8 ms·

FWIW the specific biological mechanism for fatigue you described is not accurate: https://www.nytimes.com/2006/05/16/health/nutrition/16run.html https://www.nyt

FWIW the specific biological mechanism for fatigue you described is not accurate: https://www.nytimes.com/2006/05/16/health/nutrition/16run.html https://www.nytimes.com/2006/05/16/health/nutrition/16run.ht... but your basic point that you will eventually get tired enough that you can't move any further is true,

ordu 7y ago
I cannot accurate describe biological mechanism because I'm not a chemist and not a biologist. But I do not see how my explanation contradicts your link. Concentration of lactic acid is building up when there are not enough oxygen in the muscles. Lactic acid could be used as a fuel by muscles or a liver, but to do that oxygen is needed. Without it concentration just builds up to the fatal levels. It means, that to get rid of lactic acid, one needs to lower his power output, to move into aerobic zone when body have plenty of available oxygen, more than it needs, and to work there for some time. One could stop completely when tired, then lactic acid through a bloodstream will reach liver, where it will be metabolized into something more useful. I believe in this case the result will be ATP, which will be ejected into a bloodstream and then used by all the variety of cells in the body. So you are going into a debt, when your power output is higher than your aerobic abilities allow. While it is a free debt, interest rate is zero, there is a limit how much lactic acid your body could contain without harm to itself. It is oxygen debt: the more lactic acid you have, the more oxygen you owe to your body. To repay this debt you need to lower your power, to run slower than you could run indefinitely (i.e. without build up of lactic acid). Of course it just one of the mechanism for fatigue. The other one, for example, is the lack of fuel. It is the worst kind -- you could stop and rest for an hour, but it doesn't help. You need to eat and to wait while glucose reaches muscles. Though with the training it comes easier, body learns how to digest food while running, and how to feed muscles, while they are working. If your body have fats, than it can be trained to use them. Mine body doesn't have fats, so if I plan to cycle for a several hours, I need to eat continuously while cycling or after a few hours I'll lose ability to use my legs.

ordu 7y ago

I cannot accurate describe biological mechanism because I'm not a chemist and not a biologist. But I do not see how my explanation contradicts your link. Concentration of lactic acid is building up when there are not enough oxygen in the muscles. Lactic acid could be used as a fuel by muscles or a liver, but to do that oxygen is needed. Without it concentration just builds up to the fatal levels. It means, that to get rid of lactic acid, one needs to lower his power output, to move into aerobic zone when body have plenty of available oxygen, more than it needs, and to work there for some time. One could stop completely when tired, then lactic acid through a bloodstream will reach liver, where it will be metabolized into something more useful. I believe in this case the result will be ATP, which will be ejected into a bloodstream and then used by all the variety of cells in the body. So you are going into a debt, when your power output is higher than your aerobic abilities allow. While it is a free debt, interest rate is zero, there is a limit how much lactic acid your body could contain without harm to itself. It is oxygen debt: the more lactic acid you have, the more oxygen you owe to your body. To repay this debt you need to lower your power, to run slower than you could run indefinitely (i.e. without build up of lactic acid). Of course it just one of the mechanism for fatigue. The other one, for example, is the lack of fuel. It is the worst kind -- you could stop and rest for an hour, but it doesn't help. You need to eat and to wait while glucose reaches muscles. Though with the training it comes easier, body learns how to digest food while running, and how to feed muscles, while they are working. If your body have fats, than it can be trained to use them. Mine body doesn't have fats, so if I plan to cycle for a several hours, I need to eat continuously while cycling or after a few hours I'll lose ability to use my legs.