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The Foot - Part One "To print see bottom left"

 By Jonathan Blood-Smyth

Ever since our distant ancestors started standing up on two feet and we gradually adopted the upright bipedal gait we now find so easy, efficient and useful we have had some problems with our feet. They have had to adapt to taking all the locomotion forces which used to be shared by four limbs. Walking on two limbs has enabled a vital shift in our abilities, the adaptation of the other two limbs to carry the hands, hands which can manipulate objects independently of walking and standing. This has allowed us, for better or worse, to control the world.

To appreciate what the foot has to withstand it is illuminating to think a little about the physics of the forces involved in what the feet have to manage to do their job. Feet complain amazingly little and are an elegant solution to the competing demands they must satisfy. Our feet undergo 150 percent of our body weight every time we take a step, even in relaxed, non-stressful walking. If we then consider vigorous pursuits and sports such as aerobics, tennis, football or jogging, the levels of force increase to 3 or 4 times the levels in walking.

The key to how it is possible to put a greater load through our body than our weight is to consider the addition of speed to the equation. The amount of force involved is a product of speed and weight, with the forces increasing significantly as the speed of the movement increases. It is easy to understand this when thinking about the dreaded weighing scales, not a popular thought mostly. Stepping onto that scale you will see, for a second or so, the scale jumps right up beyond your weight then settles back to where you hope it might. To simulate the stresses of vigorous movements such as jumping, jump right onto that scale and see the scarily high level the dial gets to!

After considering the speed of movement we have to go back and talk about weight, not a favourite subject but one that involves much anxiety and stress and applies a considerable pressure. Our extra pounds are not just passengers hanging about, they make up an important part of the speed times weight equation. On vigorous movements that extra pound is multiplied many times, to stress our joints, ligaments, bones and muscles. This makes it harder to exercise the heavier we get, setting up a vicious circle where increasing weight leads to decreasing activity. At this point our bodyweight becomes a factor limiting our ability to exercise to reduce our bodyweight.

Humans need to do a lot of things on and with their feet and the complex mechanics of the foot ensures that it can take the forces necessary, adapt to them and produce the desired forces to achieve what we want. The divisions of the foot are the midfoot, the hindfoot and the forefoot. In the forefoot the five bones of the metatarsals are long and prominent and often feature in high profile soccer stars' injuries. The toes are made up of small bones called the phalanges, with two in the great toes but three in all the remaining toes.

The foot is a complex mechanism for taking, adapting and producing forces to allow us a wide variety of mobility choices to enable us to pursue whatever activity we choose. The main segments of the foot are the forefoot, the midfoot and the hindfoot. The forefoot includes the metatarsals and the phalanges. The five metatarsals, often featuring in the news when a sports star fractures one, are long and prominent bones in the front of the foot, with the phalanges making up the small bones of the toes.

Jonathan Blood Smyth, editor of the Physiotherapy Site, writes articles about Physiotherapists, physiotherapy, physiotherapists in Birmingham, back pain, orthopaedic conditions, neck pain and injury management. Jonathan is a superintendant physiotherapist at an NHS hospital in the South-West of the UK.

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