The Dominant Leg

Summary of an article by Simone Kosog in the science section of the 'Süddeutsche Zeitung Magazin' 1999.

Robert Schleip

People who are lost in the desert tend to walk in circles with a left spin, i.e. counter-clockwise.

Most or our supermarkets are organized the same way: entrance is on the right, the cashier on the left. Studies have shown that customers tend to feel slightly stressed - increased cardiac pulse, elevated blood pressure, slightly faster walking pace - and buy less when they have to walk in the opposite direction.

Same on the sports field: most track and field sports - from the 400 meter distance runner to the hurdle racer, they all run towards their left. Even the everyday jogger tends to run counter clockwise around the field or lake if he has free choice.

Scientists agree that most of us are not only right handed but also right legged. We kick the ball with the right leg, and if falling forward we catch ourselves more often with the right leg. The right leg is more muscular and makes longer steps in walking, according to Prof. Onur Güntürkün, biopsychologist at the Ruhr university at Bochum/Germany. "It is only a very small difference of a few millimeters, but they are adding up.".

Easy experiment to prove this: walk in closed eyes on the same spot in the room. After a while most of us will tend to turn towards the left.

Yet some of us are left legged. In soccer that carries the advantage that the opponent has more difficulties when trying to dribble the ball around you.

Paradoxically the dominant leg - which tends to be stronger and make longer steps - is most often a bit shorter. Biologist Siegfried Wachtel says that this is not at all surprising since our heavy usage tends to wear it down and shorten it more .

An old guideline in the military infantry makes sense: If a low airplane comes appears from behind on the left side, it will usually not be dangerous, since if it wanted to attach it would have to fly in a rightward curve - which it probably won't do. Yet if it appears from the right side behind, it is better to take cover quickly.

For most people their strength is generally accumulated on the same side; i.e. right handed people are most often also right legged. The most common exception are people which are right legged and left handed, according to the scientists Stern and Schilf who examinded almost 20 million school children.

This left twist effect seems to be generally apparent in animals. Circus horses enter traditionally the arena on the right and circle left wards. Foresters know that a wounded deer will always run away left wards, even if the closest forest is to its right. Even bees tend to circle leftwards when they spiral upwards to gain height in the air.

The basic driver behind this phenomenon seems to be the fact that all cells in nature are composed of amino acids which have a left spin. Chemists can manufacture amino acids with a right spin, yet we can't use them. Apparently both types of amino acids existed in the primordial soup at the beginning of life hundreds of million years ago. Yet life developed only from those with a left spin. The favorite theory is that at that time - when the earth did not yet have the protective ozone shield - radioactive rays from the cosmos did more harm to the amino acids with a right spin. Yet why those with a left spin would be more protected - if at all - is still a mystery.

Additional remark (by Robert Schleip):The science magazine 'Smithonian' had an article a few years ago (which unfortunately I can't find nor do I know the year or issue) about studies of leg dominance in chimpanzees and humans. Interestingly they found that the location of the language centre in the cortex tends to follow the dominant leg, rather than the dominant arm. I.e. if the dominant leg is on the right side (which is organized mostly from the left cortex) then the language centre of the brain will be most likely at the same left side of the cortex which is also occupied with the movements and sensations of that dominant leg. Their explanation was that the dominant leg apparently plays a major role in our antigravity stability and locomotion during the day and thereby might engage the cortex more than the question which hand is used more dominantly.