I go for a run a few times a week. I like to run at a comfortable pace that allows me to bore my companions with my opinions on various matters. Sometimes I fall in with more serious company who move at a faster pace. This severely restricts my conversation, and my leg muscles feel sore for a while after the run. I've never felt attracted to sprint-running. These events are too explosive, short-lived, and charged with nervous energy for my liking.
Anyone who has taken the remotest interest in running will have noticed the difference in body-build between sprinters and long-distance runners.
Sprinters usually have powerful musculature whereas long-distant runners have a "lean and hungry" look. In this article I will explain some of the basic physiological differences between sprinters and long-distance runners. These, and many other matters, are very nicely explained in the recent book, Diatom to Dinosaurs: the Size and Scale of Living Things by Christopher McGowan (Penguin Books, 1999).
Surprisingly, compared to other animals human beings cannot run very fast. A world-class sprinter can reach 26.6 m.p.h., not much better than an African elephant.
One might think that our relatively poor performance is because we are two-legged. However, other two-legged creatures that are about our size, for example, kangaroos and emus, can run much faster. Also, our 26.6 m.p.h. can only be kept up for a short distance. If we want to run longer distances we have to drop our speed. Top-class marathon runners travel at about 13 m.p.h. Locomotion is effected by our muscles, mainly our leg muscles. The basic unit of organisation in muscle, as in all tissues, is the cell. The muscle cell is called the muscle fibre. Muscle fibres are long cylinder-shaped units that frequently run the length of the muscle.
Muscle fibres have the capacity to actively shorten and passively lengthen again, thereby enabling the muscle to do its job.
The energy required to power the contraction of muscle is derived from the burning of nutrients in our food, principally glucose. Glucose is burned in the cell in two stages.
The first stage, called glycolysis, takes place quickly, does not require oxygen and releases only about 7 per cent of the energy available from glucose. Since it does not require oxygen, glycolysis is called an anaerobic process. The second stage of glucose-burning takes place more slowly, requires oxygen and releases the remaining 93 per cent of the total energy available from the glucose.
The second stage of the burning of the glucose takes place in little organelles in the cell called mitochondria. Since this stage requires oxygen it is called an aerobic or oxidative process.
Muscle fibres come in two basic types. One is called slow-oxidative and the other type is called fast-glycolytic. The slow-oxidative fibres are rich in mitochondria and have a high oxidative capacity. They contract slowly, generate less power than fast-glycolytic fibres, but have high endurance and can continue contracting for long periods. The fast-glycolytic cells contract quickly, generate a lot of power and have a low oxidative capacity and a low endurance. Top sprinters can run 100 metres in about 10 seconds. This explosion of power must be fuelled anaerobically: there simply isn't enough time for the slow aerobic burn. Sprinters need large powerful fast-acting muscles filled with fast-glycolytic fibres. A sprinter does not train for endurance. The primary interest is in achieving maximum acceleration.
This requires large leg muscles, and to build these up sprinters do a lot of weight training. They also practise short-fast runs and explosive starts. These exercises are largely anaerobic.
When muscles do not get enough oxygen to fully burn the glucose they must rely on glycolysis which breaks the glucose down to lactic acid. A prolonged bout of fast running will cause a lot of lactic acid to accumulate in the leg muscles and this is the main cause of stiffness after a run.
Sprinters also need powerful upper bodies. When a sprinter accelerates explosively out of the starting blocks, he pushes on the ground as hard as he can, first with the right leg, then with the left and so on. Because of this the body twists first one way and then the other way. If the sprinter didn't have a sturdy upper body to resist the twisting forces he would swing so much from side to side that it would impair his running. Many female sprinters suffer from this problem because they have less strong upper bodies than their male counterparts.
Marathon runners on the other hand are in for the long haul and need the steady continuous supply of energy that is only available from burning the glucose in the presence of oxygen. They train for endurance, mostly by doing long-distance runs.
This increases the size of the heart and the volume of blood that is pumped to the muscles. It encourages the growth of new vasculature in the muscles to better supply blood. It encourages more mitochondria to appear in all muscle fibres and the muscle fibres to adopt the slow-oxidative chemical metabolism.
What animal holds the world animal speed record? This would be the peregrine falcon which can swoop on its prey at a speed of 217 m.p.h. The fastest land animal is the cheetah which has been clocked at 64 m.p.h. A racehorse has been clocked at 42.9 m.p.h. and a greyhound at 41.7 m.p.h. A world-class sprinter can run at 26.6 m.p.h. A cockroach can only manage 1.8 m.p.h..
William Reville is a senior lecturer in biochemistry and director of microscopy at UCC