It is a synonym for a purely competitive market (perfect competition). On this type of market the supply (of a homogenous good) is big, and the price is determined by the demand of this goods. Therefore, suppliers on this market are known as price takes. So the model shows supply, demand and therefore the price and quantity in equilibrium.
No one knows for sure exactly what does cause muscle soreness. But a lot of scientists now think that pain is caused by microscopic tears in the muscles when a certain exercise or activity is new or difficult. These VERY SMALL tears eventually later on produce inflammation, and corresponding pain, 24 - 36 hours later? So I think it's true- and I am sure they rebuild. Because your body repairs it. That's what I think :)