Me
a cool down
increases the heart rate
relax the body
tightens up the leg muscles
increases your stress level

ANSWER:

A cool down helps to relax the body.

EXPLANATION:

The cool down phase of exercising is an essential part of a work-out as it helps to slow down the activity level gradually. Cool down is the phase in which the heart rate and breathing can be returned to normal levels. Cool down also helps to remove metabolites from the body. It helps the muscles to relax and also prepare for the "next exercise session".