New discoveries in cell biology are throwing up some surprises. The average person has roughly equal numbers of what are known as slow and fast fibres in their muscles. Slow fibres operate aerobically and are useful in endurance events like the marathon.
Fast fibres are anaerobic and used in sprinting and weightlifting.
Variations in the amount of different fibres can be used to predict which sports an athlete might be good at. Converting Muscle People with spinal cord injuries have almost no slow twitch muscle fibres in their legs. Fibres are able to convert from slow to fast - but not vice versa. Genetic Engineering Scientists are already talking about the possibility of converting one type of muscle to the other using gene therapy. By inserting genes into muscle cells they may be able to boost the levels of muscle they need most.