Posted by: Charlie | 2004/01/08


Why does one person run faster than the other even though they both have the same height, weight, build and fitness levels? Please explain in terms of force production ability.

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Our expert says:
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I see that you have asked two questions which are fairly similar, and I’ll try to answer them both at once, because the answers overlap quite a bit, so this and the question below are answered in one go.

I must say that neither answer is a simple one. In fact, you could do a PhD thesis on these questions, and people have. Some of it is to do with the force generating capability of the muscles, but this is not the only reason, and so I would not limit the answer to this alone.

Now, the first important thing is that things like height, weight and build are only external features which have some, but not a huge deal of relevance to running performance. So, the answers lie not in the external, but in what is happening internally during exercise. So, there are many different ways of looking at this. You have touched on one, the force generating capacity of the muscle, and others would be circulation, metabolism, biomechanics and the central nervous system, which controls the lot.

With the muscles, you get two types of muscle fiber – slow twitch and fast twitch. The slow twitch fibres are more adapted to endurance exercise, whereas the fast twitch fibres are able to produce more force, at a more rapid rate, but fatigue more rapidly. So, you might be able to outrun someone over 1 or 2 km, but as soon as the distance increases to over 10 km, it works the other way around, because if you have a high proportion of fast twitch fibres, then you are more adapted to short, high intensity exercise. Of course, this is an oversimplification, but the basic summary is that if you have a high proportion of slow twitch fibres, you’ll never be a sprinter, whereas a high proportion of fast twitch fibres means that long distance is probably not your strong point. That’s why you often hear that people ore born into sprinting or long distance running.

Another really important factor is metabolism – when you exercise you use carbohydrates and fats as the mian source of fuel, and some people are better adapted to use fat than others. The reasons for this are complex, but the effect of this is that these people are able to exercise for much longer periods – the athletes in the Ironman for example are fat burners, and this allows them to exercise for upwards of 8 hours, whereas others, without this genetic ability and training (because you can improve your ability to use fuel efficiently) don’t have this capability. Also the rate at which you can use carbohydrates (which are the more important source during short to medium length exercise, like your running and spinning) is determined by certain key enzymes, and these levels can be increased by training. So, two people can be trained differently (an important point here is that training and fitness are not the same thing, and so equal fitness does not mean equal ability, because training does not equal fitness, if you follow my logic) and therefore will perform differently because they are more efficient in the use of fuel stores. So, I would hazard a guess that one reason why some people are able to sustain high intensity cycling is that they are trained differently, and have the ability to use carbohydrate stores at quite a raped rate and therefore sustain the supply of energy to the muscle. Others are less able to do this, but are perhaps able to go for longer at a lower intensity – slow and steady vs. short and fast. This is something that is largely genetic, but is open to midifcation by training – if you do a fair amount of training at these high intensities, like intervals training, then you improve the ability to exercise at higher intensity and for longer periods.

I hope you are following this so far. Now, another important factor is biomechanics – this refers to how the limbs and joints move. It’s maybe more relevant in running than in cycling. The bottom line is that certain people just move more efficiently than others, and so they would be able to run a certain speed using less effort, because what they are doing is more efficient. This too is something that imporves with training as well.

Then, finally, and maybe the most important thing, is that all these systems and factors are controlled by the brain. When you exercise, all these factors, the fuel use, the muscle, the circulation etc. are all being monitored by the brain – it’s called homeostasis, and it means to maintain the system in balance. So, if anything starts or threatens to go slightly out of balance, like for example, the level of oxygen getting to the active muscles, then the brain slows you down. If you are running out fuel, then the brain senses this and slows you down. If you are using fuel very rapidly, then one of the by-products is a decrease in pH of the blood, and it may be that the brain slows you down so that this is controlled as well. It is a hugely complicated, advanced system, and we don’t know much about how this regulation works. We certainly don’t know enough to be able to say why some people are better than others at high intensity exercise, but in the end, it comes down to how the brain regulates pacing and performance One of the effects of training, apart from modifying the signals that go to the brain like improving your metabolic system and efficiency, may be that these signals are interpreted differently, so that you are able to exercise whereas before, you would slow down.

Now you probably have been told more than you ever wanted to know – if this is particularly interesting to you, then I would suggest treating yourself to Lore of Running, 4th edition, because it’s the most comprehensive discussion of these issues around, and it’s very readable as well.


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