If we can’t see air, can fish see water ?

The adaptive system plays a role here. Fish can’t see water because their optical speed of the velocity of what they see is limited. We as humans can’t see air because the air consists of particles that are to difficult for us to see with our evolved retinas to distinguish.

the answer is lactic acid from anaerobic respiration. the acid in lactic acid is what creates sore and burning muscles. if you think about how acid burns that will give you a clue for questions like this.