Q I dont seem to be able to run more than 5K without becoming incredibly uncomfortable. This is a real shame, as Id love to tackle a marathon. Can people simply be better suited to short distances?
A The old adage about horses for courses also applies to humans. Some of us have the wrong genes for endurance events, and no amount of training or dedication can change that. For example, no one would expect Dwain Chambers to be comfortable running 5K, no matter how many miles he put in.
The trainability of our aerobic capacity is limited to at most 30 per cent; in some individuals it may be as little as five per cent. So, as one of my professors used to say, if you want to be an elite athlete, choose your parents carefully.
Our aerobic capacity is determined by a combination of factors, including the relative proportions of muscle-fibre types in our muscles (whether we have a greater proportion of aerobic, slow-twitch, fatigue-resistant fibres; or anaerobic, fast-twitch fibres). If we have a greater proportion that are slow, we are better equipped for endurance events.
Conversely, if we have a greater proportion of fast-twitch fibres we are likely to be better suited to short, intense events. Top sprinters typically have 80 per cent fast-twitch fibres, while marathon runners are up to 80 per cent slow-twitch. But the majority of the population has an even mix of both types.
The fact that you feel you struggle more once you get above 5K may indicate that youre genetically suited to short-duration, high-intensity exercise. This doesnt mean that you cant run, it just means that you should choose training that suits your physiology, such as interval sessions.
Im a big fan of interval training (short bouts of high-intensity work interspersed with recovery); its good for lots of things: weight management, strength development and general fitness. It burns calories, it develops strength because your muscles contract at higher forces than in slower running, and it will also develop your central cardiovascular fitness.
Dr Alison McConnell, exercise physiologist