the accumulation of acid lactic (propanoloic acid)
it can overwork the muscles and so its important to let the body return to normal once the "event" has passed.
The muscles will atrophy (shrink) if not used.
you excersise
They contract
you will die
you exhale (:
contrast
What happens when a muscle shortens is that it is contracting. This is when the fibers of the muscles generate tension.
muscles relaxes
Im not expert, but isn't it the diaphragm and rib muscles, the muscles between the ribs, internal and external intercostals.
A disadvantage of interval training is that some people tend to overwork themselves. It is important to give your muscles time to recover from any training, there is a difference between building muscle and tearing muscle.
No, that might kill you