That spot - where the powerful tendon from the large calf muscle, the gastrocnemius, and its smaller partner the soleus, join the heel bone - is, indeed, a vulnerable place for any human. So vulnerable is it, it's often called the Achilles tendon. If that tendon is torn or severed, the calf muscles no longer control the foot, and the victim won't be able to walk properly.

And although this usually happens when the person is running or playing sport, sometimes the victim does no more than take a step forward or put most of his weight on one foot. Usually this happens because there's been some long-term damage to the tendon, either from over-use, a lot of road running or misuse. Many of us favour one leg or one foot, so one Achilles tendon takes more strain than the other.

The Achilles tendon is particularly vulnerable to long-term damage because it gets all its oxygen and nutrients from the blood vessels in the heel bone (the calcaneus), and this isn't the best supplier at the best of times. If the heel has been knocked around by a lot of road running or erratic but intense periods of exercise, it becomes inferior.

Most people who suffer an Achilles tendon rupture are in their late youth or middle age (say, 30 to 50). This makes sense because it takes a good 10 to 20 years of misuse before the tendon finally gives up the strain.

Most of us don't make our livings fighting hard physical battles, as Achilles did, but there's another kind of warrior among us: the weekend warrior. These are desk-bound workaholics who take to the soccer field, basketball or tennis court with vengeance at weekends. They're vulnerable to Achilles tendon ruptures.

How do you know if you're in danger?

People who have had ankle tendon problems, have been given steroid injections in the ankle or have used the drug fluoroquinolone are at risk.

And what should you do if it happens? Get some ice on it, and get to a doctor or hospital emergency department.