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By Dr Ben Garrod, Teaching Fellow, Anglia Ruskin University and Nick Owen, Senior Lecturer Biomechanics, School of Sport and Exercise Science, Swansea University.

If you want to know “everything” about someone then you might look at the clothes they wear, the books they read or the people they spend time with – but these things might change day-to-day or even between breakfast and lunch. To really know someone, you have to get right down to their bones.

Our skeletons are a natural framework, on which hang our muscles, nerves, tendons and skin. Walk into any museum and have a look at the skeletons. It’s easy to tell which skeletons belonged to slithering snakes or gliding gulls, but have a closer look and suddenly you’ll see that the slender shoulder blades, big flat paws and an extra finger-like digit allow the humble mole to shovel through the earth, or the long arms and missing thumbs permit the spider monkeys’ arboreal acrobatics.

We are the same: every human skeleton differs massively. It’s not only possible to distinguish old from young skeletons and those from males and females, but in certain situations, we can even tell what those people did when they were alive.

Skeletons, and the bones that make them up, are often thought of as immutable, particularly after maturity has been reached. However, nothing could be further from the truth. Just as evolutionary adaptation can produce the mole or the spider monkey, shorter term adaptation of the skeleton happens to us all. People are often surprised to hear that bones are not only important organs in the body but that they also respond to exercise in a similar way to muscles.

Elite athletes are good examples of this. Training from an early age, throughout puberty and into adulthood, the constant and repetitive force patterns produced, say in cross-country running, will stimulate the bones of the legs. The bones respond by adapting (remodelling and modelling) their shape and size, as well as mineral content, better to resist the forces involved in cross-country running. But the leg bones of a cross-country runner would have a different shape to those of a football player, for example. This is all down to forces. The forces on a cross-country runner are pretty much in a forward and backward direction (a straight line); by contrast, a football player has to run in all directions and therefore resist forces in all directions, resulting in more circular tibias (lower leg bones). Tennis players, on the other hand, are an example of when the adaptations are "sided". That is, as tennis players generally use only one arm when hitting a ball, the racket arm, it is that arm which adapts. Studies have found that in elite tennis players there is a significant difference between their lower arm bones. The bowmen aboard the ill-fated Tudor warship Mary Rose were an extreme example of this type of process. They were required to perform a very limited (but highly skilful) pattern of movement (drawing the bow and loosing the arrow) that involved enormous forces (up to 81kg/180 lbs). If anything is going to change bone, that is.

This happens to us all, to a greater or lesser extent. In days gone by manual labourers would start from an early age and their job would be repetitive – let’s say digging. This would load certain bones and stimulate them to adapt, thus allowing a resilience to the forces involved. You could say we are what we do...