What is exactly stamina? What happens when it gets trained? Do your lungs get better and more efficient at pumping air?
In: Biology
Heart chambers get bigger, so it can pump more blood per minute. Blood gets more red blood cells, so the same amount of blood can carry more oxygen. Individual cells will get more mitochondria (the cell machines that turn oxygen into fuel), making them able to better use oxygen available. Blood vessels grow to the used parts of the body, getting more blood to relevant areas. Other structural changes happen too, like bones, connective tissue etc all adapt. Muscle cells get a somewhat higher mix of Type I fibers that use oxygen for fuel. And last but not least, technique. You’ll be able to do the movement more efficiently over time, wasting less energy so your ‘fuel economy’ improves.
Cardio adaptations tend to be a bit more short lived, so people can lose a lot of their cardio capacity in just a week or two of not training, but it also improves quickly. Someone who’s youngish and healthyish can go from ‘never runs’ to ‘can run a marathon without stopping’ in six months.
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