# What is Limiting Factor in Running Fast? [closed]

Say a person can do a 400m run in 1:00, but is unable to do a 1600m in 4:00. What is most likely the main limiting factor in this? What is holding back being able to keep going at this pace for longer? The respiratory system? The lungs? I am assuming that the legs, etc. are strong enough to perform this. I am more interested in what the relative importance of things like the heart and lungs are in this task.

Maybe another way to look at it is for a person who is fairly physically fit through years of exercise, how important are the heart and lungs and other systems in anaerobic exercise?

To me, it seems like the lungs and the ability to get oxygen to the muscles are more important than the heart being able to increase to a high beats per minute, but I am not sure.

• Someone who can do 400m in 60 seconds should expect to be able to do 1600m in 4:30. Are you able to do 4:30? Oct 16 '16 at 12:26
• The person I am referring to has a 400m time of 65 seconds, but a mile time of 5:50. Oct 19 '16 at 19:37

There are several factors that restricts humans to run at very high speed over longer distance. Muscle fatigue, body's ability to consume oxygen and making use of the stored energy are a few. In simple terms, when you move at fast speed, you'd need more fuel. Your body has a limit under which it works. When you do intense workout, you'd need constant supply of energy and your muscles fibers need to handle the breakdown appropriately. That's why sprinting and marathon are 2 different things. In the first you give it all you have over a short distance, on the other, you conserve by restricting the speed to make it over a larger distance.

If you use a calculator like McMillan.com then you'll see what you should be able to do - equivalent efforts - for different distances like going from 400m in 60 seconds to 1600m in 4:40.

I think the reason for the difference that you or the person your talking about is that the 400m run is being done more as a sprint than the 1600m run which cannot be done as a sprint. Perhaps the problem is exaggerated by trying to sprint a lap or two in the 1600m run which can typically be sustained only about 45-60 seconds.

Some proof of this can be found in the McMillan calculator where the sprint time for a 400m sprint is a good bit faster than the 400m speed pace.

Ive also been experiencing something like this at 800m and I suspect its because Im sprinting much of the 400m but not sprinting much in the 800m. Im starting to think its about running close to VO2 max pace instead of all out since VO2 max pace corresponds to a 8 minute race and going all out is only 1-2 min of race pace.