the BBC's Tom Heap

Pacemaker batteries have to be replaced every seven years or so via surgery.

Creating an everlasting pacemaker powered entirely by the charge from the owner's own heartbeats, would take out the risk associated with heart surgery as well as saving on costs.

Dr Roberts is well aware of the apparent contradiction of people with heart complaints using heart power to run pacemakers.

"The amount of energy we are potentially taking away from the heart's energy is less than 1% so even in someone with very significant heart failure the percentage is so small we don't think it would any appreciable effect on their overall functions."

Soldier power

At Cranfield University, scientists are working on developing knee brackets to allow soldiers to generate power as they march or run that could eventually replace battery packs.

"I'd like to put the device in a soldier's boot and use that energy. They carry a lot of batteries around with them so there's a massive incentive to reduce the load they carry," says Alice Daniels of Cranfield University.

Scientists are also using piezoelectric devices to potentially generate power from the bounce of a rucksack on a soldier's back as they run.

"The idea behind energy harvesting is you can have an autonomous system so you don't have to pay to change all the batteries," says Daniels.

"Initially the cost of energy harvesting will be higher, but in the long run the payback period will work out."

The great thing is this needs only microwatts of power from your body to save megawatts in the system. Professor Eric Yeatman, Imperial College

Capturing real time information released by humans - such as body temperature - offers the potential to save on the amounts of energy consumed nationwide in institutions like workplaces or schools.

"Buildings use enormous amounts of power for lighting, heating and air conditioning but in a pretty coarse and stupid way that doesn't take much account of people's activity," says Professor Eric Yeatman of Imperial College.

"But if everybody was wearing sensors that were monitoring their activity, and if that was being transmitted into the environment, you could imagine a situation where your home or office could be constantly adapting itself in a predictive way to what you're asking of it.

Professor Yeatman believes such technology could cut down on waste enormously and aid the reduction of global power consumption.

"The great thing is this needs only microwatts of power from your body to save megawatts in the system."

Costing the Earth: People Power is on BBC Radio 4 at 15:30 BST Tue 4 Sept, repeated 21:00 BST, Wed 5 Sept or listen online afterwards at the above link.