London, Feb 12 (IANS) When it comes to long distance running, humans are some of the best adapted for clocking up miles, even if inefficiently. Scientists have now tried to understand why we have stuck to our inefficient heel first footfall pattern when the rest of our bodies are honed for marathon running.

The paradox puzzled Nadja Schilling and Christoph Anders from Jena University, Germany and Christopher Cunningham and David Carrier from the University of Utah, US, until they began to wonder whether our distinctive heel first gait, inherited from our ape forefathers, might be an advantage when we walk.

The team put young healthy volunteers through their paces to find out why we walk and run heel first.

Measuring the amount of oxygen consumed as their human subjects walked, the team asked the volunteers to walk in one of three different ways: normally, with the heel contacting the ground first; toes first, with the heel slightly raised so that it didn't contact the ground; and up on tip-toes.

Then the scientists asked the athletes to repeat the experiments while running heel first and with their heels slightly raised.

Calculating the amount of energy required to run and walk, the team found that walking with the heel slightly raised costs 53 percent more energy than walking heel first, and walking on tip-toe was even less economical.

However, there was no difference between the runners' efficiencies when they ran with flat feet and up on their toes.

Our 'heel first' gait makes us incredibly efficient walkers, while both postures are equally efficient for runners. Human walkers burn roughly 70 percent less energy than human runners when covering the same distance, said a Utah university release.

However, this efficiency would be completely wiped out if we switched to walking on our toes. 'Our ability to walk economically may largely be the result of our plantigrade [heel first] posture,' says Carrier.

These results were published in the Friday issue of The Journal of Experimental Biology.