A person runs up several flights of stairs and is exhausted when they get to the top. Later, they walk up the same stairs and do not feel as tired. Why is this? Does it take more work or energy to run than to walk? Why?
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The amount of work put out is identical but when running we are putting out the work at a greater rate.
There are a great many losses that occur when doing this.
So the work that we must do is greater. i.e the efficiency falls.
Here are some of the losses. The legs must accelerate forward and backwards with each stride.
This takes kinetic energy. The amount of this energy increases with the square of the speed. And this energy does not contribute to the climbing of the stairs.
The muscles themselves are less efficient at higher rates. A greater fraction of the energy produced is lost in the form of heat in the muscles. So again we need to use more energy even though we are not putting it into the stairs.
Our biochemical processes, such as respiration, become less efficient at higher power outputs.
Finally as already mentioned it takes time to remove waste products and to resupply glycogens.
If we have performed the same work in less time, and if we have exceeded our bodies ability to perform these actions then the tiredness is simply the body instructing us to rest to give time for the processes to be complete.
Note that as you get fitter, you can increase the rate of doing work before this condition sets in.
If you trained regularly you could run up the same stairs without feeling tired because the body is now capable of completing all the processes in the available time.
There are a great many losses that occur when doing this.
So the work that we must do is greater. i.e the efficiency falls.
Here are some of the losses. The legs must accelerate forward and backwards with each stride.
This takes kinetic energy. The amount of this energy increases with the square of the speed. And this energy does not contribute to the climbing of the stairs.
The muscles themselves are less efficient at higher rates. A greater fraction of the energy produced is lost in the form of heat in the muscles. So again we need to use more energy even though we are not putting it into the stairs.
Our biochemical processes, such as respiration, become less efficient at higher power outputs.
Finally as already mentioned it takes time to remove waste products and to resupply glycogens.
If we have performed the same work in less time, and if we have exceeded our bodies ability to perform these actions then the tiredness is simply the body instructing us to rest to give time for the processes to be complete.
Note that as you get fitter, you can increase the rate of doing work before this condition sets in.
If you trained regularly you could run up the same stairs without feeling tired because the body is now capable of completing all the processes in the available time.
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Both the cases work is same. When running we spent energy quickly and energy generation system in our leg muscle does not get necessary time to release waste into blood so quickly. so we feel pain in leg miscle.
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They got stronger so they don't feel as tired. It takes more work to run because it takes more acceleration to run