Can you ride a bike? Then you're a marvel

Copied from The Northwest Parkinson’s Foundation Weekly News Update

A runner-up in the Wellcome science writing prize considers the extraordinary human ability to cycle
Catherine Hess

www.guardian.co.uk - Most of us remember our first proper bike. It's a rite of passage, symbolising our transition from "little" to "big" kid. Even more exhilarating is the day we take our first ride without stabilisers. What most of us don't realise is just how complex the art of riding a bicycle actually is. So complex, in fact, that researchers are just beginning to investigate how on earth we manage to propel ourselves, constantly rocking back and forth with the movement of our legs, on two skinny wheels; simultaneously navigating movement in multiple planes while trying to avoid countless obstacles.

Most extraordinary is what the act of riding a bicycle can tell us about the human brain. In 2010 researchers from the Netherlands published a dramatic case study in the New England Journal of Medicine. Medical researchers at Radboud University in Nijmegen examined patients afflicted with Parkinson's disease, a neurological disorder that results in tremors and involuntary muscle movements. In severe cases, Parkinson's affects balance, co-ordination and limb control and can leave patients unable to walk or carry out basic tasks.

One such patient, a 58-year-old man, suffered from what researchers call "gait freezing". He was incapable of walking to the extent that he required visual guides to help him move one foot in front of the other and was unable to turn while walking. After a few steps the patient would lose his balance and would require his wheelchair.

Astonishingly, however, this patient could still ride his bicycle. Flawlessly. Video evidence, submitted with the published case study (and now available on YouTube), shows the patient, with severe tremors in his arms, shuffling slowly and unsurely down a hallway while being guided by another individual. After several steps he begins to stumble forward until he falls to the ground.

In a second video he is seen riding a bicycle with perfect movement and balance, the marked tremors in his arms are gone and he pedals at a consistent pace and with perfect balance and co-ordination. He cycles away from the camera, turns around and cycles back, slowing, stopping and dismounting perfectly. Once dismounted, however, he is again incapable of walking.

This phenomenon is called kinesia paradoxica. While the mechanisms involved are still not understood, the knowledge is invaluable. It may lead to new forms of physical therapy and exercise for people with Parkinson's disease or other neurological disorders that affect movement, co-ordination or balance.

Currently, the "bicycle sign" is being suggested as an effective and inexpensive way to differentiate between Parkinson's and the rarer atypical Parkinson's. One way in which the two diseases differ is in the ability or loss of ability to ride a bicycle. Individuals with Parkinson's who were able to ride a bicycle before the onset of symptoms retain the ability to cycle. Those with atypical Parkinson's do not.

But how is it possible for a man to ride a bicycle when he is essentially wheelchair-bound? More importantly, how does anyone adapt to the sensory whirlwind that is bicycle riding? Research teams at the University of California, Davis in America and the University of Delft, Netherlands, are trying to find out. What they have discovered is surprising.

While we take it for granted that riding a bicycle is as easy as, well, riding a bicycle, it turns out that it is anything but. Led by Professors Mont Hubbard and Ron Hess, American researchers are attempting to model human-bicycle interactions in a similar manner to pilot-aeroplane or motorist-car interactions. However, there are many more physical and neurological processes involved in riding a bicycle than driving a car.

Riding a bicycle involves continuous use of all the human's primary sensory capabilities, visual, vestibular [balance] and proprioceptive [the awareness of one's body and limb positioning]," says Hess. "The latter involves sensors in the arms providing information about steering inputs. What is more interesting though is the ability of the trained cyclist to ride a bicycle 'hands-free'."

Recent research at the University of California, Davis has demonstrated how subtle body leaning by the cyclist enables this behaviour.

"Imagine trying this control technique in an automobile or an airplane," says Hess.

The goal of this research is to understand how the cyclist interacts with both the environment and the bicycle and to develop bicycles that maximise performance, whether the rider is a Tour de France cyclist or a disabled cyclist needing greater stability or control.

What is clear from research into both the human brain and the bicycle is that despite the bicycle's simplicity we have yet to fully understand how it is that we manage to control it, and what is happening in the brain when we do. Our first wobbly bicycle ride, then, is a more remarkable event than we ever imagined