kick into gear

[Egyption Arrow]

In the of the Merciful Allah,
Hi guys, could you please give me the meaning of " kick into gear" in the following statement"As breathing stops and the sleeper's blood oxygen level plummets, the body's emergency system kicks into gear, causing.
...............". Thanks alot ahead.

 

[Horsa]

You could understand it as 'starts working'

 

[Egyption Arrow]

I need more than this common explanation, which is based on estimating the meaning from the context. More exactly, I'd like to be aware of its original difinition, precisely, and etymolgy. I've searched several dictionaries for it and all I've got so far is that idiom means, informally, to make (a car) increase in speed, esp. in auto racing: He kicked his car into high gear.

 

[apex2000]

Kick into gear is simply an expression that has crept into normal usage from engineering, but particularly biking. The action of changing gear on a motorbike which is done, or at least always was done, by using the foot.
It does not come from any medical source. To us it provides an immediate picture of an engine coming to life or moving from idling to fast motion.