Knowledge is the power to reducing your injury risk. Join us on a tour of the bodys components, and look at how they become damaged.
Bones are essentially the scaffolding of the body, and although they have some flexibility in childhood, this largely disappears with age. Structurally, the outer bone, which is thick and dense, covers an inner honeycomb matrix of porous bone, which is suffused with marrow and blood vessels to provide nutrition. Varying in length from a few millimetres to over 50cm, every bone has evolved to maximise lightness, efficiency and strength. Bones are surrounded by a layer of fibrous tissue, the periosteum, which, thanks to a particularly good nerve supply, is very sensitive.
When you break a bone, you also damage the blood vessels nearby, which behave as weve just explained. When bones heal, they form a tissue called callus, which remoulds into normal bone but is often thicker and stronger than the original bone, as though to prevent another fracture should you have a similar accident again.
Runners are plagued by the stress fracture to picture one, think of a crack in a china cup. The fracture occurs as a result of overuse and repeated stress to a bone, and the broken surfaces are only held together by surface tension and the surrounding tissues. Youll probably become aware of a stress fracture by experiencing crescendo pain, which starts when you run, increases to reach a peak, and only eases when you stop.
A doctor will often have to make a diagnosis from your history, as x-rays show little in the early stages, and scans and other investigations are extremely expensive. The risk with a stress fracture is that a minor knock may upset the unsteady equilibrium and cause a complete fracture, which takes twice as long to heal.
The joints between bones are limited in their direction and range of movement by the shape of the adjoining surfaces. These are covered by cartilage, the smooth finish of which is lubricated by synovial fluid, secreted within the joint to give almost frictionless movement. According to the laws of physics and levers, any reduction in a joints range or movability will decrease its efficiency, and from our point of view can only slow the runner.
Muscles come in various forms, but those which link bone are composed of microscopically striated (streaked) tissues, which contain fast- or slow-twitch fibres. If the muscle is joined to bone at each end, muscle contraction will bring the bones together, and an opposing single muscle or group of muscles will reverse the action when it receives the signal to do so.
Muscles are richly supplied with blood vessels, so they bleed freely when injured, but heal rapidly. If you completely rupture a muscle, others will often take over its role and allow you to function reasonably normally, despite the fact that your limbs will look unbalanced. These muscles will strengthen and grow, so you will lose little if any strength.
It is important not to work an injured muscle too vigorously in the early stages, as fresh bleeding can cause the bruise to calcify and lose elasticity.
Body tissues receive oxygen and other nutrients through arteries. These, like the branches of a tree, divide into ever-smaller arterioles and ultimately into capillaries, where the exchange of nutrients and waste can occur. The blood returns through venules and veins in reverse pattern to the heart, which pumps it to the lungs for re-oxygenation and then returns it to the heart again to complete the cycle. Arteries contain muscle within their walls, and the blood in them is under much higher pressure than that within the venous system. This is particularly relevant in understanding the injury and healing cycles.
If you damage the inside or outside of blood vessels by stretching them beyond their elastic limit, youll create faults in their walls, which will bleed. The volume of blood lost will depend on the extent of the damage and the pressure behind and opposing it. If you bleed from an artery, youll almost invariably lose more blood than if you bleed from a vein, and warmer areas in which the vessels are dilated bleed more than cold ones. The greater the amount of bleeding, the more the damage, and hence the longer before healing occurs.
The clotting process begins from the moment that bleeding occurs, as elements within the blood congeal and form fibrous scar tissue. This eventually reorganises itself, and the tissues can become almost as good as new, although much depends on how you approach rehabilitation.
In general, an area that is richly supplied by blood vessels will bleed more freely, but will heal most completely and rapidly.
Ligaments and Tendons
Ligaments are formed of fibrous collagen and serve to loosely join bones. They are generally inelastic and unstretchable. Only if subjected to prolonged strain will they elongate, which results in hypermobility. The classic runners example is the flat foot, which inevitably worsens with both increasing age and mileage!
As muscles tend to be bulky, tendons have often evolved at their extremes to transmit muscle pull in small or awkward spaces, or even around corners. In the latter instance, to prevent friction, they may have a sheath of synovium which provides lubrication. White and shiny but thinner than muscle, tendons are immensely strong but suffer from a relatively poor blood supply, which can delay or prevent healing if they are damaged.
Injuries to ligaments and tendons tend to behave in much the same way as muscle injuries, though theyre slower to heal because of poorer blood supplies. This causes special problems for runners, and healing and rehabilitation must be carefully supervised to optimise recovery times.
The most convenient way to picture the nervous system is as a computer with the brain at its centre. The functional units of the system are neurones, each of which can only conduct impulses in one direction either towards the brain for sensation, or away for motor purposes such as driving the legs. Neurones of both types may both be contained within a single nerve. Many bodily functions, such as heart rate and digestion, are involuntarily controlled by what are called the sympathetic and para-sympathetic nervous systems. The classic example of their function is the urge to evacuate the bowels prior to a race!
A nerve containing both motor and sensory fibres may be completely severed in a deep body wound, and all the body parts supplied by that nerve away from the spine will be without pain but paralysed. More commonly, though, nerves can become trapped or bruised, which causes pain, numbness or weakness. Although full recovery will occur if the pressure on the nerve is relieved, at one millimetre per day, it may take several weeks!