I used to earn a living from my legs. I worked for a circus, where I rode astride elephants. This mainly involved using my quads, hams and calf muscles, with which I had to clasp the elephant's neck to prevent me falling off. Other circus artistes' legs worked all sorts of far more impressive tricks, from the contortionist winding them around her neck as she did the crab to the hula-hoop girl's splits. Legs aren't designed to do any of these astonishing manoeuvres, which is why their performance is such an attraction. We can, however, train our limbs to do all sorts of things they aren't supposed to.

But walking - legs' primary purpose - is automatic. The remarkably complicated set of movements that begins with a heel touching the ground and ends with the toes leaving it is done without thought. It's so easy that a young adult will typically walk at 100 metres a minute effortlessly. If we did stop to consider exactly how we did it, we'd probably be permanently rooted to the spot.

Although walking is automated, it's still controlled by the brain through the spinal cord. The pattern of muscle activity is generated by a network of neurons called the central pattern generator. But in many animals, such as cats, dogs and rabbits, running or hopping can take place independently of control from the higher centres of the brain.

This, of course, is impressive. Many attempts have been made to replicate such rhythmic movements in humans, with the hope of enabling those whose spinal cord has been damaged, and who therefore don't have a direct line of communication between lower limb and brain, to walk again. But even the most sophisticated experiments to make computers stimulate muscle patterns haven't yet enabled anyone to stride out successfully.

The importance of walking is made clear in our language, which sees moral and physical uprightness as synonymous. To stand on your own two feet, to find your legs, to stand up for yourself, or to have your feet planted firmly on the ground - all attribute independence and control. Conversely, to say someone is on their last legs, doesn't have a leg to stand on, or is legless, is to attribute mental frailty or failure. Without us realising it, our language rewards walking. What does this mean for those of us who, like my wheelchair-using daughter, can't throw one leg in front of the other? How does someone who literally can't stand on their own two feet be seen as metaphorically doing so? Perhaps this presumption of mental feebleness is why some disabled people, such as former Superman Christopher Reeve, become over-concerned with walking as a primary goal; although his paralysis has brought him a whole host of difficulties, his stated aim is to "be on my feet again". How otherwise, our language assumes, could he be an upright, erect, upstanding citizen?

We feel obliged to rigorously examine our vocabulary for any unacceptable sexist or racist connotations, but curiously we feel no such need to reassess any words or phrases that portray walking as a moral as well as physical condition. It seems that when it comes to being biased towards the able-bodied, language is exempt from criticism. Ironically, the slogan of the Christopher Reeve Paralysis Foundation is "Stand up for those who can't!"

But although we may have purged our language of sexist assumptions, legs are still enslaved to sexual stereotyping. As an elephant girl, I had my shapely, strong legs swathed in feminine fishnets. In the circus, male artistes shave their legs and wear tights, too. But no other men would dare do so in public. Unlike arms, which are far more flexible, legs must conform: a man's should be muscular and smothered in hairs; a woman's should be slender and shaved. Unlike the male's, the length of the female femur, tibia and fibula are crucial. Barbie's pins are legendary. Female shanks also carry class connotations. If a businesswoman wears a suit with a skirt, she is expected to cover her legs with tights. Not to do so would suggest she is working class, and undermine her. Unattractive, naked legs generally imply a lower social status, as the knobbly-knee contest testifies.

My legs have now retired from the ring, and haven't seen a pair of serious fishnets for years. As a result of their new line of employment - mindlessly walking me to work - you'd barely recognise them from their circus days; they're neither a better nor worse shape, just different. But as long as they're walking, they give me standing. We all ought to sit down and think about that.